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The Quark Gluon Plasma (QGP) produced in ultra relativistic heavy-ion collisions at the Large Hadron Collider (LHC) can be studied by measuring the modifications of jets formed by hard scattered partons which interact with the medium. We studied these modifications via angular correlations of jets with charged hadrons for jets with momenta 20 < $p_{\rm{T}}^{\rm{jet}}$ < 40 GeV/$c$ as a function of the associated particle momentum. The reaction plane fit (RPF) method is used in this analysis to remove the flow modulated background. The analysis of angular correlations for different orientations of the jet relative to the second order event plane allows for the study of the path length dependence of medium modifications to jets. We present the dependence of azimuthal angular correlations of charged hadrons with respect to the angle of the axis of a reconstructed jet relative to the event plane in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. The dependence of particle yields associated with jets on the angle of the jet with respect to the event plane is presented. Correlations at different angles relative to the event plane are compared through ratios and differences of the yield. No dependence of the results on the angle of the jet with respect to the event plane is observed within uncertainties, which is consistent with no significant path length dependence of the medium modifications for this observable.
The near-side and away-side yield vs $p_{T}^{assoc}$ for $20<p_T^{jet}<40$ GeV/$c$ full jets of 30-50% centrality in Pb-Pb collisions. The background uncertainty is non-trivially correlated point-to-point. The correlated systematic uncertainties come from the shape uncertainty of the acceptance correction. There is an additional 5% global scale uncertainty.
The differences between out-of-plane and in-plane yields and mid-plane and in-plane yields on near-side and away-side vs $p_{T}^{assoc}$ for $20<p_T^{jet}<40$ GeV/$c$ full jets of 30-50% centrality in Pb-Pb collisions. The background uncertainty is non-trivially correlated point-to-point. The correlated systematic uncertainties come from the shape uncertainty of the acceptance correction. There is an additional 5% global scale uncertainty.
The ratios of out-of-plane to in-plane yields and mid-plane to in-plane yields on near-side and away-side vs $p_{T}^{assoc}$ for $20<p_T^{jet}<40$ GeV/$c$ full jets of 30-50% centrality in Pb-Pb collisions. The background uncertainty is non-trivially correlated point-to-point. The correlated systematic uncertainties come from the shape uncertainty of the acceptance correction.
Measurements of K∗ (892) 0 and φ(1020)resonance production in Pb–Pb and pp collisions at √ sNN = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (|y| < 0.5) via their hadronic decay channels and the transverse momentum (pT) distributions are obtained for various collision centrality classes up to pT = 20 GeV/c. The pT-integrated yield ratio K∗ (892) 0/K in Pb–Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the φ(1020)/K ratio does not show any suppression. Furthermore, the measured K∗ (892) 0/K ratio in central Pb–Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the φ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K∗ (892) 0 decay products in the hadronic phase of the collisions. The K∗ (892) 0/K yield ratios in Pb–Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4–7 fm/c for central collisions. The pT-differential ratios of K∗ (892) 0/K, φ(1020)/K, K∗ (892) 0/π, φ(1020)/π, p/K ∗ (892) 0 and p/φ(1020) are also presented for Pb–Pb and pp collisions at √ sNN = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-pT phenomenon.
$p_{\rm T}$-distributions of $\rm{K}^{*0}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV.
$p_{\rm T}$-distributions of $\rm{K}^{*0}$ (average of particle and anti-particle) meson measured in pp collisions at $\sqrt{s}$ = 5.02 TeV.
$p_{\rm T}$-distributions of $\phi$ meson measured in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV.
Charged-particle spectra at midrapidity are measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair $\sqrt{s_{\rm NN}}$ = 5.02 TeV and presented in centrality classes ranging from most central (0-5%) to most peripheral (95-100%) collisions. Possible medium effects are quantified using the nuclear modification factor ($R_{\rm AA}$) by comparing the measured spectra with those from proton-proton collisions, scaled by the number of independent nucleon-nucleon collisions obtained from a Glauber model. At large transverse momenta ($8<p_{\rm T}<20$ GeV/$c$), the average $R_{\rm AA}$ is found to increase from about $0.15$ in 0-5% central to a maximum value of about $0.8$ in 75-85% peripheral collisions, beyond which it falls off strongly to below $0.2$ for the most peripheral collisions. Furthermore, $R_{\rm AA}$ initially exhibits a positive slope as a function of $p_{\rm T}$ in the $8$-$20$ GeV/$c$ interval, while for collisions beyond the 80% class the slope is negative. To reduce uncertainties related to event selection and normalization, we also provide the ratio of $R_{\rm AA}$ in adjacent centrality intervals. Our results in peripheral collisions are consistent with a PYTHIA-based model without nuclear modification, demonstrating that biases caused by the event selection and collision geometry can lead to the apparent suppression in peripheral collisions. This explains the unintuitive observation that $R_{\rm AA}$ is below unity in peripheral Pb-Pb, but equal to unity in minimum-bias p-Pb collisions despite similar charged-particle multiplicities.
