Measurements of charged-particle production in pp, p$-$Pb, and Pb$-$Pb collisions in the toward, away, and transverse regions with the ALICE detector are discussed. These regions are defined event-by-event relative to the azimuthal direction of the charged trigger particle, which is the reconstructed particle with the largest transverse momentum ($p_{\mathrm{T}}^{\rm trig}$) in the range $8<p_{\mathrm{T}}^{\rm trig}<15$ GeV$/c$. The toward and away regions contain the primary and recoil jets, respectively; both regions are accompanied by the underlying event (UE). In contrast, the transverse region perpendicular to the direction of the trigger particle is dominated by the so-called UE dynamics, and includes also contributions from initial- and final-state radiation. The relative transverse activity classifier, $R_{\mathrm{T}}=N_{\mathrm{ch}}^{\mathrm{T}}/\langle N_{\mathrm{ch}}^{\mathrm{T}}\rangle$, is used to group events according to their UE activity, where $N_{\mathrm{ch}}^{\mathrm{T}}$ is the charged-particle multiplicity per event in the transverse region and $\langle N_{\mathrm{ch}}^{\mathrm{T}}\rangle$ is the mean value over the whole analysed sample. The energy dependence of the $R_{\mathrm{T}}$ distributions in pp collisions at $\sqrt{s}=2.76$, 5.02, 7, and 13 TeV is reported, exploring the Koba-Nielsen-Olesen (KNO) scaling properties of the multiplicity distributions. The first measurements of charged-particle $p_{\rm T}$ spectra as a function of $R_{\mathrm{T}}$ in the three azimuthal regions in pp, p$-$Pb, and Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV are also reported. Data are compared with predictions obtained from the event generators PYTHIA 8 and EPOS LHC. This set of measurements is expected to contribute to the understanding of the origin of collective-like effects in small collision systems (pp and p$-$Pb).
$R_\mathrm{T}$ distribution using events with trigger particles $5<p_\mathrm{T}^\mathrm{trig}<40~\mathrm{GeV}/c$ in the pseudorapidity range of $|\eta|<0.8$ and with $p_\mathrm{T}>0.5~\mathrm{GeV}/c$ in pp collisions at $\sqrt{s}=2.76~\mathrm{TeV}$
$R_\mathrm{T}$ distribution using events with trigger particles $5<p_\mathrm{T}^\mathrm{trig}<40~\mathrm{GeV}/c$ in the pseudorapidity range of $|\eta|<0.8$ and with $p_\mathrm{T}>0.5~\mathrm{GeV}/c$ in pp collisions at $\sqrt{s}=5.02~\mathrm{TeV}$
$R_\mathrm{T}$ distribution using events with trigger particles $5<p_\mathrm{T}^\mathrm{trig}<40~\mathrm{GeV}/c$ in the pseudorapidity range of $|\eta|<0.8$ and with $p_\mathrm{T}>0.5~\mathrm{GeV}/c$ in pp collisions at $\sqrt{s}=7~\mathrm{TeV}$
Collective behavior has been observed in high-energy heavy-ion collisions for several decades. Collectivity is driven by the high particle multiplicities that are produced in these collisions. At the Large Hadron Collider (LHC), features of collectivity have also been seen in high-multiplicity proton-proton collisions that can attain particle multiplicities comparable to peripheral Pb-Pb collisions. One of the possible signatures of collective behavior is the decrease of femtoscopic radii extracted from pion and kaon pairs emitted from high-multiplicity collisions with increasing pair transverse momentum. This decrease can be described in terms of an approximate transverse mass scaling. In the present work, femtoscopic analyses are carried out by the ALICE collaboration on charged pion and kaon pairs produced in pp collisions at $\sqrt{s}=13$ TeV from the LHC to study possible collectivity in pp collisions. The event-shape analysis method based on transverse sphericity is used to select for spherical versus jet-like events, and the effects of this selection on the femtoscopic radii for both charged pion and kaon pairs are studied. This is the first time this selection method has been applied to charged kaon pairs. An approximate transverse-mass scaling of the radii is found in all multiplicity ranges studied when the difference in the Lorentz boost for pions and kaons is taken into account. This observation does not support the hypothesis of collective expansion of hot and dense matter that should only occur in high-multiplicity events. A possible alternate explanation of the present results is based on a scenario of common emission conditions for pions and kaons in pp collisions for the multiplicity ranges studied.
CF vs qinv
CF vs qinv
CF vs qinv
The first measurements of $\mathrm{K^{*}(892)^{0}}$ resonance production as a function of charged-particle multiplicity in Xe$-$Xe collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.44 TeV and pp collisions at $\sqrt{s}=$ 5.02 TeV using the ALICE detector are presented. The resonance is reconstructed at midrapidity ($|y|< 0.5$) using the hadronic decay channel $\mathrm{K^{*0}} \rightarrow \mathrm{K^{\pm} \pi^{\mp}}$. Measurements of transverse-momentum integrated yield, mean transverse-momentum, nuclear modification factor of $\mathrm{K^{*0}}$, and yield ratios of resonance to stable hadron ($\mathrm{K^{*0}}$/K) are compared across different collision systems (pp, p$-$Pb, Xe$-$Xe, and Pb$-$Pb) at similar collision energies to investigate how the production of $\mathrm{K^{*0}}$ resonances depends on the size of the system formed in these collisions. The hadronic rescattering effect is found to be independent of the size of colliding systems and mainly driven by the produced charged-particle multiplicity, which is a proxy of the volume of produced matter at the chemical freeze-out. In addition, the production yields of $\mathrm{K^{*0}}$ in Xe$-$Xe collisions are utilized to constrain the dependence of the kinetic freeze-out temperature on the system size using HRG-PCE model.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in pp collisions at \sqrt{s}$ = 5.02 TeV for 0-1\% multiplicity class.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in pp collisions at \sqrt{s}$ = 5.02 TeV for 1-5\% multiplicity class.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in pp collisions at \sqrt{s}$ = 5.02 TeV for 5-10\% multiplicity class.
The Chiral Magnetic Wave (CMW) phenomenon is essential to provide insights into the strong interaction in QCD, the properties of the quark-gluon plasma, and the topological characteristics of the early universe, offering a deeper understanding of fundamental physics in high-energy collisions. Measurements of the charge-dependent anisotropic flow coefficients are studied in Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic ($v_{2}$) and triangular ($v_{3}$) flow coefficients of positively and negatively charged particles as a function of their event-wise normalized number difference, is reported for inclusive and identified particles. The slope $r_{3}^{\rm Norm}$ is found to be larger than zero and to have a magnitude similar to $r_{2}^{\rm Norm}$, thus pointing to a large background contribution for these measurements. Furthermore, $r_{2}^{\rm Norm}$ can be described by a blast wave model calculation that incorporates local charge conservation. In addition, using the event shape engineering technique yields a fraction of CMW ($f_{\rm CMW}$) contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for $f_{\rm CMW}$, and in the 10-60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level.
Normalized $\Delta\it{v}_{2}$ slope of charged hadrons as a function of centrality in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV.
Normalized $\Delta\it{v}_{2}$ slope of kaons as a function of centrality in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV.
Normalized $\Delta\it{v}_{2}$ slope of pions as a function of centrality in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV.
The production of K$^*$(892)$^\pm$ meson resonance is measured at midrapidity ($|y|<0.5$) in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using the ALICE detector at the LHC. The resonance is reconstructed via its hadronic decay channel K$^*$(892)$^\pm \rightarrow \rm{K^0_S \pi^\pm}$. The transverse momentum distributions are obtained for various centrality intervals in the $p_{\rm T}$ range of 0.4-16 GeV/$c$. The reported measurements of integrated yields, mean transverse momenta, and particle yield ratios are consistent with previous ALICE measurements for K$^*$(892)$^0$. The $p_{\rm T}$-integrated yield ratio 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) in central Pb-Pb collisions shows a significant suppression (9.3$\sigma$) relative to pp collisions. Thermal model calculations overpredict the particle yield ratio. Although both simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas MUSIC+SMASH tends to overpredict them. These observations, along with the kinetic freeze-out temperatures extracted from the yields of light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which increases towards central collisions. The $p_{\rm T}$-differential yield ratios 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) and 2K$^*$(892)$^\pm$/($\rm{\pi^+ + \pi^-}$) are suppressed by up to a factor of five at $p_{\rm T}<2$ GeV/$c$ in central Pb-Pb collisions compared to pp collisions at $\sqrt{s} =$ 5.02 TeV. Both particle ratios and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor shows a smooth evolution with centrality and is below unity at $p_{\rm T}>8$ GeV/$c$, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 0-10\% centrality.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 10-20\% centrality.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 20-40\% centrality.
The transverse momentum ($p_{\rm T}$) and centrality dependence of the nuclear modification factor $R_{\rm AA}$ of prompt and non-prompt J$/\psi$, the latter originating from the weak decays of beauty hadrons, have been measured by the ALICE collaboration in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. The measurements are carried out through the ${\rm e}^{+}{\rm e}^{-}$ decay channel at midrapidity ($|y| < 0.9$) in the transverse momentum region $1.5 < p_{\rm T} < 10$ GeV/$c$. Both prompt and non-prompt J$/\psi$ measurements indicate a significant suppression for $p_{\rm T} >$ 5 GeV/$c$, which becomes stronger with increasing collision centrality. The results are consistent with similar LHC measurements in the overlapping $p_{\rm T}$ intervals, and cover the kinematic region down to $p_{\rm T}$ = 1.5 GeV/$c$ at midrapidity, not accessible by other LHC experiments. The suppression of prompt J$/\psi$ in central and semicentral collisions exhibits a decreasing trend towards lower transverse momentum, described within uncertainties by models implementing J$/\psi$ production from recombination of c and $\overline{\rm c}$ quarks produced independently in different partonic scatterings. At high transverse momentum, transport models including quarkonium dissociation are able to describe the suppression for prompt J$/\psi$. For non-prompt J$/\psi$, the suppression predicted by models including both collisional and radiative processes for the computation of the beauty-quark energy loss inside the quark$-$gluon plasma is consistent with measurements within uncertainties.
Non-prompt J/$\psi$ fraction as a function of transverse momentum in Pb-Pb at 5.02 TeV, centrality 0-10%
Non-prompt J/$\psi$ fraction as a function of transverse momentum in Pb-Pb at 5.02 TeV, centrality 10-30%
Non-prompt J/$\psi$ fraction as a function of transverse momentum in Pb-Pb at 5.02 TeV, centrality 30-50%
The first measurements of skewness and kurtosis of mean transverse momentum ($\langle p_\mathrm{T}\rangle$) fluctuations are reported in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$$=$ 5.44 TeV and pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector. The measurements are carried out as a function of system size $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle_{|\eta|<0.5}^{1/3}$, using charged particles with transverse momentum ($p_\mathrm{T}$) and pseudorapidity ($\eta$), in the range $0.2 < p_\mathrm{T} < 3.0$ GeV/$c$ and $|\eta| < 0.8$, respectively. In Pb$-$Pb and Xe$-$Xe collisions, positive skewness is observed in the fluctuations of $\langle p_\mathrm{T}\rangle$ for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum bias pp collisions are also reported here. Kurtosis of $\langle p_\mathrm{T}\rangle$ fluctuations is found to be in good agreement with the kurtosis of Gaussian distribution, for most central Pb$-$Pb collisions. Hydrodynamic model calculations with MUSIC using Monte Carlo Glauber initial conditions are able to explain the measurements of both skewness and kurtosis qualitatively from semicentral to central collisions in Pb--Pb system. Color reconnection mechanism in PYTHIA8 model seems to play a pivotal role in capturing the qualitative behavior of the same measurements in pp collisions.
Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in pp collisions at $\sqrt{s}$ = 5.02 TeV.
Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV.
Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV.
The production cross sections of ${\rm D^0}$ and $\Lambda^+_{\rm c}$ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity ($|y|<0.5$) by the ALICE Collaboration in proton-proton collisions at a center-of-mass energy $\sqrt{s}=13$ TeV. They are described within uncertainties by perturbative QCD calculations employing the fragmentation fractions of beauty quarks to baryons measured at forward rapidity by the LHCb Collaboration. The ${\rm b\overline{b}}$ production cross section per unit of rapidity at midrapidity, estimated from these measurements, is ${\rm d}\sigma_{\rm b\overline{b}}/{\rm d}y|_{|y|<0.5} = 83.1 \pm 3.5 (\mathrm{stat.}) \pm 5.4(\mathrm{syst.}) ^{+12.3}_{-3.2} (\mathrm{extrap.})\,\mu$b. The baryon-to-meson ratios are computed to investigate the hadronization mechanism of beauty quarks. The non-prompt $\Lambda^+_{\rm c}/{\rm D^0}$ production ratio has a similar trend to the one measured for the promptly produced charmed particles and to the p$/\pi^+$ and $\Lambda/{\rm K^0_S}$ ratios, suggesting a similar baryon-formation mechanism among light, strange, charm, and beauty hadrons. The $p_{\rm T}$-integrated non-prompt $\Lambda_{\rm c}/{\rm D^0}$ ratio is found to be significantly higher than the one measured in e$^+$e$^-$ collisions.
$p_{\mathrm{T}}$-differential D$^{0}$ production cross section in pp collisions at $\sqrt{s}$ = 13 TeV
$p_{\mathrm{T}}$-differential $\Lambda_\mathrm{c}^{+}$ production cross section in pp collisions at $\sqrt{s}$ = 13 TeV
$p_{\mathrm{T}}$-differential non-prompt $\Lambda_\mathrm{c}^{+}$/non-prompt D$^{0}$ ratio in pp collisions at $\sqrt{s}$ = 13 TeV
Measurements of the production cross sections of prompt ${\rm D^0}$, ${\rm D^+}$, ${\rm D^{\ast +}}$, ${\rm D_s^+}$, ${\rm \Lambda_{c}^{+}}$, and ${\rm \Xi_{c}^{+}}$ charm hadrons at midrapidity in proton$-$proton collisions at $\sqrt{s}=13$ TeV with the ALICE detector are presented. The D-meson cross sections as a function of transverse momentum ($p_{\rm T}$) are provided with improved precision and granularity. The ratios of $p_{\rm T}$-differential meson production cross sections based on this publication and on measurements at different rapidity and collision energy provide a constraint on gluon parton distribution functions at low values of Bjorken-$x$ ($10^{-5}-10^{-4}$). The measurements of ${\rm \Lambda_{c}^{+}}$ (${\rm \Xi_{c}^{+}}$) baryon production extend the measured $p_{\rm T}$ intervals down to $p_{\rm T}=0(3)$~GeV$/c$. These measurements are used to determine the charm-quark fragmentation fractions and the ${\rm c\overline{c}}$ production cross section at midrapidity ($|y|<0.5$) based on the sum of the cross sections of the weakly-decaying ground-state charm hadrons ${\rm D^0}$, ${\rm D^+}$, ${\rm D_s^+}$, ${\rm \Lambda_{c}^{+}}$, ${\rm \Xi_{c}^{0}}$ and, for the first time, ${\rm \Xi_{c}^{+}}$, and of the strongly-decaying J/$psi$ mesons. The first measurements of ${\rm \Xi_{c}^{+}}$ and ${\rm \Sigma_{c}^{0,++}}$ fragmentation fractions at midrapidity are also reported. A significantly larger fraction of charm quarks hadronising to baryons is found compared to e$^+$e$^-$ and ep collisions. The ${\rm c\overline{c}}$ production cross section at midrapidity is found to be at the upper bound of state-of-the-art perturbative QCD calculations.
$p_{\mathrm{T}}$-differential $\mathrm{D}^{0}$ production cross section at midrapidity ($|y|<0.5$) in pp collisions at $\sqrt{s}$ = 13 TeV Branching ratio of $\mathrm{D}^{0}\rightarrow\mathrm{K}^-\pi^+$: $(3.95 \pm 0.03)\%$. Global relative uncertainty on BR: $0.8\%$ Global relative uncertainty on luminosity: $1.6\%$
$p_{\mathrm{T}}$-differential $\mathrm{D}^{+}$ production cross section at midrapidity ($|y|<0.5$) in pp collisions at $\sqrt{s}$ = 13 TeV Branching ratio of $\mathrm{D}^{+}\rightarrow\mathrm{K}^-\pi^+\pi^+$: $(9.38 \pm 0.16)\%$. Global relative uncertainty on BR: $1.7\%$ Global relative uncertainty on luminosity: $1.6\%$
$p_{\mathrm{T}}$-differential $\mathrm{D}^{+}$ production cross section at midrapidity ($|y|<0.5$) in pp collisions at $\sqrt{s}$ = 13 TeV Branching ratio of $\mathrm{D}^{*+}\rightarrow\mathrm{D}^0(\rightarrow\mathrm{K}^-\pi^+)\pi^+$: $(2.67 \pm 0.03)\%$. Global relative uncertainty on BR: $1.1\%$ Global relative uncertainty on luminosity: $1.6\%$
Charged-particle jet yields have been measured in semicentral Pb$-$Pb collisions at center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}} = 5$ TeV with the ALICE detector at the LHC. These yields are reported as a function of the jet transverse momentum, and further classified by their angle with respect to the event plane and the event shape, characterized by ellipticity, in an effort to study the path-length dependence of jet quenching. Jets were reconstructed at midrapidity from charged-particle tracks using the anti-$k_{\rm T}$ algorithm with resolution parameters $R =$ 0.2 and 0.4, with event-plane angle and event-shape values determined using information from forward scintillating detectors. The results presented in this letter show that, in semicentral Pb$-$Pb collisions, there is no significant difference between jet yields in predominantly isotropic and elliptical events. However, out-of-plane jets are observed to be more suppressed than in-plane jets. Further, this relative suppression is greater for low transverse momentum ($<$ 50 GeV/$c$) $R =$ 0.2 jets produced in elliptical events, with out-of-plane to in-plane jet-yield ratios varying up to 5.2$\sigma$ between different event-shape classes. These results agree with previous studies indicating that jets experience azimuthally anisotropic suppression when traversing the QGP medium, and can provide additional constraints on the path-length dependence of jet energy loss.
Charged-particle jet yields, R=0.2
Charged-particle jet yields, R=0.4
q2-large/q2-small, R=0.2
The elliptic flow ($v_2$) of $\rm D^0$ mesons from beauty-hadron decays (non-prompt $\rm D^0$) was measured in midcentral (30-50%) Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector at the LHC. The $\rm D^0$ mesons were reconstructed at midrapidity ($|y|<0.8$) from their hadronic decay $\mathrm{D^0 \to K^-\pi^+}$, in the transverse momentum interval $2 < p_{\rm T} < 12$ GeV/$c$. The result indicates a positive $v_2$ for non-prompt $\rm D^0$ mesons with a significance of 2.7$\sigma$. The non-prompt $\rm D^0$-meson $v_2$ is lower than that of prompt non-strange D mesons with 3.2$\sigma$ significance in $2 < p_{\rm T} < 8$ GeV/$c$, and compatible with the $v_2$ of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties.
$p_\mathrm{T}$-differential elliptic flow coefficient $v_2$ of non-prompt $\mathrm{D^0}$ mesons in the 30-50% centrality class in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02~\mathrm{TeV}$.
The pseudorapidity dependence of elliptic ($v_2$), triangular ($v_3$), and quadrangular ($v_4$) flow coefficients of charged particles measured in Pb-Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}=5.02$ TeV and in Xe-Xe collisions at $\sqrt{s_{\rm NN}}=5.44$ TeV with ALICE at the LHC are presented. The measurements are performed in the pseudorapidity range $-3.5 < \eta < 5$ for various centrality intervals using two- and multi-particle cumulants with the subevent method. The flow probability density function (p.d.f.) is studied with the ratio of flow coefficient $v_2$ calculated with four- and two-particle cumulant, and suggests that the variance of flow p.d.f. is independent of pseudorapidity. The decorrelation of the flow vector in the longitudinal direction is probed using two-particle correlations. The results measured with respect to different reference regions in pseudorapidity exhibit differences, argued to be a result of saturating decorrelation effect above a certain pseudorapidity separation, in contrast to previous publications which assign this observation to non-flow effects. The results are compared to $3+1$ dimensional hydrodynamic and the AMPT transport model calculations. Neither of the models is able to simultaneously describe the pseudorapidity dependence of measurements of anisotropic flow and its fluctuations. The results presented in this work highlight shortcomings in our current understanding of initial conditions and subsequent system expansion in the longitudinal direction. Therefore, they provide input for its improvement.
$v_{2}\{2\}$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Pb}-\mathrm{Pb}$ at $\sqrt{s_{\mathrm{NN}}}=5.023\,\mathrm{Te\!V}$
$v_{3}\{2\}$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Pb}-\mathrm{Pb}$ at $\sqrt{s_{\mathrm{NN}}}=5.023\,\mathrm{Te\!V}$
$v_{4}\{2\}$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Pb}-\mathrm{Pb}$ at $\sqrt{s_{\mathrm{NN}}}=5.023\,\mathrm{Te\!V}$
Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}} = 5.02$ TeV and the corresponding nuclear modification factor $R_{\rm pPb}^{\rm ch\,jet}$ are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region $|\eta_{\rm jet}| < 0.5$ from charged particles using the anti-$k_{\rm T}$ algorithm with resolution parameters $R = 0.2$, 0.3, and 0.4. The $p_{\rm T}$-differential inclusive production cross section of charged-particle jets, as well as the corresponding cross-section ratios, are reported for pp and p-Pb collisions in the transverse momentum range $10 < p^{\rm ch}_{\rm T,jet} < 140$ GeV/$c$ and $10 < p^{\rm ch}_{\rm T,jet} < 160$ GeV/$c$, respectively, together with the nuclear modification factor $R_{\rm pPb}^{\rm ch\,jet}$ in the range $10 < p^{\rm ch}_{\rm T,jet} < 140$ GeV/$c$. The analysis extends the $p_{\rm T}$ range of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD POWHEG calculations with parton shower provided by PYTHIA8 as well as by JETSCAPE simulations.
$p_{\rm T}$-differential cross section of charged-particle jets with $R = 0.2$, $0.3$ and $0.4$ in pp collisions at $\sqrt{s} = 5.02$ TeV.
$p_{\rm T}$-differential cross section of charged-particle jets from model predictions in pp collisions at $\sqrt{s} = 5.02$ TeV.
$p_{\rm T}$-differential cross section of charged-particle jets with $R = 0.2$, $0.3$ and $0.4$ in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
In this Letter, the first measurement of the inelastic cross section for antitriton$-$nucleus interactions is reported, covering the momentum range of $0.8 \leq p < 2.4$ GeV/$c$. The measurement is carried out using data recorded with the ALICE detector in pp and Pb$-$Pb collisions at a centre-of-mass energy per nucleon of 13 TeV and 5.02 TeV, respectively. The detector material serves as an absorber for antitriton nuclei. The raw yield of (anti)triton nuclei measured with the ALICE apparatus is compared to the results from detailed ALICE simulations based on the GEANT4 toolkit for the propagation of (anti)particles through matter, allowing one to quantify the inelastic interaction probability in the detector material. This analysis complements the measurement of the inelastic cross section of antinuclei up to $A=3$ carried out by the ALICE Collaboration, and demonstrates the feasibility of the study of the isospin dependence of inelastic interaction cross section with the analysis techniques presented in this Letter.