Nuclear modification factor RAA versus pT for charged particles at midrapidity in 0-5% central Pb-Pb collisions at 5.02 TeV
Nuclear modification factor RAA versus pT for charged particles at midrapidity in 5-10% central Pb-Pb collisions at 5.02 TeV
Nuclear modification factor RAA versus pT for charged particles at midrapidity in 10-15% central Pb-Pb collisions at 5.02 TeV
The measurement of the production of prompt D$^0$, D$^+$, D$^{*+}$, and D$^+_s$ mesons in proton$-$lead (p$-$Pb) collisions at the centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.02 TeV, with an integrated luminosity of $292\pm 11$ $\mu$b$^{-1}$, are reported. Differential production cross sections are measured at mid-rapidity ($-0.96<y_{\rm cms}<0.04$) as a function of transverse momentum ($p_{\rm T}$) in the intervals $0< p_{\rm T} < 36$ GeV/$c$ for D$^0$, $1< p_{\rm T} <36$ GeV/$c$ for D$^+$ and D$^{*+}$, and $2< p_{\rm T} <24$ GeV/$c$ for D$^+_s$ mesons. For each species, the nuclear modification factor $R_{\rm pPb}$ is calculated as a function of $p_{\rm T}$ using a proton-proton (pp) reference measured at the same collision energy. The results are compatible with unity in the whole $p_{\rm T}$ range. The average of the non-strange D mesons $R_{\rm pPb}$ is compared with theoretical model predictions that include initial-state effects and parton transport model predictions. The $p_{\rm T}$ dependence of the D$^0$, D$^+$, and D$^{*+}$ nuclear modification factors is also reported in the interval $1< p_{\rm T} < 36$ GeV/$c$ as a function of the collision centrality, and the central-to-peripheral ratios are computed from the D-meson yields measured in different centrality classes. The results are further compared with charged-particle measurements and a similar trend is observed in all the centrality classes. The ratios of the $p_{\rm T}$-differential cross sections of D$^0$, D$^+$, D$^{*+}$, and D$^+_s$ mesons are also reported. The D$^+_s$ and D$^+$ yields are compared as a function of the charged-particle multiplicity for several $p_{\rm T}$ intervals. No modification in the relative abundances of the four species is observed with respect to pp collisions within the statistical and systematic uncertainties.
Ratio of prompt Ds+ over D+ production cross section as a function of the charged particle pseudorapidity density in p-Pb collisions at $\mathbf{\sqrt{{\textit s}_{\rm NN}}~=~5.02~TeV}$.
Ratio of prompt Ds+ over D+ production cross section as a function of the charged particle pseudorapidity density in p-Pb collisions at $\mathbf{\sqrt{{\textit s}_{\rm NN}}~=~5.02~TeV}$.
$p_{\rm{T}}$ differential cross section of prompt D0 mesons obtained from the analysis without vertexing reconstruction in p-Pb collisions at $\mathbf{\sqrt{{\textit s}_{\rm NN}}~=~5.02~TeV}$.
The measurement of the deuteron and anti-deuteron production in the rapidity range $-1 < y < 0$ as a function of transverse momentum and event multiplicity in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss $\rm{d}E/\rm{d}x$ and via their time-of-flight. Their production in p-Pb collisions is compared to pp and Pb-Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb-Pb collisions at high multiplicities. The mean transverse momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and $\Lambda$ particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p-Pb collisions. In addition, the production of the rare $^{3}{\rm{He}}$ and $^{3}\overline{\rm He}$ nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window $-1 < y < 0$ and the $p_{\rm{T}}$-integrated yield d$N$/d$y$ is extracted. It is found that the yields of protons, deuterons, and $^{3}{\rm{He}}$, normalised by the spin degeneracy factor, follow an exponential decrease with mass number.
Transverse momentum distributions of deuterons in the 0-10% V0A multiplicity class
Transverse momentum distributions of anti-deuterons in the 60-100% V0A multiplicity class
$\bar{d}$/d ratio as a function of transverse momentum in the 0-10% V0A multiplicity class
We present a study of the inclusive charged-particle transverse momentum ( $p_{\mathrm{T}}$ ) spectra as a function of charged-particle multiplicity density at mid-pseudorapidity, $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta $ , in pp collisions at $\sqrt{s}=5.02$ and 13 TeV covering the kinematic range $|\eta |<0.8$ and $0.15<p_{\mathrm{T}} <20$ GeV/c. The results are presented for events with at least one charged particle in $|\eta |<1$ (INEL $\,>0$ ). The $p_\mathrm{T}$ spectra are reported for two multiplicity estimators covering different pseudorapidity regions. The $p_{\mathrm{T}}$ spectra normalized to that for INEL $\,>0$ show little energy dependence. Moreover, the high- $p_{\mathrm{T}}$ yields of charged particles increase faster than the charged-particle multiplicity density. The average ${ p}_{\mathrm{T}}$ as a function of multiplicity and transverse spherocity is reported for pp collisions at $\sqrt{s}=13$ TeV. For low- (high-) spherocity events, corresponding to jet-like (isotropic) events, the average $p_\mathrm{T}$ is higher (smaller) than that measured in INEL $\,>0$ pp collisions. Within uncertainties, the functional form of $\langle p_{\mathrm{T}} \rangle (N_{\mathrm{ch}})$ is not affected by the spherocity selection. While EPOS LHC gives a good description of many features of data, PYTHIA overestimates the average $p_{\mathrm{T}}$ in jet-like events.
Transverse momentum spectra as a function of the event multiplicity for pp collisions at 13 TeV. Event multiplicity is estimated with the number of SPD tracklets. Uncorrelated systematic uncertainties are the multiplicity dependent systematic uncertainties.
Transverse momentum spectra as a function of the event multiplicity for pp collisions at 5.02 TeV. Event multiplicity is estimated with the number of SPD tracklets. Uncorrelated systematic uncertainties are the multiplicity dependent systematic uncertainties.
Transverse momentum spectra as a function of the event multiplicity for pp collisions at 13 TeV. Event multiplicity is estimated with the signal in the VZERO detector. Uncorrelated systematic uncertainties are the multiplicity dependent systematic uncertainties.
The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at a centre-of-momentum energy of $\sqrt{s}=$ 7 TeV. The measurement is performed with the electromagnetic calorimeter EMCal and the central tracking detectors, covering a range of $|\eta|<0.27$ in pseudorapidity and a transverse momentum range of $ 10 < p_{\rm T}^{\gamma} < $ 60 GeV/$c$. The result extends the $p_{\rm T}$ coverage of previously published results of the ATLAS and CMS experiments at the same collision energy to smaller $p_{\rm T}$. The measurement is compared to next-to-leading order perturbative QCD calculations and to the results from the ATLAS and CMS experiments. All measurements and theory predictions are in agreement with each other.
Double $p_{T}$-differential production cross section of isolated photons in pp collisions at $\sqrt{s}$=7 TeV in the rapidity interval -0.27<$\eta$<0.27.
The cross section of jets reconstructed from charged particles is measured in the transverse momentum range of $5<p_\mathrm{T}<100\ \mathrm{GeV}/c$ in pp collisions at the center-of-mass energy of $\sqrt{s} = 5.02\ \mathrm{TeV}$ with the ALICE detector. The jets are reconstructed using the anti-$k_\mathrm{T}$ algorithm with resolution parameters $R=0.2$, $0.3$, $0.4$, and $0.6$ in the pseudorapidity range $|\eta|< 0.9-R$. The charged jet cross sections are compared with the leading order (LO) and to next-to-leading order (NLO) perturbative Quantum ChromoDynamics (pQCD) calculations. It was found that the NLO calculations agree better with the measurements. The cross section ratios for different resolution parameters were also measured. These ratios increase from low $p_\mathrm{T}$ to high $p_\mathrm{T}$ and saturate at high $p_\mathrm{T}$, indicating that jet collimation is larger at high $p_\mathrm{T}$ than at low $p_\mathrm{T}$. These results provide a precision test of pQCD predictions and serve as a baseline for the measurement in Pb$-$Pb collisions at the same energy to quantify the effects of the hot and dense medium created in heavy-ion collisions at the LHC.
Charged jet differential cross sections without UE subtraction in pp collisions at $\sqrt{s}$ = 5.02 TeV with the leading track bias. All jets must contain at least one track with $p_{T}$ > 5 GeV/$c$. Statistical uncertainties are displayed as vertical error bars. The total systematic uncertainties are shown as shaded bands around the data points. Data are scaled to enhance visibility
Fig. 6: Charged jet cross section ratios for $\\sigma$(R = 0.2)/$\\sigma$(R = 0.4) (Red) and $\\sigma$(R = 0.2)/$\\sigma$(R = 0.6). The systematic uncertainty of the cross section ratio is indicated by a shaded band drawn around data points.
Fig. 3: Fully corrected charged jet differential cross sections in pp collisions at $\\sqrt{s}$ = 5.02 TeV. Statistical uncertainties are displayed as vertical error bars. The total systematic uncertainties are shown as shaded bands around the data points. Data are scaled to enhance visibility.
The coherent photoproduction of J/$\psi$ was measured in ultra-peripheral Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\rm{NN}}}=5.02$ TeV with the ALICE detector. The J/$\psi$ is detected via its dimuon decay in the forward rapidity region for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 $\mu$b$^{-1}$. The cross section for coherent J/$\psi$ production is presented in six rapidity bins, covering the interval $-4.0 < y < -2.5$. The results are compared with theoretical models for coherent J/$\psi$ photoproduction. The results indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of $\psi'$ to J/$\psi$ coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons.
Differential cross section as a function of rapidity for coherent J/PSI photoproduction in ultra-peripheral Pb-Pb collisions.
Production cross sections of muons from semi-leptonic decays of charm and beauty hadrons were measured at forward rapidity ($2.5<y<4$) in proton--proton (pp) collisions at a centre-of-mass energy $\sqrt{s}=5.02$ TeV with the ALICE detector at the CERN LHC. The results were obtained in an extended transverse momentum interval, $2 < p_{\rm T} < 20$ GeV/$c$, and with an improved precision compared to previous measurements performed in the same rapidity interval at centre-of-mass energies $\sqrt{s}= 2.76$ and 7 TeV. The $p_{\rm T}$- and $y$-differential production cross sections as well as the $p_{\rm T}$-differential production cross section ratios between different centre-of-mass energies and different rapidity intervals are described, within experimental and theoretical uncertainties, by predictions based on perturbative QCD.