Raw primary antitriton-to-triton ratio as a function of the momentum p_primary in exp. data.
Raw primary antitriton-to-triton ratio as a function of the momentum p_primary in MC (sigma_inel x 0.75).
Raw primary antitriton-to-triton ratio as a function of the momentum p_primary in MC (sigma_inel x 1.0).
The cross section for coherent photonuclear production of J/$\psi$ is presented as a function of the electromagnetic dissociation (EMD) of Pb. The measurement is performed with the ALICE detector in ultra-peripheral Pb-Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Cross sections are presented in five different J/$\psi$ rapidity ranges within $|y|<4$, with the J/$\psi$ reconstructed via its dilepton decay channels. In some events the J/$\psi$ is not accompanied by EMD, while other events do produce neutrons from EMD at beam rapidities either in one or the other beam direction, or in both. The cross sections in a given rapidity range and for different configurations of neutrons from EMD allow for the extraction of the energy dependence of this process in the range $17 < W_{\gamma\, \mathrm{Pb, n}} <920$ GeV, where $W_{\gamma\, \mathrm{Pb, n}}$ is the centre-of-mass energy per nucleon of the $\gamma\,\mathrm{Pb}$ system. This range corresponds to a Bjorken-$x$ interval spanning about three orders of magnitude: $ 1.1\times10^{-5}<x<3.3\times 10^{-2}$. In addition to the ultra-peripheral and photonuclear cross sections, the nuclear suppression factor is obtained. These measurements point to a strong depletion of the gluon distribution in Pb nuclei over a broad, previously unexplored, energy range. These results, together with previous ALICE measurements, provide unprecedented information to probe quantum chromodynamics at high energies.
Measured coherent J/psi cross section for the 0N0N class. Note that for each rapidity range the 0n0n uncertainty related to migrations is preceded by a ∓, while the other neutron classes have a ±; this means that these uncertainties are anti-correlated.
Measured coherent J/psi cross section for the 0NXN+XN0N class. Note that for each rapidity range the 0n0n uncertainty related to migrations is preceded by a ∓, while the other neutron classes have a ±; this means that these uncertainties are anti-correlated.
Measured coherent J/psi cross section for the XN0N forward class. Note that for each rapidity range the 0n0n uncertainty related to migrations is preceded by a ∓, while the other neutron classes have a ±; this means that these uncertainties are anti-correlated.
The interaction between $\Lambda$ baryons and kaons/antikaons is a crucial ingredient for the strangeness $S=0$ and $S=-2$ sector of the meson$-$baryon interaction at low energies. In particular, the $\Lambda{\mathrm{\overline{K}}}$ might help in understanding the origin of states such as the $\Xi\mathrm{(1620)}$, whose nature and properties are still under debate. Experimental data on $\Lambda$$-$${\mathrm{K}}$ and $\Lambda$$-$${\mathrm{\overline{K}}}$ systems are scarce, leading to large uncertainties and tension between the available theoretical predictions constrained by such data. In this Letter we present the measurements of $\Lambda$$-$K$^+\oplus \overline{\Lambda}$$-$K$^-$ and $\Lambda$$-$K$^-\oplus \overline{\Lambda}$$-$K$^+$ correlations obtained in the high-multiplicity triggered data sample in pp collisions at $\sqrt{s}=13$ TeV recorded by ALICE at the LHC. The correlation function for both pairs is modeled using the Lednicky$-$Lyuboshits analytical formula and the corresponding scattering parameters are extracted. The $\Lambda$$-$K$^-\oplus \overline{\Lambda}$$-$K$^+$ correlations show the presence of several structures at relative momenta $k^*$ above 200 MeV/$c$, compatible with the $\Omega$ baryon, the $\Xi\mathrm{(1690)}$, and $\Xi\mathrm{(1820)}$ resonances decaying into $\Lambda$$-$K$^-$ pairs. The low $k^*$ region in the $\Lambda$$-$K$^-\oplus \overline{\Lambda}$$-$K$^+$ also exhibits the presence of the $\Xi\mathrm{(1620)}$ state, expected to strongly couple to the measured pair. The presented data allow to access the $\Lambda$K$^+$ and $\Lambda$K$^-$ strong interaction with an unprecedented precision and deliver the first experimental observation of the $\Xi\mathrm{(1620)}$ decaying into $\Lambda$K$^-$.
$\Lambda K^{-}$ correlation function in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.
$\Lambda K^{+}$ correlation function in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.
$C_{background}$ correlation for $\Lambda K^{+}$ correlation function in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.
The first measurement of the cross section for incoherent photonuclear production of J/$\psi$ vector meson as a function of the Mandelstam $|t|$ variable is presented. The measurement was carried out with the ALICE detector at midrapidity, $|y|<0.8$, using ultra-peripheral collisions of Pb nuclei at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV. This rapidity interval corresponds to a Bjorken-$x$ range $(0.3$$-$$1.4)\times 10^{-3}$. Cross sections are reported in five $|t|$ intervals in the range $0.04<|t|<1$~GeV$^2$ and compared to the predictions of different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a $|t|$-dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data.
|t|-dependence of incoherent J/Psi photonuclear production cross section in Pb-Pb UPCs measured at midrapidity, |y| < 0.8
The ALICE Collaboration reports three measurements in ultra-peripheral proton$-$lead collisions at forward rapidity. The exclusive two-photon process \ggmm and the exclusive photoproduction of J/$\psi$ are studied. J/$\psi$ photoproduction with proton dissociation is measured for the first time at a hadron collider. The cross section for the two-photon process of dimuons in the invariant mass range from 1 to 2.5 GeV/$c^2$ agrees with leading order quantum electrodynamics calculations. The exclusive and dissociative cross sections for J/$\psi$ photoproductions are measured for photon$-$proton centre-of-mass energies from 27 to 57 GeV. They are in good agreement with HERA results.
Differential cross sections DSIGMA/DM for exclusive GAMMA* GAMMA* to MU+ MU- production in p–Pb UPCs for each mass and rapidity interval
Exclusive J/psi photoproduction cross section in p-Pb UPC.
Dissociative J/psi photoproduction cross section in p-Pb UPC.
Global polarizations ($P$) of $\Lambda$ ($\bar{\Lambda}$) hyperons have been observed in non-central heavy-ion collisions. The strong magnetic field primarily created by the spectator protons in such collisions would split the $\Lambda$ and $\bar{\Lambda}$ global polarizations ($\Delta P = P_{\Lambda} - P_{\bar{\Lambda}} < 0$). Additionally, quantum chromodynamics (QCD) predicts topological charge fluctuations in vacuum, resulting in a chirality imbalance or parity violation in a local domain. This would give rise to an imbalance ($\Delta n = \frac{N_{\text{L}} - N_{\text{R}}}{\langle N_{\text{L}} + N_{\text{R}} \rangle} \neq 0$) between left- and right-handed $\Lambda$ ($\bar{\Lambda}$) as well as a charge separation along the magnetic field, referred to as the chiral magnetic effect (CME). This charge separation can be characterized by the parity-even azimuthal correlator ($\Delta\gamma$) and parity-odd azimuthal harmonic observable ($\Delta a_{1}$). Measurements of $\Delta P$, $\Delta\gamma$, and $\Delta a_{1}$ have not led to definitive conclusions concerning the CME or the magnetic field, and $\Delta n$ has not been measured previously. Correlations among these observables may reveal new insights. This paper reports measurements of correlation between $\Delta n$ and $\Delta a_{1}$, which is sensitive to chirality fluctuations, and correlation between $\Delta P$ and $\Delta\gamma$ sensitive to magnetic field in Au+Au collisions at 27 GeV. For both measurements, no correlations have been observed beyond statistical fluctuations.
Figure 1
Figure 2ab
Figure 2c
The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ion collisions enables the exploration of the fundamental properties of matter under extreme conditions. Non-central collisions can produce strong magnetic fields on the order of $10^{18}$ Gauss, which offers a probe into the electrical conductivity of the QGP. In particular, quarks and anti-quarks carry opposite charges and receive contrary electromagnetic forces that alter their momenta. This phenomenon can be manifested in the collective motion of final-state particles, specifically in the rapidity-odd directed flow, denoted as $v_1(\mathsf{y})$. Here we present the charge-dependent measurements of $dv_1/d\mathsf{y}$ near midrapidities for $\pi^{\pm}$, $K^{\pm}$, and $p(\bar{p})$ in Au+Au and isobar ($_{44}^{96}$Ru+$_{44}^{96}$Ru and $_{40}^{96}$Zr+$_{40}^{96}$Zr) collisions at $\sqrt{s_{\rm NN}}=$ 200 GeV, and in Au+Au collisions at 27 GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The combined dependence of the $v_1$ signal on collision system, particle species, and collision centrality can be qualitatively and semi-quantitatively understood as several effects on constituent quarks. While the results in central events can be explained by the $u$ and $d$ quarks transported from initial-state nuclei, those in peripheral events reveal the impacts of the electromagnetic field on the QGP. Our data put valuable constraints on the electrical conductivity of the QGP in theoretical calculations.
Directed flow of $p$ and $\bar{p}$ vs rapidity in Au+Au 200 GeV 50-80% centrality.
Directed flow of $p$ and $\bar{p}$ vs rapidity in Zr+Zr and Ru+Ru 200 GeV (combined) 50-80% centrality.
Directed flow of $p$ and $\bar{p}$ vs rapidity in Au+Au 27 GeV 50-80% centrality.
Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at $\sqrt{s} = 13$ TeV at midrapidity with the ALICE detector are presented down to a transverse momentum ($p_{\rm T}$) of 0.2 GeV$/c$ and up to $p_{\rm T} = 35$ GeV$/c$, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p$-$Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the $p_{\rm T}$ range $0.5 < p_{\rm T} < 26$ GeV$/c$ at $\sqrt{s_{\rm NN}} = 8.16$ TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p$-$Pb collisions grow faster than linear with the self-normalised multiplicity. A strong $p_{\rm T}$ dependence is observed in pp collisions, where the yield of high-$p_{\rm T}$ electrons increases faster as a function of multiplicity than the one of low-$p_{\rm T}$ electrons. The measurement in p$-$Pb collisions shows no $p_{\rm T}$ dependence within uncertainties. The self-normalised yields in pp and p$-$Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations.
pT-differential cross section of electrons from heavy-flavour hadron decays in pp collisions at $\sqrt{s}$ = 13 TeV measured at midrapidity
pT-differential cross section of electrons from heavy-flavour hadron decays in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV measured at midrapidity
The Nuclear modification factor RpPb of electrons from heavy-flavour hadron decays in p--Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV
The production cross section of inclusive J/$\psi$ pairs in pp collisions at a centre-of-mass energy $\sqrt{s} = 13$ TeV is measured with ALICE. The measurement is performed for J/$\psi$ in the rapidity interval $2.5 < y < 4.0$ and for transverse momentum $p_{\rm T} > 0$. The production cross section of inclusive J/$\psi$ pairs is reported to be $10.3 \pm 2.3 {\rm (stat.)} \pm 1.3 {\rm (syst.)}$ nb in this kinematic interval. The contribution from non-prompt J/$\psi$ (i.e. originated from beauty-hadron decays) to the inclusive sample is evaluated. The results are discussed and compared with data.
Inclusive JPSI pair cross section in $2.5 < y < 4.0$.
The interactions of kaons (K) and antikaons ($\mathrm{\overline{K}}$) with few nucleons (N) were studied so far using kaonic atom data and measurements of kaon production and interaction yields in nuclei. Some details of the three-body KNN and $\mathrm{\overline{K}}$NN dynamics are still not well understood, mainly due to the overlap with multi-nucleon interactions in nuclei. An alternative method to probe the dynamics of three-body systems with kaons is to study the final state interaction within triplet of particles emitted in pp collisions at the Large Hadron Collider, which are free from effects due to the presence of bound nucleons. This Letter reports the first femtoscopic study of p$-$p$-$K$^+$ and p$-$p$-$K$^-$ correlations measured in high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV by the ALICE Collaboration. The analysis shows that the measured p$-$p$-$K$^+$ and p$-$p$-$K$^-$ correlation functions can be interpreted in terms of pairwise interactions in the triplets, indicating that the dynamics of such systems is dominated by the two-body interactions without significant contributions from three-body effects or bound states.
The (p-p)-K$^+$ correlation function obtained using the data-driven approach.
The p-(p-K$^+$) correlation function obtained using the data-driven approach.
Lower-order contributions to the p-p-K$^+$ correlation function obtained using the data-driven approach.
The measurements of the inclusive J/$\psi$ yield at midrapidity ($\left | y \right | < 0.9$) and forward rapidity (2.5 $< y <$ 4) in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC are reported. The inclusive J/$\psi$ production yields and nuclear modification factors, $R_{\rm AA}$, are measured as a function of the collision centrality, J/$\psi$ transverse momentum ($p_{\rm T}$), and rapidity. The J/$\psi$ average transverse momentum and squared transverse momentum ($\langle p_{\mathrm{T}}\rangle$ and $\langle p_{\mathrm{T}}^{\mathrm{2}}\rangle$) are evaluated as a function of the centrality at midrapidity. Compared to the previous ALICE publications, here the entire Pb$-$Pb collisions dataset collected during the LHC Run 2 is used, which improves the precision of the measurements and extends the $p_{\rm T}$ coverage. The $p_{\rm T}$-integrated $R_{\rm AA}$ shows a hint of an increasing trend towards unity from semicentral to central collisions at midrapidity, while it is flat at forward rapidity. The $p_{\rm T}$-differential $R_{\rm AA}$ shows a strong suppression at high $p_{\rm T}$ with less suppression at low $p_{\rm T}$ where it reaches a larger value at midrapidity compared to forward rapidity. The ratio of the $p_{\rm T}$-integrated yields of J/$\psi$ to those of D$^{0}$ mesons is reported for the first time for the central and semicentral event classes at midrapidity. Model calculations implementing charmonium production via the coalescence of charm quarks and antiquarks during the fireball evolution (transport models) or in a statistical approach with thermal weights are in good agreement with the data at low $p_{\rm T}$. At higher $p_{\rm T}$, the data are well described by transport models and a model based on energy loss in the strongly-interacting medium produced in nuclear collisions at the LHC.
Inclusive J$/psi$ invariant yield as a function of pT in Pb-Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV for 0-10% centrality interval and |y|< 0.9. The given systematic uncertainties are the total systematic ones and are mostly considered as fully correlated over pT.;
Inclusive J$/psi$ invariant yield as a function of pT in Pb-Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV for 30-50% centrality interval and |y|< 0.9. The given systematic uncertainties are the total systematic ones and are mostly considered as fully correlated over pT.;
Inclusive J$/psi$ invariant yield as a function of pT in Pb-Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV for 0-20% centrality interval and 2.5 < y < 4. The given systematic uncertainties are the total systematic ones. It contains the correlated uncertainties over pT which amount to 1.69%. ;
The correlations between different moments of two flow amplitudes, extracted with the recently developed asymmetric cumulants, are measured in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV recorded by the ALICE detector at the CERN Large Hadron Collider. The magnitudes of the measured observables show a dependence on the different moments as well as on the collision centrality, indicating the presence of non-linear response in all even moments up to the eighth. Furthermore, the higher-order asymmetric cumulants show different signatures than the symmetric and lower-order asymmetric cumulants. Comparisons with state-of-the-art event generators using two different parametrizations obtained from Bayesian optimization show differences between data and simulations in many of the studied observables, indicating a need for further tuning of the models behind those event generators. These results provide new and independent constraints on the initial conditions and transport properties of the system created in heavy-ion collisions.
Centrality dependence of ${\rm SC}(2,3)$ in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
Centrality dependence of ${\rm AC}_{2,1}(2,3)$ in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
Centrality dependence of ${\rm AC}_{1,2}(2,3)$ in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
The polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild $p_T$ dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagree with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and $p_T$ dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy.
$sgn(\alpha_H)\langle\cos(\theta_p^{\ast})\rangle$ of $\Lambda$ and $\bar{\Lambda}$ as a function of hyperon azimuthal angle relative to the second-order event plane in isobar collisions at 200 GeV.
$sgn(\alpha_H)\langle\cos(\theta_p^{\ast})\rangle$ of $\Lambda$ and $\bar{\Lambda}$ as a function of hyperon azimuthal angle relative to the third-order event plane in isobar collisions at 200 GeV.
$P_z$ sine coefficients of $\Lambda+\bar{\Lambda}$ as a function of centrality in isobar collisions at 200 GeV.
We report a new measurement of the production of electrons from open heavy-flavor hadron decays (HFEs) at mid-rapidity ($|y|<$ 0.7) in Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Invariant yields of HFEs are measured for the transverse momentum range of $3.5 < p_{\rm T} < 9$ GeV/$c$ in various configurations of the collision geometry. The HFE yields in head-on Au+Au collisions are suppressed by approximately a factor of 2 compared to that in $p$+$p$ collisions scaled by the average number of binary collisions, indicating strong interactions between heavy quarks and the hot and dense medium created in heavy-ion collisions. Comparison of these results with models provides additional tests of theoretical calculations of heavy quark energy loss in the quark-gluon plasma.
Ratios of NPE (non-photonic electron) to PHE (photonic electron) as a function of $p_{\rm T}$ in 0-10% central (yellow circles) and 40-80% peripheral (green squares) Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Vertical bars represent statistical uncertainties while boxes represent systematic uncertainties. Horizontal bars indicate the bin width.
Invariant yields of electrons from decays of prompt $J/\psi$ (dot-dashed line), $\Upsilon$ (dotted line), Drell-Yan (long dash-dotted line), light vector mesons (long dashed line) and the combined HDE (hadron decayed electron) contribution (solid line), estimated utilizing experimental measurements, theoretical calculations, and PYTHIA and $\rm E_{VT}G_{EN}$ event generators, in 0-10% central Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Color bands represent systematic uncertainties.
Invariant yields of electrons from decays of prompt $J/\psi$ (dot-dashed line), $\Upsilon$ (dotted line), Drell-Yan (long dash-dotted line), light vector mesons (long dashed line) and the combined HDE (hadron decayed electron) contribution (solid line), estimated utilizing experimental measurements, theoretical calculations, and PYTHIA and $\rm E_{VT}G_{EN}$ event generators, in 40-80% central Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Color bands represent systematic uncertainties.
A search for pair-produced scalar or vector leptoquarks decaying into a $b$-quark and a $\tau$-lepton is presented using the full LHC Run 2 (2015-2018) data sample of 139 fb$^{-1}$ collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} =13$ TeV. Events in which at least one $\tau$-lepton decays hadronically are considered, and multivariate discriminants are used to extract the signals. No significant deviations from the Standard Model expectation are observed and 95% confidence-level upper limits on the production cross-section are derived as a function of leptoquark mass and branching ratio $B$ into a $\tau$-lepton and $b$-quark. For scalar leptoquarks, masses below 1460 GeV are excluded assuming $B=100$%, while for vector leptoquarks the corresponding limit is 1650 GeV (1910 GeV) in the minimal-coupling (Yang-Mills) scenario.
Acceptance $\times$ efficiency for the $\tau_\text{lep}\tau_\text{had}$ signal region assuming $\beta$ = 0.5 as a function of m$_\text{LQ}$.
Acceptance $\times$ efficiency for the $\tau_\text{had}\tau_\text{had}$ signal region assuming $\beta$ = 0.5 as a function of m$_\text{LQ}$.
The observed and expected 95% CL upper limits on the scalar LQ pair production cross-sections assuming B = 1 as a function of m$_\text{LQ}$.
The azimuthal ($\Delta\varphi$) correlation distributions between heavy-flavor decay electrons and associated charged particles are measured in pp and p$-$Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV. Results are reported for electrons with transverse momentum $4<p_{\rm T}<16$ GeV/$c$ and pseudorapidity $|\eta|<0.6$. The associated charged particles are selected with transverse momentum $1<p_{\rm T}<7$ GeV/$c$, and relative pseudorapidity separation with the leading electron $|\Delta\eta| < 1$. The correlation measurements are performed to study and characterize the fragmentation and hadronization of heavy quarks. The correlation structures are fitted with a constant and two von Mises functions to obtain the baseline and the near- and away-side peaks, respectively. The results from p$-$Pb collisions are compared with those from pp collisions to study the effects of cold nuclear matter. In the measured trigger electron and associated particle kinematic regions, the two collision systems give consistent results. The $\Delta\varphi$ distribution and the peak observables in pp and p$-$Pb collisions are compared with calculations from various Monte Carlo event generators.
$\Delta\varphi$ distribution between heavy-flavor decay electrons and associated charged particles for $4 < p_{\rm T}^{\rm e} < 12$ ${\rm GeV}/c$ and $1 < p_{\rm T}^{\rm assoc} < 7$ ${\rm GeV}/c$ in pp collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV. The publication shows $\Delta\varphi$ distribution only for the ranges $1 < p_{\rm T}^{\rm assoc} < 2$, $2 < p_{\rm T}^{\rm assoc} < 3$, and $5 < p_{\rm T}^{\rm assoc} < 7$ ${\rm GeV}/c$.
$\Delta\varphi$ distribution between heavy-flavor decay electrons and associated charged particles for $4 < p_{\rm T}^{\rm e} < 12$ ${\rm GeV}/c$ and $1 < p_{\rm T}^{\rm assoc} < 7$ ${\rm GeV}/c$ in p$\textendash$Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV. The publication shows $\Delta\varphi$ distribution only for the ranges $1 < p_{\rm T}^{\rm assoc} < 2$, $2 < p_{\rm T}^{\rm assoc} < 3$, and $5 < p_{\rm T}^{\rm assoc} < 7$ ${\rm GeV}/c$.
Baseline of $\Delta\varphi$ distribution between heavy-flavor decay electrons and associated charged particles for $4 < p_{\rm T}^{\rm e} < 12$ ${\rm GeV}/c$ in pp and p$\textendash$Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV. The publication shows $\Delta\varphi$ distribution only for the ranges $1 < p_{\rm T}^{\rm assoc} < 2$, $2 < p_{\rm T}^{\rm assoc} < 3$, and $5 < p_{\rm T}^{\rm assoc} < 7$ ${\rm GeV}/c$.
A new, more precise measurement of the $\Lambda$ hyperon lifetime is performed using a large data sample of Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with ALICE. The $\Lambda$ and $\overline{\Lambda}$ hyperons are reconstructed at midrapidity using their two-body weak decay channel $\Lambda \rightarrow \mathrm{p} + \pi^{-}$ and $\overline{\Lambda} \rightarrow \overline{\mathrm{p}} + \pi^{+}$. The measured value of the $\Lambda$ lifetime is $\tau_{\Lambda} = [261.07 \pm 0.37 \ ( \rm stat.) \pm 0.72 \ (\rm syst.) ]\ \rm ps$. The relative difference between the lifetime of $\Lambda$ and $\overline{\Lambda}$, which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value $(\tau_{\Lambda}-\tau_{\overline{\Lambda}})/\tau_{\Lambda} = 0.0013 \pm 0.0028 \ (\mathrm{stat.}) \pm 0.0021 \ (\mathrm{syst.})$ is consistent with zero within the uncertainties. Both measurements of the $\Lambda$ hyperon lifetime and of the relative difference between $\tau_{\Lambda}$ and $\tau_{\overline{\Lambda}}$ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise.