$p_{\rm T}$-differential production cross section of muons from heavy-flavour hadron decays at forward rapidity in pp collisions at $\sqrt{s}=5.02$ TeV in the rapidity interval $2.5 < y < 4$.
Production cross section of muons from heavy-flavour hadron decays as a function of rapidity in pp collisions at $\sqrt{s} = 5.02$ TeV for the $p_{\rm T}$ interval $2 < p_{\rm T} < 7$ GeV/$c$.
Production cross section of muons from heavy-flavour hadron decays as a function of rapidity in pp collisions at $\sqrt{s} = 5.02$ TeV for the $p_{\rm T}$ interval $7 < p_{\rm T} < 20$ GeV/$c$.
Inclusive $\Upsilon$(1S) and $\Upsilon$(2S) production have been measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair $\sqrt{s_{_{\rm NN}}}=5.02$ TeV, using the ALICE detector at the CERN LHC. The $\Upsilon$ mesons are reconstructed in the centre-of-mass rapidity interval $2.5<y<4$ and in the transverse-momentum range $p_{\rm T}<15$ GeV/$c$, via their decays to muon pairs. In this Letter, we present results on the inclusive $\Upsilon$(1S) nuclear modification factor $R_{\rm AA}$ as a function of collision centrality, transverse momentum and rapidity. The $\Upsilon$(1S) and $\Upsilon$(2S) $R_{\rm AA}$, integrated over the centrality range 0-90%, are $0.37 \pm 0.02 {\rm{(stat)}}\pm 0.03 {\rm{(syst)}}$ and $0.10 \pm 0.04 {\rm{(stat)}}\pm 0.02 {\rm{(syst)}}$, respectively, leading to a ratio $R_{\rm{AA}}^{\Upsilon(\rm2S)}/R_{\rm{AA}}^{\Upsilon(\rm1S)}$ of $0.28\pm0.12\text{(stat)}\pm0.06\text{(syst)}$. The observed $\Upsilon$(1S) suppression increases with the centrality of the collision and no significant variation is observed as a function of transverse momentum and rapidity.
Inclusive $\Upsilon$(1S) $R_{\rm AA}$ and Pb-Pb yields for the centrality, transverse-momentum and rapidity ranges 0-90%, $0<p_{\rm T}<15$ GeV/$c$ and $2.5<y<4$, respectively. Statistical and systematic uncertainties are reported. (The yield is not normalized to the kinematic intervals).
Inclusive $\Upsilon$(1S) $R_{\rm AA}$ and Pb-Pb yields as a function of collision centrality. The transverse-momentum and rapidity ranges are $0<p_{\rm T}<15$ GeV/$c$ and $2.5<y<4$, respectively. Statistical and systematic uncertainties are reported. A global systematic uncertainty of 7.7% (4.9%) affects all the $R_{\rm AA}$ (yield) values. (The yields are not normalized to the kinematic intervals).
Inclusive $\Upsilon$(1S) $R_{\rm AA}$ and Pb-Pb yields as a function of transverse momentum. The centrality and rapidity ranges are 0-90% and $2.5<y<4$, respectively. Statistical and systematic uncertainties are reported. A global systematic uncertainty of 2.7% (2.3%) affects all the $R_{\rm AA}$ (yield) values.
Inclusive J/$\psi$ production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity ($|y| < 0.9$) in the dielectron decay channel down to zero transverse momentum $p_{\rm T}$, using a data sample corresponding to an integrated luminosity of $L_{\rm int} = 19.4 \pm$ 0.4 nb$^{-1}$. The measured $p_{\rm T}$-integrated inclusive J/$\psi$ production cross section is d$\sigma$/d$y$ = 5.64 $\pm$ 0.22 (stat.) $\pm 0.33$ (syst.) $\pm 0.12$ (lumi.) $\mu$b. The $p_{\rm T}$-differential cross section d$^{2} \sigma$/d$p_{\rm T}$d$y$ is measured in the $p_{\rm T}$ range 0$-$10 GeV/$c$ and compared with state-of-the-art perturbative QCD calculations. The J/$\psi$ $\langle p_{\rm T} \rangle$ and $\langle p_{\rm T}^{2} \rangle$ are extracted and compared with results obtained at other collision energies.
$p_{\rm T}$-integrated inclusive J/$\psi$ cross section.
$p_{\rm T}$-differential inclusive J/$\psi$ cross section.
Mean $p_{\rm T}$ square of the inclusive J/$\psi$ spectrum at 5.02 TeV.
The first measurement of the $\Upsilon(1{\rm S})$ elliptic flow coefficient ($v_2$) is performed at forward rapidity (2.5 $<$ $y$ $<$ 4) in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector at the LHC. The results are obtained with the scalar product method and are reported as a function of transverse momentum ($p_{\rm{T}}$) up to 15 GeV/$c$ in the 5-60% centrality interval. The measured $\Upsilon(1{\rm S})$ $v_2$ is consistent with zero and with the small positive values predicted by transport models within uncertainties. The $v_2$ coefficient in 2 $<$ $p_{\rm T}$ $<$ 15 GeV/$c$ is lower than that of inclusive J/$\psi$ mesons in the same $p_{\rm{T}}$ interval by 2.6 standard deviations. These results, combined with earlier suppression measurements, are in agreement with a scenario in which the $\Upsilon$(1S) production in Pb-Pb collisions at LHC energies is dominated by dissociation limited to the early stage of the collision whereas in the J/$\psi$ case there is substantial experimental evidence of an additional regeneration component.
The J/$\psi$ $v_2$ coefficient as a function of $p_{\rm T}$ in 5-60% centrality interval in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
The $\Upsilon$(1S) $v_2$ coefficient as a function of $p_{\rm T}$ in 5-60% centrality interval in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
The J/$\psi$ $v_2$ coefficient in three centrality intervals integrated over the transverse momentum range 2~$<$~$p_{\rm T}$~$<$~15 GeV/$c$ in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
Two-particle correlations in high-energy collision experiments enable the extraction of particle source radii by using the Bose-Einstein enhancement of pion production at low relative momentum $q\propto 1/R$. It was previously observed that in $\rm{p}\rm{p}$ collisions at $\sqrt{s}=7$ TeV the average pair transverse momentum $k_{\rm T}$ range of such analyses is limited due to large background correlations which were attributed to mini-jet phenomena. To investigate this further, an event-shape dependent analysis of Bose-Einstein correlations for pion pairs is performed in this work. By categorizing the events by their transverse sphericity $S_{\rm T}$ into spherical $(S_\textrm{T}>0.7)$ and jet-like $(S_\textrm{T}<0.3)$ events a method was developed that allows for the determination of source radii for much larger values of $k_{\rm T}$ for the first time. Spherical events demonstrate little or no background correlations while jet-like events are dominated by them. This observation agrees with the hypothesis of a mini-jet origin of the non-femtoscopic background correlations and gives new insight into the physics interpretation of the $k_{\rm T}$ dependence of the radii. The emission source size in spherical events shows a substantially diminished $k_{\rm T}$ dependence, while jet-like events show indications of a negative trend with respect to $k_{\rm T}$ in the highest multiplicity events. Regarding the emission source shape, the correlation functions for both event sphericity classes show good agreement with an exponential shape, rather than a Gaussian one.
Opposite-sign pion pair correlation functions in data for sphericity S_{T} < 0.3 (jet-like events).
Opposite-sign pion pair correlation functions in PYTHIA simulations for sphericity S_{T} < 0.3 (jet-like events).
Opposite-sign pion pair correlation functions in data for sphericity S_{T} > 0.7 (spherical events).
An improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = $ 5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the d$N$/d($ct$) spectrum. The measured value, $\tau$ = 242$^{+34}_{-38}$ (stat.) $\pm$ 17 (syst.) ps, is compatible with all the available theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle.
(Hypertriton + Anti-Hypertriton)dN/d(ct) distribution.
This work presents the first experimental observation of the attractive strong interaction between a proton and a multi-strange baryon (hyperon) $\Xi^-$. The result is extracted from two-particle correlations of combined $\rm{p}-\Xi^{-}$$\oplus$$\rm{\overline{p}}-\overline{\Xi}^{+}$ pairs measured in p-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV at the LHC with ALICE. The measured correlation function is compared with the prediction obtained assuming only an attractive Coulomb interaction and a standard deviation in the range $[3.6,5.3]$ is found. Since the measured $\rm{p}-\Xi^{-}$$\oplus$$\rm{\overline{p}}-\overline{\Xi}^{+}$ correlation is significantly enhanced with respect to the Coulomb prediction, the presence of an additional, strong, attractive interaction is evident. The data are compatible with recent lattice calculations by the HAL-QCD Collaboration, with a standard deviation in the range $ [1.8,3.7]$. The lattice potential predicts a shallow repulsive $\Xi^-$ interaction within pure neutron matter at saturation densities and this implies stiffer equations of state for neutron-rich matter including hyperons. Implications of the strong interaction for the modeling of neutron stars are discussed.
The p$-$p $\oplus$ $\overline{\mathrm{p}}-\overline{\mathrm{p}}$ correlation function.
The p$-\Xi^{-}$ $\oplus$ $\overline{\mathrm{p}}-\overline{\Xi}^{-}$ correlation function.