Lproper spectrum of Lambda and exponential fit for the lifetime extraction. Only statistical uncertainties are shown for each data point and for the mean lifetime extracted from the exponential fit.
Lproper spectrum of Antilambda and exponential fit for the lifetime extraction. Only statistical uncertainties are shown for each data point and for the mean lifetime extracted from the exponential fit.
Lproper spectrum of Lambda and Antilambda and exponential fit for the lifetime extraction. Only statistical uncertainties are shown for each data point and for the mean lifetime extracted from the exponential fit.
A study of multiplicity and pseudorapidity distributions of inclusive photons measured in pp and p$-$Pb collisions at a center-of-mass energy per nucleon$-$nucleon collision of $\sqrt{s_{\rm NN}} = 5.02$ TeV using the ALICE detector in the forward pseudorapidity region $2.3 < \eta_{\rm lab} < 3.9$ is presented. Measurements in p$-$Pb collisions are reported for two beam configurations in which the directions of the proton and lead ion beam were reversed. The pseudorapidity distributions in p$-$Pb collisions are obtained for seven centrality classes which are defined based on different event activity estimators, i.e., the charged-particle multiplicity measured at midrapidity as well as the energy deposited in a calorimeter at beam rapidity. The inclusive photon multiplicity distributions for both pp and p$-$Pb collisions are described by double negative binomial distributions. The pseudorapidity distributions of inclusive photons are compared to those of charged particles at midrapidity in \pp collisions and for different centrality classes in p$-$Pb collisions. The results are compared to predictions from various Monte Carlo event generators. None of the generators considered in this paper reproduces the inclusive photon multiplicity distributions in the reported multiplicity range. The pseudorapidity distributions are, however, better described by the same generators.
Inclusive photon multiplicity distribution measured within $2.3<\eta_{\rm lab}<3.9$ in pp collisions at $\sqrt{s} = 5020~\mathrm{GeV}$.
Inclusive photon multiplicity distribution measured within $2.3<\eta_{\rm lab}<3.9$ in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.
Inclusive photon multiplicity distribution measured within $2.3<\eta_{\rm lab}<3.9$ in Pb-p collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.
The ALICE Collaboration reports a differential measurement of inclusive jet suppression using pp and Pb$-$Pb collision data at a center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}} = 5.02$ TeV. Charged-particle jets are reconstructed using the anti-$k_{\rm T}$ algorithm with resolution parameters $R =$ 0.2, 0.3, 0.4, 0.5, and 0.6 in pp collisions and $R =$ 0.2, 0.4, 0.6 in central (0$-$10%), semi-central (30$-$50%), and peripheral (60$-$80%) Pb$-$Pb collisions. A novel approach based on machine learning is employed to mitigate the influence of jet background. This enables measurements of inclusive jet suppression in new regions of phase space, including down to the lowest jet $p_{\rm T} \geq 40$ GeV/$c$ at $R = 0.6$ in central Pb$-$Pb collisions. This is an important step for discriminating different models of jet quenching in the quark-gluon plasma. The transverse momentum spectra, nuclear modification factors, derived cross section, and nuclear modification factor ratios for different jet resolution parameters of charged-particle jets are presented and compared to model predictions. A mild dependence of the nuclear modification factor ratios on collision centrality and resolution parameter is observed. The results are compared to a variety of jet-quenching models with varying levels of agreement.
delta pT distributions for ML and AB methods in central collisions with R = 0.4.
Summary of standard deviation of delta pT distributions for ML and AB methods in central and semi-central collisions as a function of the jet resolution parameter.
Raa toy distributions for charged jets as a function of jet pT for fractional in cone, fractional out of cone, and medium response toy modifications.
The fractions of non-prompt (i.e. originating from beauty-hadron decays) D$^0$ and D$^+$ mesons with respect to the inclusive yield are measured as a function of the charged-particle multiplicity in proton$-$proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV with the ALICE detector at the LHC. The results are reported in intervals of transverse momentum ($p_{\rm T}$) and integrated in the range $1 < p_{\rm T} < 24$ GeV/$c$. The fraction of non-prompt D$^0$ and D$^+$ mesons is found to increase slightly as a function of $p_{\rm T}$ in all the measured multiplicity intervals, while no significant dependence on the charged-particle multiplicity is observed. In order to investigate the production and hadronisation mechanisms of charm and beauty quarks, the results are compared to PYTHIA 8 as well as EPOS 3 and EPOS 4 Monte Carlo simulations, and to calculations based on the colour glass condensate including three-pomeron fusion.
This paper presents direct searches for lepton flavour violation in Higgs boson decays, $H\rightarrow e\tau$ and $H\rightarrow\mu\tau$, performed using data collected with the ATLAS detector at the LHC. The searches are based on a data sample of proton-proton collisions at a centre-of-mass energy $\sqrt{s} = 13$ TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. Leptonic ($\tau \rightarrow \ell \nu_\ell \nu_\tau$) and hadronic ($\tau \rightarrow $ hadrons $ \nu_\tau$) decays of the $\tau$-lepton are considered. Two background estimation techniques are employed: the MC-template method, based on data-corrected simulation samples, and the Symmetry method, based on exploiting the symmetry between electrons and muons in the Standard Model backgrounds. No significant excess of events is observed and the results are interpreted as upper limits on lepton-flavour-violating branching ratios of the Higgs boson. The observed (expected) upper limits set on the branching ratios at 95% confidence level, $\mathcal{B}(H\rightarrow e\tau)<0.20\%$ (0.12%) and $\mathcal{B}(H\rightarrow \mu\tau)<0.18\%$ (0.09%), are obtained with the MC-template method from a simultaneous measurement of potential $H \rightarrow e\tau$ and $H \rightarrow\mu\tau$ signals. The best-fit branching ratio difference, $\mathcal{B}(H\rightarrow \mu\tau)- \mathcal{B}(H\rightarrow e\tau)$, measured with the Symmetry method in the channel where the $\tau$-lepton decays to leptons, is (0.25 $\pm$ 0.10)%, compatible with a value of zero within 2.5$\sigma$.
Fit results of the simultaneous measurements of the $H\to e\tau$ and $H\to \mu\tau$ signals (2POI) showing upper limits at 95% C.L. on the LFV branching ratios of the Higgs boson $H\to e\tau$. The results from standalone channel/categories fits are compared with the results of the combined fit.
Fit results of the simultaneous measurements of the $H\to e\tau$ and $H\to \mu\tau$ signals (2POI) showing upper limits at 95% C.L. on the LFV branching ratios of the Higgs boson $H\to e\tau$. The results from standalone channel/categories fits are compared with the results of the combined fit.
Fit results of the simultaneous measurements of the $H\to e\tau$ and $H\to \mu\tau$ signals (2POI) showing best-fit values of the LFV branching ratios of the Higgs boson $\hat{B}$($H\to e\tau$). The results from standalone channel/categories fits are compared with the results of the combined fit.
Measurements of the suppression and correlations of dijets is performed using 3 $\mu$b$^{-1}$ of Xe+Xe data at $\sqrt{s_{\mathrm{NN}}} = 5.44$ TeV collected with the ATLAS detector at the LHC. Dijets with jets reconstructed using the $R=0.4$ anti-$k_t$ algorithm are measured differentially in jet $p_{\text{T}}$ over the range of 32 GeV to 398 GeV and the centrality of the collisions. Significant dijet momentum imbalance is found in the most central Xe+Xe collisions, which decreases in more peripheral collisions. Results from the measurement of per-pair normalized and absolutely normalized dijet $p_{\text{T}}$ balance are compared with previous Pb+Pb measurements at $\sqrt{s_{\mathrm{NN}}} =5.02$ TeV. The differences between the dijet suppression in Xe+Xe and Pb+Pb are further quantified by the ratio of pair nuclear-modification factors. The results are found to be consistent with those measured in Pb+Pb data when compared in classes of the same event activity and when taking into account the difference between the center-of-mass energies of the initial parton scattering process in Xe+Xe and Pb+Pb collisions. These results should provide input for a better understanding of the role of energy density, system size, path length, and fluctuations in the parton energy loss.
The centrality intervals in Xe+Xe collisions and their corresponding TAA with absolute uncertainties.
The centrality intervals in Xe+Xe and Pb+Pb collisions for matching SUM ET FCAL intervals and respective TAA values for Xe+Xe collisions.
The performance of the jet energy scale (JES) for jets with $|y| < 2.1$ evaluated as a function of pT_truth in different centrality bins. Simulated hard scatter events were overlaid onto events from a dedicated sample of minimum-bias Xe+Xe data.
This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb$^{-1}$ of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688 $\pm$ 23 (stat.) $^{+75}_{-71}$ (syst.) fb, to be compared with the standard model prediction of 515 $^{+36}_{-42}$ fb at next-to-leading order in QCD.
This table shows the values for $\sigma_{tq\gamma}\times\mathcal{B}(t\rightarrow l\nu b)$ and $\sigma_{tq\gamma}\times\mathcal{B}(t\rightarrow l\nu b)+\sigma_{t(\rightarrow l\nu b\gamma)q}$ obtained by a profile-likelihood fit in the fiducial parton-level phase space (defined in Table 1) and particle-level phase space (defined in Table 2), respectively.
Distribution of the reconstructed top-quark mass in the $W\gamma\,$CR before the profile-likelihood fit. The "Total" column corresponds to the sum of the expected contributions from the signal and background processes. The uncertainty represents the sum of statistical and systematic uncertainties in the signal and background predictions. The first and last bins include the underflow and overflow, respectively.
Distribution of the NN output in the 0fj$\,$SR in data and the expected contribution of the signal and background processes after the profile-likelihood fit. The "Total" column corresponds to the sum of the expected contributions from the signal and background processes. The uncertainty represents the sum of statistical and systematic uncertainties in the signal and background predictions considering the correlations of the uncertainties as obtained by the fit.
A newly developed observable for correlations between symmetry planes, which characterize the direction of the anisotropic emission of produced particles, is measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV with ALICE. This so-called Gaussian Estimator allows for the first time the study of these quantities without the influence of correlations between different flow amplitudes. The centrality dependence of various correlations between two, three and four symmetry planes is presented. The ordering of magnitude between these symmetry plane correlations is discussed and the results of the Gaussian Estimator are compared with measurements of previously used estimators. The results utilizing the new estimator lead to significantly smaller correlations than reported by studies using the Scalar Product method. Furthermore, the obtained symmetry plane correlations are compared to state-of-the-art hydrodynamic model calculations for the evolution of heavy-ion collisions. While the model predictions provide a qualitative description of the data, quantitative agreement is not always observed, particularly for correlators with significant non-linear response of the medium to initial state anisotropies of the collision system. As these results provide unique and independent information, their usage in future Bayesian analysis can further constrain our knowledge on the properties of the QCD matter produced in ultrarelativistic heavy-ion collisions.
Centrality dependence of $\langle \cos[4(\Psi_{4}-\Psi_{2})]\rangle_{\mathrm{GE}}$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.
Centrality dependence of $\langle \cos[6(\Psi_{6}-\Psi_{3})]\rangle_{\mathrm{GE}}$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.
Centrality dependence of $\langle \cos[6(\Psi_{2}-\Psi_{3})]\rangle_{\mathrm{GE}}$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.