Measurements of anisotropic flow coefficients ($v_n$) and their cross-correlations using two- and multi-particle cumulant methods are reported in collisions of pp at $\sqrt{s} = 13$ TeV, p-Pb at $\sqrt{s_{_{\rm NN}}} = 5.02$ TeV, Xe-Xe at $\sqrt{s_{_{\rm NN}}} = 5.44$ TeV, and Pb-Pb at $\sqrt{s_{_{\rm NN}}} = 5.02$ TeV recorded with the ALICE detector. These measurements are performed as a function of multiplicity in the mid-rapidity region $|\eta|<0.8$ for the transverse momentum range $0.2 < p_{\rm T} < 3.0$ GeV/$c$. An ordering of the coefficients $v_2 > v_3 > v_4$ is found in pp and p-Pb collisions, similar to that seen in large collision systems, while a weak $v_2$ multiplicity dependence is observed relative to nucleus--nucleus collisions in the same multiplicity range. Using the novel subevent method, $v_{2}$ measured in pp and p-Pb collisions with four-particle cumulants is found to be compatible with that from six-particle cumulants. The symmetric cumulants $SC(m,n)$ calculated with the subevent method which evaluate the correlation strength between $v_n^2$ and $v_m^2$ are also presented. The presented data, which add further support to the existence of long-range multi-particle azimuthal correlations in high multiplicity pp and p-Pb collisions, can neither be described by PYTHIA8 nor by IP-Glasma+MUSIC+UrQMD model calculations, and hence provide new insights into the understanding of collective effects in small collision systems.
$v_2\{2\}$ with $|\Delta \eta| > 1.4$ in pp collisions at $\sqrt{s} = 13$ TeV.
$v_3\{2\}$ with $|\Delta \eta| > 1.0$ in pp collisions at $\sqrt{s} = 13$ TeV.
$v_4\{2\}$ with $|\Delta \eta| > 1.0$ in pp collisions at $\sqrt{s} = 13$ TeV.
In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, $\rm{d}N_{\rm{ch}}/\rm{d}\eta$, and total charged-particle multiplicity, $N_{\rm{ch}}^{\rm{tot}}$, in Xe-Xe collisions at a centre-of-mass energy per nucleon--nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.44 TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of $-3.5 < \eta < 5$. The values of $\rm{d}N_{\rm{ch}}/\rm{d}\eta$ at mid-rapidity and $N_{\rm{ch}}^{\rm{tot}}$ for central collisions, normalised to the number of nucleons participating in the collision ($N_{\rm{part}}$) as a function of $\sqrt{s_{\rm NN}}$, follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of $N_{\rm{part}}$, and up to the 10% most central collisions the trends are the same as the ones observed in Pb-Pb at a similar energy. For more central collisions, the Xe-Xe scaled multiplicities exceed those in Pb-Pb for a similar $N_{\rm{part}}$. The results are compared to phenomenological models and theoretical calculations based on different mechanisms for particle production in nuclear collisions. All considered models describe the data reasonably well within 20%.
Values of $2/\langle N_\mathrm{part} \rangle \langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle$ and $2/\langle N_\mathrm{part} \rangle N^\mathrm{tot}_\mathrm{ch}$ in Xe--Xe collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44\,\mathrm{TeV}$ for the top 5$\%$ central collisions.
Values of $2/\langle N_\mathrm{part} \rangle \langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle$ and $2/\langle N_\mathrm{part} \rangle N^\mathrm{tot}_\mathrm{ch}$ as a function of $\langle N_\mathrm{part} \rangle$ in Xe--Xe collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44\,\mathrm{TeV}$.
Values of $2/\langle N_\mathrm{part} \rangle \langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle$ and $2/\langle N_\mathrm{part} \rangle N^\mathrm{tot}_\mathrm{ch}$ as a function of $\langle N_\mathrm{part} \rangle$ in Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.02\,\mathrm{TeV}$.
This work presents new constraints on the existence and the binding energy of a possible $\Lambda$-$\Lambda$ bound state, the H-dibaryon, derived from $\Lambda$-$\Lambda$ femtoscopic measurements by the ALICE collaboration. The results are obtained from a new measurement using the femtoscopy technique in pp collisions at $\sqrt{s}=13$ TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, combined with previously published results from p-Pb collisions at $\sqrt{s}=7$ TeV. The $\Lambda$-$\Lambda$ scattering parameter space, spanned by the inverse scattering length $f_0^{-1}$ and the effective range $d_0$, is constrained by comparing the measured $\Lambda$-$\Lambda$ correlation function with calculations obtained within the Lednicky model. The data are compatible with hypernuclei results and lattice computations, both predicting a shallow attractive interaction, and permit to test different theoretical approaches describing the $\Lambda$-$\Lambda$ interaction. The region in the $(f_0^{-1},d_0)$ plane which would accommodate a $\Lambda$-$\Lambda$ bound state is substantially restricted compared to previous studies. The binding energy of the possible $\Lambda$-$\Lambda$ bound state is estimated within an effective-range expansion approach and is found to be $B_{\Lambda\Lambda}=3.2^{+1.6}_{-2.4}\mathrm{(stat)}^{+1.8}_{-1.0}\mathrm{(syst)}$ MeV.
Exclusion plot for the $\Lambda$-$\Lambda$ binding energy (statistical uncertainty).
Exclusion plot for the $\Lambda$-$\Lambda$ binding energy (total uncertainty).
p-p correlation function in p-p collisions at $\sqrt{s}=13$ TeV.