Measurements of differential cross sections are presented for inclusive isolated-photon production in $pp$ collisions at a centre-of-mass energy of 13 TeV provided by the LHC and using 139 fb$^{-1}$ of data recorded by the ATLAS experiment. The cross sections are measured as functions of the photon transverse energy in different regions of photon pseudorapidity. The photons are required to be isolated by means of a fixed-cone method with two different cone radii. The dependence of the inclusive-photon production on the photon isolation is investigated by measuring the fiducial cross sections as functions of the isolation-cone radius and the ratios of the differential cross sections with different radii in different regions of photon pseudorapidity. The results presented in this paper constitute an improvement with respect to those published by ATLAS earlier: the measurements are provided for different isolation radii and with a more granular segmentation in photon pseudorapidity that can be exploited in improving the determination of the proton parton distribution functions. These improvements provide a more in-depth test of the theoretical predictions. Next-to-leading-order QCD predictions from JETPHOX and SHERPA and next-to-next-to-leading-order QCD predictions from NNLOJET are compared to the measurements, using several parameterisations of the proton parton distribution functions. The measured cross sections are well described by the fixed-order QCD predictions within the experimental and theoretical uncertainties in most of the investigated phase-space region.
Measured cross sections for inclusive isolated-photon production as a function of $E_{\rm T}^{\gamma}$ for $|\eta^{\gamma}|<0.6$ and photon isolation cone radius $R=0.4$.
Measured cross sections for inclusive isolated-photon production as a function of $E_{\rm T}^{\gamma}$ for $0.6<|\eta^{\gamma}|<0.8$ and photon isolation cone radius $R=0.4$.
Measured cross sections for inclusive isolated-photon production as a function of $E_{\rm T}^{\gamma}$ for $0.8<|\eta^{\gamma}|<1.37$ and photon isolation cone radius $R=0.4$.
A search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s} = 13$ TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small $R$-parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of $m(\tilde{g})=2.4$ TeV gluinos, electroweakinos with $m(\tilde\chi^0_1)=1.5$ TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.
<b>Tables of Yields:</b> <a href="?table=validation_regions_yields_highpt_SR">Validation Regions Summary Yields, High-pT jet selections</a> <a href="?table=validation_regions_yields_trackless_SR">Validiation Regions Summary Yields, Trackless jet selections</a> <a href="?table=yields_highpt_SR_observed">Signal region (and sidebands) observed yields, High-pT jet selections</a> <a href="?table=yields_highpt_SR_expected">Signal region (and sidebands) expected yields, High-pT jet selections</a> <a href="?table=yields_trackless_SR_observed">Signal region (and sidebands) observed yields, Trackless jet selections</a> <a href="?table=yields_trackless_SR_expected">Signal region (and sidebands) expected yields, Trackless jet selections</a> <b>Exclusion Contours:</b> <a href="?table=excl_ewk_exp_nominal">EWK RPV signal; expected, nominal</a> <a href="?table=excl_ewk_exp_up">EWK RPV signal; expected, $+1\sigma$</a> <a href="?table=excl_ewk_exp_down">EWK RPV signal; expected, $-1\sigma$</a> <a href="?table=excl_ewk_obs_nominal">EWK RPV signal; observed, nominal</a> <a href="?table=excl_ewk_obs_up">EWK RPV signal; observed, $+1\sigma$</a> <a href="?table=excl_ewk_obs_down">EWK RPV signal; observed, $-1\sigma$</a> <a href="?table=excl_strong_mgluino_2400_GeV_exp_nominal">Strong RPV signal, m($\tilde{g}$)=2.4 TeV; expected, nominal</a> <a href="?table=excl_strong_mgluino_2400_GeV_exp_up">Strong RPV signal, m($\tilde{g}$)=2.4 TeV; expected, $+1\sigma$</a> <a href="?table=excl_strong_mgluino_2400_GeV_exp_down">Strong RPV signal, m($\tilde{g}$)=2.4 TeV; expected, $-1\sigma$</a> <a href="?table=excl_strong_mgluino_2400_GeV_obs_nominal">Strong RPV signal, m($\tilde{g}$)=2.4 TeV; observed, nominal</a> <a href="?table=excl_strong_mgluino_2400_GeV_obs_up">Strong RPV signal, m($\tilde{g}$)=2.4 TeV; observed, $+1\sigma$</a> <a href="?table=excl_strong_mgluino_2400_GeV_obs_down">Strong RPV signal, m($\tilde{g}$)=2.4 TeV; observed, $-1\sigma$</a> <a href="?table=excl_xsec_ewk">EWK RPV signal; cross-section limits for fixed lifetime values.</a> <a href="?table=excl_xsec_strong_mgluino_2400">Strong RPV signal, m($\tilde{g}$)=2.4 TeV; cross-section limits for fixed lifetime values.</a> <a href="?table=excl_strong_mgluino_2000_GeV_exp_nominal">Strong RPV signal, m($\tilde{g}$)=2.0 TeV; expected, nominal</a> <a href="?table=excl_strong_mgluino_2000_GeV_exp_up">Strong RPV signal, m($\tilde{g}$)=2.0 TeV; expected, $+1\sigma$</a> <a href="?table=excl_strong_mgluino_2000_GeV_exp_down">Strong RPV signal, m($\tilde{g}$)=2.0 TeV; expected, $-1\sigma$</a> <a href="?table=excl_strong_mgluino_2000_GeV_obs_nominal">Strong RPV signal, m($\tilde{g}$)=2.0 TeV; observed, nominal</a> <a href="?table=excl_strong_mgluino_2000_GeV_obs_up">Strong RPV signal, m($\tilde{g}$)=2.0 TeV; observed, $+1\sigma$</a> <a href="?table=excl_strong_mgluino_2000_GeV_obs_down">Strong RPV signal, m($\tilde{g}$)=2.0 TeV; observed, $-1\sigma$</a> <a href="?table=excl_strong_mgluino_2200_GeV_exp_nominal">Strong RPV signal, m($\tilde{g}$)=2.2 TeV; expected, nominal</a> <a href="?table=excl_strong_mgluino_2200_GeV_exp_up">Strong RPV signal, m($\tilde{g}$)=2.2 TeV; expected, $+1\sigma$</a> <a href="?table=excl_strong_mgluino_2200_GeV_exp_down">Strong RPV signal, m($\tilde{g}$)=2.2 TeV; expected, $-1\sigma$</a> <a href="?table=excl_strong_mgluino_2200_GeV_obs_nominal">Strong RPV signal, m($\tilde{g}$)=2.2 TeV; observed, nominal</a> <a href="?table=excl_strong_mgluino_2200_GeV_obs_up">Strong RPV signal, m($\tilde{g}$)=2.2 TeV; observed, $+1\sigma$</a> <a href="?table=excl_strong_mgluino_2200_GeV_obs_down">Strong RPV signal, m($\tilde{g}$)=2.2 TeV; observed, $-1\sigma$</a> <a href="?table=excl_strong_mchi0_50_GeV_exp_nominal">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.1 TeV; expected, nominal</a> <a href="?table=excl_strong_mchi0_50_GeV_exp_up">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.1 TeV; expected, $+1\sigma$</a> <a href="?table=excl_strong_mchi0_50_GeV_exp_down">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.1 TeV; expected, $-1\sigma$</a> <a href="?table=excl_strong_mchi0_50_GeV_obs_nominal">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.1 TeV; observed, nominal</a> <a href="?table=excl_strong_mchi0_50_GeV_obs_up">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.1 TeV; observed, $+1\sigma$</a> <a href="?table=excl_strong_mchi0_50_GeV_obs_down">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.1 TeV; observed, $-1\sigma$</a> <a href="?table=excl_strong_mchi0_450_GeV_exp_nominal">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.5 TeV; expected, nominal</a> <a href="?table=excl_strong_mchi0_450_GeV_exp_up">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.5 TeV; expected, $+1\sigma$</a> <a href="?table=excl_strong_mchi0_450_GeV_exp_down">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.5 TeV; expected, $-1\sigma$</a> <a href="?table=excl_strong_mchi0_450_GeV_obs_nominal">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.5 TeV; observed, nominal</a> <a href="?table=excl_strong_mchi0_450_GeV_obs_up">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.5 TeV; observed, $+1\sigma$</a> <a href="?table=excl_strong_mchi0_450_GeV_obs_down">Strong RPV signal, m($\tilde{\chi}^{0}$)=0.5 TeV; observed, $-1\sigma$</a> <a href="?table=excl_strong_tau_0p01_ns_exp_nominal">Strong RPV signal, $\tau$=0.01 ns; expected, nominal</a> <a href="?table=excl_strong_tau_0p01_ns_exp_up">Strong RPV signal, $\tau$=0.01 ns; expected, $+1\sigma$</a> <a href="?table=excl_strong_tau_0p01_ns_exp_down">Strong RPV signal, $\tau$=0.01 ns; expected, $-1\sigma$</a> <a href="?table=excl_strong_tau_0p01_ns_obs_nominal">Strong RPV signal, $\tau$=0.01 ns; observed, nominal</a> <a href="?table=excl_strong_tau_0p01_ns_obs_up">Strong RPV signal, $\tau$=0.01 ns; observed, $+1\sigma$</a> <a href="?table=excl_strong_tau_0p01_ns_obs_down">Strong RPV signal, $\tau$=0.01 ns; observed, $-1\sigma$</a> <a href="?table=excl_strong_tau_0p1_ns_exp_nominal">Strong RPV signal, $\tau$=0.10 ns; expected, nominal</a> <a href="?table=excl_strong_tau_0p1_ns_exp_up">Strong RPV signal, $\tau$=0.10 ns; expected, $+1\sigma$</a> <a href="?table=excl_strong_tau_0p1_ns_exp_down">Strong RPV signal, $\tau$=0.10 ns; expected, $-1\sigma$</a> <a href="?table=excl_strong_tau_0p1_ns_obs_nominal">Strong RPV signal, $\tau$=0.10 ns; observed, nominal</a> <a href="?table=excl_strong_tau_0p1_ns_obs_up">Strong RPV signal, $\tau$=0.10 ns; observed, $+1\sigma$</a> <a href="?table=excl_strong_tau_0p1_ns_obs_down">Strong RPV signal, $\tau$=0.10 ns; observed, $-1\sigma$</a> <a href="?table=excl_strong_tau_1_ns_exp_nominal">Strong RPV signal, $\tau$=1.00 ns; expected, nominal</a> <a href="?table=excl_strong_tau_1_ns_exp_up">Strong RPV signal, $\tau$=1.00 ns; expected, $+1\sigma$</a> <a href="?table=excl_strong_tau_1_ns_exp_down">Strong RPV signal, $\tau$=1.00 ns; expected, $-1\sigma$</a> <a href="?table=excl_strong_tau_1_ns_obs_nominal">Strong RPV signal, $\tau$=1.00 ns; observed, nominal</a> <a href="?table=excl_strong_tau_1_ns_obs_up">Strong RPV signal, $\tau$=1.00 ns; observed, $+1\sigma$</a> <a href="?table=excl_strong_tau_1_ns_obs_down">Strong RPV signal, $\tau$=1.00 ns; observed, $-1\sigma$</a> <a href="?table=excl_strong_tau_10_ns_exp_nominal">Strong RPV signal, $\tau$=10.00 ns; expected, nominal</a> <a href="?table=excl_strong_tau_10_ns_exp_up">Strong RPV signal, $\tau$=10.00 ns; expected, $+1\sigma$</a> <a href="?table=excl_strong_tau_10_ns_exp_down">Strong RPV signal, $\tau$=10.00 ns; expected, $-1\sigma$</a> <a href="?table=excl_strong_tau_10_ns_obs_nominal">Strong RPV signal, $\tau$=10.00 ns; observed, nominal</a> <a href="?table=excl_strong_tau_10_ns_obs_up">Strong RPV signal, $\tau$=10.00 ns; observed, $+1\sigma$</a> <a href="?table=excl_strong_tau_10_ns_obs_down">Strong RPV signal, $\tau$=10.00 ns; observed, $-1\sigma$</a> <a href="?table=excl_xsec_strong_chi0_1250">Strong RPV signal, m($\tilde{\chi}^0_1$)=1.25 TeV; cross-section limits for fixed lifetime values.</a> <br/><b>Reinterpretation Material:</b> See the attached resource (purple button on the left) or directly <a href="https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2016-08/hepdata_info.pdf">this link</a> for information about acceptance definition and about how to use the efficiency histograms below. SLHA files are also available in the reource page of this HEPData record. <a href="?table=acceptance_highpt_strong"> Acceptance cutflow, High-pT SR, Strong production.</a> <a href="?table=acceptance_trackless_ewk"> Acceptance cutflow, Trackless SR, EWK production.</a> <a href="?table=acceptance_trackless_ewk_hf"> Acceptance cutflow, Trackless SR, EWK production with heavy-flavor.</a> <a href="?table=acceptance_highpt_ewk_hf"> Acceptance cutflow, Trackless SR, EWK production with heavy-flavor.</a> <a href="?table=event_efficiency_HighPt_R_1150_mm">Reinterpretation Material: Event-level Efficiency for HighPt SR selections, R < 1150 mm</a> <a href="?table=event_efficiency_HighPt_R_1150_3870_mm">Reinterpretation Material: Event-level Efficiency for HighPt SR selections, R [1150, 3870] mm</a> <a href="?table=event_efficiency_HighPt_R_3870_mm">Reinterpretation Material: Event-level Efficiency for HighPt SR selections, R > 3870 mm</a> <a href="?table=event_efficiency_Trackless_R_1150_mm">Reinterpretation Material: Event-level Efficiency for Trackless SR selections, R < 1150 mm</a> <a href="?table=event_efficiency_Trackless_R_1150_3870_mm">Reinterpretation Material: Event-level Efficiency for Trackless SR selections, R [1150, 3870] mm</a> <a href="?table=event_efficiency_Trackless_R_3870_mm">Reinterpretation Material: Event-level Efficiency for Trackless SR selections, R > 3870 mm</a> <a href="?table=vertex_efficiency_R_22_mm">Reinterpretation Material: Vertex-level Efficiency for R < 22 mm</a> <a href="?table=vertex_efficiency_R_22_25_mm">Reinterpretation Material: Vertex-level Efficiency for R [22, 25] mm</a> <a href="?table=vertex_efficiency_R_25_29_mm">Reinterpretation Material: Vertex-level Efficiency for R [25, 29] mm</a> <a href="?table=vertex_efficiency_R_29_38_mm">Reinterpretation Material: Vertex-level Efficiency for R [29, 38] mm</a> <a href="?table=vertex_efficiency_R_38_46_mm">Reinterpretation Material: Vertex-level Efficiency for R [38, 46] mm</a> <a href="?table=vertex_efficiency_R_46_73_mm">Reinterpretation Material: Vertex-level Efficiency for R [46, 73] mm</a> <a href="?table=vertex_efficiency_R_73_84_mm">Reinterpretation Material: Vertex-level Efficiency for R [73, 84] mm</a> <a href="?table=vertex_efficiency_R_84_111_mm">Reinterpretation Material: Vertex-level Efficiency for R [84, 111] mm</a> <a href="?table=vertex_efficiency_R_111_120_mm">Reinterpretation Material: Vertex-level Efficiency for R [111, 120] mm</a> <a href="?table=vertex_efficiency_R_120_145_mm">Reinterpretation Material: Vertex-level Efficiency for R [120, 145] mm</a> <a href="?table=vertex_efficiency_R_145_180_mm">Reinterpretation Material: Vertex-level Efficiency for R [145, 180] mm</a> <a href="?table=vertex_efficiency_R_180_300_mm">Reinterpretation Material: Vertex-level Efficiency for R [180, 300] mm</a> <br/><b>Cutflow Tables:</b> <a href="?table=cutflow_highpt_strong"> Cutflow (Acceptance x Efficiency), High-pT SR, Strong production.</a> <a href="?table=cutflow_trackless_ewk"> Cutflow (Acceptance x Efficiency), Trackless SR, EWK production.</a> <a href="?table=cutflow_trackless_ewk_hf"> Cutflow (Acceptance x Efficiency), Trackless SR, EWK production with heavy-flavor quarks.</a> <a href="?table=cutflow_highpt_ewk_hf"> Cutflow (Acceptance x Efficiency), High-pT SR, EWK production with heavy-flavor quarks.</a>
Validation of background estimate in validation regions for the High-pT jet selections
Validation of background estimate in validation regions for the Trackless jet selections
Recent measurements of charm-baryon production in hadronic collisions have questioned the universality of charm-quark fragmentation across different collision systems. In this work the fragmentation of charm quarks into charm baryons is probed, by presenting the first measurement of the longitudinal jet momentum fraction carried by $\Lambda_{\rm c}^{+}$ baryons, $z^{\mathrm{ch}}_\mathrm{||}$, in hadronic collisions. The results are obtained in proton-proton (pp) collisions at $\sqrt{s}=13$ TeV at the LHC, with $\Lambda_{\rm c}^{+}$ baryons and charged (track-based) jets reconstructed in the transverse momentum intervals of $3 \leq p_{\rm T}^{\Lambda_{\rm c}^{+}} < 15$ GeV/$c$ and $7 \leq p_{\rm T}^{\rm jet\;ch} < 15$ GeV/$c$, respectively. The $z^{\mathrm{ch}}_\mathrm{||}$ distribution is compared to a measurement of ${\rm D}^0$-tagged charged jets in pp collisions as well as to PYTHIA 8 simulations. The data hints that the fragmentation of charm quarks into charm baryons is softer with respect to charm mesons, in the measured kinematic interval, as predicted by hadronisation models which include colour correlations beyond leading-colour in the string formation.
$z_{\parallel}^{\rm{ch}}$ for $\Lambda_{\rm{c}}^{+}$-tagged jets and D$^{0}$-tagged jets in the $p_{\rm{T}}^{\rm{jet\text{ }ch}}$: 7-15 GeV/$c$ interval.
$z_{\parallel}^{\rm{ch}}$ ratio of $\Lambda_{\rm{c}}^{+}$-tagged jets and D$^{0}$-tagged jets in the $p_{\rm{T}}^{\rm{jet\text{ }ch}}$: 7-15 GeV/$c$ interval.
A search for flavor-changing neutral-current couplings between a top quark, an up or charm quark and a $Z$ boson is presented, using proton-proton collision data at $\sqrt{s} = 13$ TeV collected by the ATLAS detector at the Large Hadron Collider. The analyzed dataset corresponds to an integrated luminosity of 139 fb$^{-1}$. The search targets both single-top-quark events produced as $gq\rightarrow tZ$ (with $q = u, c$) and top-quark-pair events, with one top quark decaying through the $t \rightarrow Zq$ channel. The analysis considers events with three leptons (electrons or muons), a $b$-tagged jet, possible additional jets, and missing transverse momentum. The data are found to be consistent with the background-only hypothesis and 95% confidence-level limits on the $t \rightarrow Zq$ branching ratios are set, assuming only tensor operators of the Standard Model effective field theory framework contribute to the $tZq$ vertices. These are $6.2 \times 10^{-5}$ ($13\times 10^{-5}$) for $t\rightarrow Zu$ ($t\rightarrow Zc$) for a left-handed $tZq$ coupling, and $6.6 \times 10^{-5}$ ($12\times 10^{-5}$) in the case of a right-handed coupling. These results are interpreted as 95% CL upper limits on the strength of corresponding couplings, yielding limits for $|C_{uW}^{(13)*}|$ and $|C_{uB}^{(13)*}|$ ($|C_{uW}^{(31)}|$ and $|C_{uB}^{(31)}|$) of 0.15 (0.16), and limits for $|C_{uW}^{(23)*}|$ and $|C_{uB}^{(23)*}|$ ($|C_{uW}^{(32)}|$ and $|C_{uB}^{(32)}|$) of 0.22 (0.21), assuming a new-physics energy scale $\Lambda_\text{NP}$ of 1 TeV.
Summary of the signal strength $\mu$ parameters obtained from the fits to extract LH and RH results for the FCNC tZu and tZc couplings. For the reference branching ratio, the most stringent limits are used.
Observed and expected 95% CL limits on the FCNC $t\rightarrow Zq$ branching ratios and the effective coupling strengths for different vertices and couplings (top eight rows). For the latter, the energy scale is assumed to be $\Lambda_{NP}$ = 1 TeV. The bottom rows show, for the case of the FCNC $t\rightarrow Zu$ branching ratio, the observed and expected 95% CL limits when only one of the two SRs, either SR1 or SR2, and all CRs are included in the likelihood.
Comparison between data and background prediction before the fit (Pre-Fit) for the mass of the SM top-quark candidate in SR1. The uncertainty band includes both the statistical and systematic uncertainties in the background prediction. The four FCNC LH signals are also shown separately, normalized to five times the cross-section corresponding to the most stringent observed branching ratio limits. The first (last) bin in all distributions includes the underflow (overflow). The lower panels show the ratios of the data (Data) to the background prediction (Bkg.).
The production of $\pi^\pm$, ${\rm K}^\pm$, and $(\overline{\rm p})$p is measured in pp collisions at $\sqrt{s}=13$ TeV in different topological regions. Particle transverse momentum ($p_{\rm T}$) spectra are measured in the ``toward'', ``transverse'', and ``away'' angular regions defined with respect to the direction of the leading particle in the event. While the toward and away regions contain the fragmentation products of the near-side and away-side jets, respectively, the transverse region is dominated by particles from the Underlying Event (UE). The relative transverse activity classifier, $R_{\rm T}=N_{\rm T}/\langle N_{\rm T}\rangle$, is used to group events according to their UE activity, where $N_{\rm T}$ is the measured charged-particle multiplicity per event in the transverse region and $\langle N_{\rm T}\rangle$ is the mean value over all the analysed events. The first measurements of identified particle $p_{\rm T}$ spectra as a function of $R_{\rm T}$ in the three topological regions are reported. The yield of high transverse momentum particles relative to the $R_{\rm T}$-integrated measurement decreases with increasing $R_{\rm T}$ in both the toward and away regions, indicating that the softer UE dominates particle production as $R_{\rm T}$ increases and validating that $R_{\rm T}$ can be used to control the magnitude of the UE. Conversely, the spectral shapes in the transverse region harden significantly with increasing $R_{\rm T}$. This hardening follows a mass ordering, being more significant for heavier particles. The $p_{\rm T}$-differential particle ratios $({\rm p+\overline{p}})/(\pi^+ +\pi^-)$ and $({\rm K^+ +K^-})/(\pi^+ +\pi^-)$ in the low UE limit $(R_{\rm T}\rightarrow 0)$ approach expectations from Monte Carlo generators such as PYTHIA 8 with Monash 2013 tune and EPOS LHC, where the jet-fragmentation models have been tuned to reproduce ${\rm e^+ e^-}$ results.
$N_{\mathrm{T}}$ probability distribution in the transverse region using events with leading particles $(p_{\mathrm{T}}^{\mathrm{leading}} \geq 5~\mathrm{GeV}/c)$ in the pseudorapidity interval $|\eta|<0.8$ in pp collisions at $\sqrt{s} = 13~\mathrm{TeV}$.