The production of charm jets in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=7$ TeV was measured with the ALICE detector at the CERN Large Hadron Collider. The measurement is based on a data sample corresponding to a total integrated luminosity of $6.23$ ${\rm nb}^{-1}$, collected using a minimum-bias trigger. Charm jets are identified by the presence of a D$^0$ meson among their constituents. The D$^0$ mesons are reconstructed from their hadronic decay D$^0\rightarrow$K$^{-}\pi^{+}$. The D$^0$-meson tagged jets are reconstructed using tracks of charged particles (track-based jets) with the anti-$k_{\mathrm{T}}$ algorithm in the jet transverse momentum range $5<p_{\rm{T,jet}}^{\mathrm{ch}}<30$ ${\rm GeV/}c$ and pseudorapidity $|\eta_{\rm jet}|<0.5$. The fraction of charged jets containing a D$^0$-meson increases with $p_{\rm{T,jet}}^{\rm{ch}}$ from $0.042 \pm 0.004\, \mathrm{(stat)} \pm 0.006\, \mathrm{(syst)}$ to $0.080 \pm 0.009\, \rm{(stat)} \pm 0.008\, \rm{(syst)}$. The distribution of D$^0$-meson tagged jets as a function of the jet momentum fraction carried by the D$^0$ meson in the direction of the jet axis ($z_{||}^{\mathrm{ch}}$) is reported for two ranges of jet transverse momenta, $5<p_{\rm{T,jet}}^{\rm{ch}}<15$ ${\rm GeV/}c$ and $15<p_{\rm{T,jet}}^{\rm{ch}}<30$ ${\rm GeV/}c$ in the intervals $0.2<z_{||}^{\rm{ch}}<1.0$ and $0.4<z_{||}^{\rm{ch}}<1.0$, respectively. The data are compared with results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and with a Next-to-Leading-Order perturbative Quantum Chromodynamics calculation, obtained with the POWHEG method and interfaced with PYTHIA 6 for the generation of the parton shower, fragmentation, hadronisation and underlying event.
Ratio of the $p_{\rm T}$-differential cross section of charm jets tagged with D$^0$ mesons to the inclusive jet cross section in pp collisions at $\sqrt{s}$ = 7 TeV.
$p_{\rm T}$-differential cross section of charm jets tagged with D$^0$ mesons in pp collisions at $\sqrt{s}$ = 7 TeV.
$z_{||}^{\rm ch}$-differential cross section of D$^0$-meson tagged track-based jets in pp collisions at $\sqrt{s}$ = 7 TeV, with $p_{\rm T,D}$ > 2 GeV/$c$ and 5 < $p_{\rm T,jet}^{\rm ch}$ < 15 GeV/$c$.
The correlations of identical charged kaons were measured in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV by the ALICE experiment at the LHC. The femtoscopic invariant radii and correlation strengths were extracted from one-dimensional kaon correlation functions and were compared with those obtained in pp and Pb-Pb collisions at $\sqrt{s}=7$ TeV and $\sqrt{s_{\rm NN}}=2.76$ TeV, respectively. The presented results also complement the identical-pion femtoscopic data published by the ALICE collaboration. The extracted radii increase with increasing charged-particle multiplicity and decrease with increasing pair transverse momentum. At comparable multiplicities, the radii measured in p-Pb collisions are found to be close to those observed in pp collisions. The obtained femtoscopic parameters are reproduced by the EPOS hadronic interaction model and disfavor models with large initial size or strong collective expansion at low multiplicities.
Correlation function as a function of pair relative momentum for 0-20% multiplicity class and pair transverse momentum range (0.2-0.5) GeV/c.
Correlation function as a function of pair relative momentum for 0-20% multiplicity class and pair transverse momentum range (0.5-1.0) GeV/c.
Correlation function as a function of pair relative momentum for 20-40% multiplicity class and pair transverse momentum range (0.2-0.5) GeV/c.
We report on the first femtoscopic measurement of baryon pairs, such as p-p, p-$\Lambda$ and $\Lambda$-$\Lambda$, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at $\sqrt{s}$ = 7 TeV. This study demonstrates the feasibility of such measurements in pp collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented. The p-p, p-$\Lambda$ and $\Lambda$-$\Lambda$ correlation functions were fitted simultaneously with the help of a new tool developed specifically for the femtoscopy analysis in small colliding systems 'Correlation Analysis Tool using the Schr\"odinger Equation' (CATS). Within the assumption that in pp collisions the three particle pairs originate from a common source, its radius is found to be equal to $r_{0} = 1.144\pm0.019$ (stat) $^{+0.069}_{-0.012}$ (syst) fm. The sensitivity of the measured p-$\Lambda$ correlation is tested against different scattering parameters which are defined by the interaction among the two particles, but the statistics is not sufficient yet to discriminate among different models. The measurement of the $\Lambda$-$\Lambda$ correlation function constrains the phase space spanned by the effective range and scattering length of the strong interaction. Discrepancies between the measured scattering parameters and the resulting correlation functions at LHC and RHIC energies are discussed in the context of various models.