$R_{\mathrm{T}}$ probability distribution in the transverse region using events with leading particles $(p_{\mathrm{T}}^{\mathrm{leading}} \geq 5~\mathrm{GeV}/c)$ in the pseudorapidity interval $|\eta|<0.8$ in pp collisions at $\sqrt{s} = 13~\mathrm{TeV}$.
$\pi^{+}+\pi^{-}$ transverse momentum spectrum for events with $0 \leq R_{\mathrm{T}} < 5$ in the Toward region in pp collisions at $\sqrt{s} = 13~\mathrm{TeV}$.
Measurements of transverse energy$-$energy correlations and their associated azimuthal asymmetries in multijet events are presented. The analysis is performed using a data sample corresponding to 139 $\mbox{fb\(^{-1}\)}$ of proton$-$proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. They are then compared to next-to-next-to-leading-order perturbative QCD calculations for the first time, which feature a significant reduction in the theoretical uncertainties estimated using variations of the renormalisation and factorisation scales. The agreement between data and theory is good, thus providing a precision test of QCD at large momentum transfers $Q$. The strong coupling constant $\alpha_s$ is extracted differentially as a function of $Q$, showing a good agreement with the renormalisation group equation and with previous analyses. A simultaneous fit to all transverse energy$-$energy correlation distributions across different kinematic regions yields a value of $\alpha_\mathrm{s}(m_Z) = 0.1175 \pm 0.0006 \mbox{ (exp.)} ^{+0.0034}_{-0.0017} \mbox{ (theo.)}$, while the global fit to the asymmetry distributions yields $\alpha_{\mathrm{s}}(m_Z) = 0.1185 \pm 0.0009 \mbox{ (exp.)} ^{+0.0025}_{-0.0012} \mbox{ (theo.)}$.
Particle-level TEEC results
Particle-level TEEC results for the first HT2 bin
Particle-level TEEC results for the second HT2 bin
This paper presents a search for a new Z' vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at $\sqrt{s} = 13$ TeV, corresponding to an integrated luminosity of 139 fb$^{-1}$. The new gauge boson Z' is predicted by $L_{\mu}-L_{\tau}$ models to address observed phenomena that can not be explained by the Standard Model. The search examines the four-muon (4$\mu$) final state, using a deep learning neural network classifier to separate the Z' signal from the Standard Model background events. The di-muon invariant masses in the $4\mu$ events are used to extract the Z' resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z' production cross-section times the decay branching fraction of $pp \rightarrow Z'\mu\mu \rightarrow 4\mu$ are set from 0.31 to 4.3 fb for the Z' mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, $g_{Z'}$, of the Z' boson to the second and third generation leptons above 0.003 - 0.2 have been excluded.
Summary of the chosen $Z'$ hypotheses and corresponding coupling, width, and cross-section (calculated at LO accuracy in QCD) at each mass point.
Summary of the chosen $Z'$ hypotheses and corresponding coupling, width, and cross-section (calculated at LO accuracy in QCD) at each mass point.
The $Z'$ signal event selection efficiencies compared to the events passing the previous cut level for several representative mass points. The overall signal efficiencies are the products of the 4$\mu$ MC filter and the combined event selection efficiencies.
A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle $X$ decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to $qX$, with $X \rightarrow b\bar{b}$, and the other top quark decays according to the Standard Model, with the $W$ boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from $b$-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction $\mathcal{B}$($t \rightarrow uX$) and between 0.018% and 0.078% for the branching fraction $\mathcal{B}$($t \rightarrow cX$), for masses of the scalar particle $X$ between 20 and 160 GeV.
Expected and observed 95% CL upper limits for $\mathcal{B}$($t \rightarrow uX$) $\times$ $\mathcal{B}$($X \rightarrow b\bar{b}$). The bands surrounding the expected limits show the 68% and 95% confidence intervals, respectively.
Expected and observed 95% CL upper limits for $\mathcal{B}$($t \rightarrow cX$) $\times$ $\mathcal{B}$($X \rightarrow b\bar{b}$). The bands surrounding the expected limits show the 68% and 95% confidence intervals, respectively.
Expected and observed 95% CL upper limits for $\mathcal{B}$($t \rightarrow uH$) $\times$ $\mathcal{B}$($X \rightarrow b\bar{b}$) and $\mathcal{B}$($t \rightarrow cH$) $\times$ $\mathcal{B}$($X \rightarrow b\bar{b}$).
A search for the leptonic charge asymmetry ($A_\text{c}^{\ell}$) of top-quark$-$antiquark pair production in association with a $W$ boson ($t\bar{t}W$) is presented. The search is performed using final states with exactly three charged light leptons (electrons or muons) and is based on $\sqrt{s} = 13$ TeV proton$-$proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN during the years 2015$-$2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. A profile-likelihood fit to the event yields in multiple regions corresponding to positive and negative differences between the pseudorapidities of the charged leptons from top-quark and top-antiquark decays is used to extract the charge asymmetry. At reconstruction level, the asymmetry is found to be $-0.123 \pm 0.136$ (stat.) $\pm \, 0.051$ (syst.). An unfolding procedure is applied to convert the result at reconstruction level into a charge-asymmetry value in a fiducial volume at particle level with the result of $-0.112 \pm 0.170$ (stat.) $\pm \, 0.054$ (syst.). The Standard Model expectations for these two observables are calculated using Monte Carlo simulations with next-to-leading-order plus parton shower precision in quantum chromodynamics and including next-to-leading-order electroweak corrections. They are $-0.084 \, ^{+0.005}_{-0.003}$ (scale) $\pm\, 0.006$ (MC stat.) and $-0.063 \, ^{+0.007}_{-0.004}$ (scale) $\pm\, 0.004$ (MC stat.) respectively, and in agreement with the measurements.
Measured values of the leptonic charge asymmetry ($A_c^{\ell}$) in ttW production in the three lepton channel. Results are given at reconstruction level and at particle level. Expected values are obtained using the Sherpa MC generator.
Definition of the fiducial phase space at particle level with the light lepton candidates $(\ell=e,\mu)$, jets ($j$) and invariant mass of the opposite sign same flavour lepton pair ($m_{OSSF}^{ll}$).
Correlation matrix between the Normalisation Factors and the Nuisance Parameters (NP) in the fit using using both statistical and systematic uncertainties to data in all analysis regions.
Differential cross-section measurements of $Z\gamma$ production in association with hadronic jets are presented, using the full 139 fb$^{-1}$ dataset of $\sqrt{s}=13$ TeV proton-proton collisions collected by the ATLAS detector during Run 2 of the LHC. Distributions are measured using events in which the $Z$ boson decays leptonically and the photon is usually radiated from an initial-state quark. Measurements are made in both one and two observables, including those sensitive to the hard scattering in the event and others which probe additional soft and collinear radiation. Different Standard Model predictions, from both parton-shower Monte Carlo simulation and fixed-order QCD calculations, are compared with the measurements. In general, good agreement is observed between data and predictions from MATRIX and MiNNLO$_\text{PS}$, as well as next-to-leading-order predictions from MadGraph5_aMC@NLO and Sherpa.
Measured differential cross section as a function of observable $ p_{T}^{ll}$. Error on the measured cross-section include all the systematic uncertainties. SM predictions are produced with the event generators at particle level: Sherpa 2.2.4, Sherpa 2.2.11, MadGraph5_aMC@NLO, and MiNNLO$_{PS}$. Fixed order calculations results use MATRIX NNLO. Error represent statistical uncertainty and theoretical uncertainty (PDF and Scale variations).
Measured differential cross section as a function of observable $ p_{T}^{ll}$. Error on the measured cross-section include all the systematic uncertainties. SM predictions are produced with the event generators at particle level: Sherpa 2.2.4, Sherpa 2.2.11, MadGraph5_aMC@NLO, and MiNNLO$_{PS}$. Fixed order calculations results use MATRIX NNLO. Error represent statistical uncertainty and theoretical uncertainty (PDF and Scale variations).
Measured differential cross section as a function of observable $ p_{T}^{ll} - p_{T}^{\gamma}$. Error on the measured cross-section include all the systematic uncertainties. SM predictions are produced with the event generators at particle level: Sherpa 2.2.4, Sherpa 2.2.11, MadGraph5_aMC@NLO, and MiNNLO$_{PS}$. Fixed order calculations results use MATRIX NNLO. Error represent statistical uncertainty and theoretical uncertainty (PDF and Scale variations).
A study of the charge conjugation and parity ($CP$) properties of the interaction between the Higgs boson and $\tau$-leptons is presented. The study is based on a measurement of $CP$-sensitive angular observables defined by the visible decay products of $\tau$-lepton decays, where at least one hadronic decay is required. The analysis uses 139 fb$^{-1}$ of proton$-$proton collision data recorded at a centre-of-mass energy of $\sqrt{s}= 13$ TeV with the ATLAS detector at the Large Hadron Collider. Contributions from $CP$-violating interactions between the Higgs boson and $\tau$-leptons are described by a single mixing angle parameter $\phi_{\tau}$ in the generalised Yukawa interaction. Without assuming the Standard Model hypothesis for the $H\rightarrow\tau\tau$ signal strength, the mixing angle $\phi_{\tau}$ is measured to be $9^{\circ} \pm 16^{\circ}$, with an expected value of $0^{\circ} \pm 28^{\circ}$ at the 68% confidence level. The pure $CP$-odd hypothesis is disfavoured at a level of 3.4 standard deviations. The results are compatible with the predictions for the Higgs boson in the Standard Model.
Observed 1-D likelihood scan of the $CP$-mixing angle $\phi_{\tau}$.
Expected 1-D likelihood scan of the $CP$-mixing angle $\phi_{\tau}$.
Observed 2-D likelihood scan of the signal strength $\mu_{\tau\tau}$ versus the $CP$-mixing angle $\phi_{\tau}$.
A search for pair-produced vector-like quarks using events with exactly one lepton ($e$ or $\mu$), at least four jets including at least one $b$-tagged jet, and large missing transverse momentum is presented. Data from proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb$^{-1}$, are analysed. Vector-like partners $T$ and $B$ of the top and bottom quarks are considered, as is a vector-like $X$ with charge +5/3, assuming their decay into a $W$, $Z$, or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section of $T$ and $B$ quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 TeV assuming mass-degenerate VLQs and branching ratios corresponding to the weak-isospin doublet model, and 1.47 TeV (1.46 TeV) for exclusive $T \rightarrow Zt$ ($B/X \rightarrow Wt$) decays. In addition, lower limits on the $T$ and $B$ quark masses are derived for all possible branching ratios.
Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $T\bar{T}$ and $\mathcal{B}(T\rightarrow Zt) = 100$%.
Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $B\bar{B}$ and $\mathcal{B}(B\rightarrow Wt) = 100$%.
Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $T\bar{T}$ in the singlet model.
The exclusive production of pion pairs in the process $pp\to pp\pi^+\pi^-$ has been measured at $\sqrt{s}$ = 7 TeV with the ATLAS detector at the LHC, using 80 $\mu$b$^{-1}$ of low-luminosity data. The pion pairs were detected in the ATLAS central detector while outgoing protons were measured in the forward ATLAS ALFA detector system. This represents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. A cross-section measurement is performed in two kinematic regions defined by the proton momenta, the pion rapidities and transverse momenta, and the pion-pion invariant mass. Cross section values of $4.8 \pm 1.0 \text{(stat.)} + {}^{+0.3}_{-0.2} \text{(syst.)}\mu$b and $9 \pm 6 \text{(stat.)} + {}^{+2}_{-2}\text{(syst.)}\mu$b are obtained in the two regions; they are compared with theoretical models and provide a demonstration of the feasibility of measurements of this type.
The measured fiducial cross sections. The first systematic uncertainty is the combined systematic uncertainty excluding luminosity, the second is the luminosity
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