The p$-$p $\oplus$ $\overline{\mathrm{p}}-\overline{\mathrm{p}}$ correlation function.
The p$-\Lambda$ $\oplus$ $\overline{\mathrm{p}}-\overline{\Lambda}$ correlation function.
The $\Lambda-\Lambda$ $\oplus$ $\overline{\Lambda}-\overline{\Lambda}$ correlation function.
The second and the third order anisotropic flow, V2 and V3 , are mostly determined by the corresponding initial spatial anisotropy coefficients, ε2 and ε3 , in the initial density distribution. In addition to their dependence on the same order initial anisotropy coefficient, higher order anisotropic flow, Vn ( n>3 ), can also have a significant contribution from lower order initial anisotropy coefficients, which leads to mode-coupling effects. In this Letter we investigate the linear and non-linear modes in higher order anisotropic flow Vn for n=4 , 5, 6 with the ALICE detector at the Large Hadron Collider. The measurements are done for particles in the pseudorapidity range |η|<0.8 and the transverse momentum range 0.2<pT<5.0 GeV/c as a function of collision centrality. The results are compared with theoretical calculations and provide important constraints on the initial conditions, including initial spatial geometry and its fluctuations, as well as the ratio of the shear viscosity to entropy density of the produced system.
Study of relationship between linear and non-linear modes in higher order anisotropic flow in Pb–Pb collisions at 2.76 TeV.
Study of relationship between linear and non-linear modes in higher order anisotropic flow in Pb–Pb collisions at 2.76 TeV.
Study of relationship between linear and non-linear modes in higher order anisotropic flow in Pb–Pb collisions at 2.76 TeV.
A measurement of the production of prompt $\Lambda_{\rm c}^{+}$ baryons in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02 $ TeV with the ALICE detector at the LHC is reported. The $\Lambda_{\rm c}^{+}$ and $\overline{\Lambda}_{\rm c}^{-}$ were reconstructed at midrapidity ($|y| < 0.5$) via the hadronic decay channel $\Lambda_{\rm c}^{+}\rightarrow {\rm p} {\rm K}_{\rm S}^{0}$ (and charge conjugate) in the transverse momentum and centrality intervals $6 < p_{\rm T} <12$ GeV/$c$ and 0-80%. The $\Lambda_{\rm c}^{+}$/D$^0$ ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02 $ TeV. In particular, the values in p-Pb and Pb-Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties. The $\Lambda_{\rm c}^{+}$/D$^0$ ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The $\Lambda_{\rm c}^{+}$ nuclear modification factor, $R_{\rm AA}$, is also presented. The measured values of the $R_{\rm AA}$ of $\Lambda_{\rm c}^{+}$, D$_{\rm s}^+$ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy $(R_{\rm AA}^{{\rm D}^{0}}<R_{\rm AA}^{{\rm D}_{\rm s}^+}<R_{\rm AA}^{\Lambda_{\rm c}^{+}})$, conceivable with a contribution of recombination mechanisms to charm hadron formation in the medium.
$\Lambda_{\rm {c}}^{+}$/${\rm D}^{0}$ ratio in 0-80% most central Pb-Pb collisions at $\sqrt{s_{\rm {NN}}} = 5.02$ TeV in the transverse momentum interval 6 < $p_{\rm {T}}$ < 12 GeV/${\it {c}}$
The nuclear modification factor $R_\mathrm{AA}$ of prompt $\Lambda_{\rm {c}}^{+}$ baryons in 0-80% most central Pb-Pb collisions at $\sqrt{s_{\rm {NN}}} = 5.02$ TeV in the transverse momentum interval 6 < $p_{\rm {T}}$ < 12 GeV/${\it {c}}$
The transverse structure of jets was studied via jet fragmentation transverse momentum ($j_{\rm{T}}$) distributions, obtained using two-particle correlations in proton-proton and proton-lead collisions, measured with the ALICE experiment at the LHC. The highest transverse momentum particle in each event is used as the trigger particle and the region $3 < p_{\rm{Tt}} < 15$ GeV/$c$ is explored in this study. The measured distributions show a clear narrow Gaussian component and a wide non-Gaussian one. Based on Pythia simulations, the narrow component can be related to non-perturbative hadronization and the wide component to quantum chromodynamical splitting. The width of the narrow component shows a weak dependence on the transverse momentum of the trigger particle, in agreement with the expectation of universality of the hadronization process. On the other hand, the width of the wide component shows a rising trend suggesting increased branching for higher transverse momentum. The results obtained in pp collisions at $\sqrt{s}$ = 7 TeV and in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV are compatible within uncertainties and hence no significant cold nuclear matter effects are observed. The results are compared to previous measurements from CCOR and PHENIX as well as to Pythia 8 and Herwig 7 simulations.
trigger particle momentum dependence of observables RMS for narrow component in p-p collisions at 7 TeV with 0.2<xlong<0.4.
trigger particle momentum dependence of observables RMS for narrow component in p-p collisions at 7 TeV with 0.4<xlong<0.6.
trigger particle momentum dependence of observables RMS for narrow component in p-p collisions at 7 TeV with 0.6<xlong<1.0.
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