Partonic collectivity is one of the necessary signatures for the formation of Quark-Gluon-Plasma in high-energy nuclear collisions. Number of Constituent Quarks (NCQ) scaling has been observed for light hadron elliptic flow $v_2$ in top energy nuclear collisions at RHIC and the LHC, and this has been theoretically suggested as strong evidence for partonic collectivity. In this letter, a systematic analysis of $v_2$ of $\pi^{\pm}$, $K^{\pm}$, $K^{0}_{S}$, $p$ and $\Lambda$ in Au+Au collisions at ${\sqrt{s_{_{\rm{NN}}}}}$ = 3.2, 3.5, 3.9, and 4.5 GeV, with the STAR experiment at RHIC, is presented. NCQ scaling is markedly violated at 3.2 GeV, consistent with a hadronic-interaction dominated equation of state. However, as the collision energy increases, a gradual evolution to NCQ scaling is observed. This beam-energy dependence of $v_2$ for all hadrons studied provides evidence for the onset of dominant partonic interactions by ${\sqrt{s_{_{\rm{NN}}}}}$ = 4.5 GeV.
$p_{T}$ dependence of $v_{2}$ for $\pi^{+}$ in Au+Au collisions at 3 GeV
$p_{T}$ dependence of $v_{2}$ for $\pi^{+}$ in Au+Au collisions at 3.2 GeV
$p_{T}$ dependence of $v_{2}$ for $\pi^{+}$ in Au+Au collisions at 3.5 GeV
This paper presents a study of the inclusive forward J/$\psi$ yield as a function of forward charged-particle multiplicity in pp collisions at $\sqrt{s} = 13$ TeV using data collected by the ALICE experiment at the CERN LHC. The results are presented in terms of relative J/$\psi$ yields and relative charged-particle multiplicities with respect to these quantities obtained in inelastic collisions having at least one charged particle in the pseudorapidity range $|\eta| < 1$. The J/$\psi$ mesons are reconstructed via their decay into $\mu^+ \mu^-$ pairs in the forward rapidity region ($2.5 < y < 4$). The relative multiplicity is estimated in the forward pseudorapidity range $-3.7 < \eta < -1.7$, which overlaps with the J/$\psi$ rapidity region. The results show a steeper-than-linear increase of the J/$\psi$ yields versus the multiplicity. They are compared with previous measurements and theoretical model calculations.
Forward inclusive J/$\psi$ relative yield as a function of the relative multiplicity in −3.7 < $\eta$ < −1.7 in INEL > 0 pp collisions at $\sqrt{s}$ = 13 TeV.
A measurement of the WZ$γ$ triboson production cross section is presented. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis focuses on the final state with three charged leptons, $\ell^\pmν\ell^+\ell^-$, where $\ell$ = e or $μ$, accompanied by an additional photon. The observed (expected) significance of the WZ$γ$ signal is 5.4 (3.8) standard deviations. The cross section is measured in a fiducial region, where events with an $\ell$ originating from a tau lepton decay are excluded, to be 5.48 $\pm$ 1.11 fb, which is compatible with the prediction of 3.69 $\pm$ 0.24 fb at next-to-leading order in quantum chromodynamics. Exclusion limits are set on anomalous quartic gauge couplings and on the production cross sections of massive axion-like particles.
The distributions of the variables used in the simultaneous fit for the nonprompt $l$ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
The distributions of the variables used in the simultaneous fit for the nonprompt $\gamma$ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
The distributions of the variables used in the simultaneous fit for the ZZ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
Correlations among conserved quantum numbers, such as the net-electric charge, the net-baryon, and the net-strangeness in heavy-ion collisions, are crucial for exploring the QCD phase diagram. In this letter, these correlations are investigated using net-proton number (as a proxy for the net-baryon), net-kaon number (for the net-strangeness), and net-charged particle number in Pb-Pb collisions at $\sqrt{s_\text{NN}}=5.02$ TeV with the ALICE detector. The observed correlations deviate from the Poissonian baseline, with a more pronounced deviation at LHC energies than at RHIC. Theoretical calculations of the Thermal-FIST hadron resonance gas model, HIJING, and EPOS LHC event generators are compared with experimental results, where a significant impact of resonance decays is observed. Thermal-FIST calculations under the grand canonical and canonical ensembles highlight significant differences, underscoring the role of local charge conservation in explaining the data. Recent lattice QCD studies have demonstrated that the magnetic field generated by spectator protons in heavy-ion collisions affects susceptibility ratios, in particular those related to the net-electric charge and the net-baryon numbers. The experimental findings are in qualitative agreement with the expectations of lattice QCD.
$\kappa^{2}_{\pi}$ as a function of centrality (%) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV for Set 1 $p_\mathrm{T}$ acceptance.
$\kappa^{2}_{\pi}$ as a function of centrality (%) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV for Set 2 $p_\mathrm{T}$ acceptance.
$\kappa^{2}_\mathrm{K}$ as a function of centrality (%) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV for Set 1 $p_\mathrm{T}$ acceptance.
A search is performed for long-lived heavy neutral leptons (HNLs), produced through the decay of a $W$ boson along with a muon or electron. Two channels are explored: a leptonic channel, in which the HNL decays into two leptons and a neutrino, and a semi-leptonic channel, in which the HNL decays into a lepton and a charged pion. The search is performed with 140~fb$^{-1}$ of $\sqrt{s} = 13$ TeV proton--proton collision data collected by ATLAS during Run 2 of the Large Hadron Collider. No excess of events is observed; Dirac-like and Majorana-like HNLs with masses below 14.5 GeV and mixing coefficients as small as 10$^{-7}$ are excluded at the 95% confidence level. The results are interpreted under different assumptions on the flavour of the leptons from the HNL decays.
The DV reconstruction efficiency for an HNL with $m_N = 2$ GeV and $c\tau_N = 10$ mm, as a function of the DV radius $r_{DV}$ using the customised vertex reconstruction for a selection of the fully leptonic MC samples. Different flavour combinations are shown.
The DV reconstruction efficiency for an HNL with $m_N = 2$ GeV and $c\tau_N = 10$ mm, as a function of the DV radius $r_{DV}$ using the customised vertex reconstruction for a selection of the semi-leptonic MC samples. Different flavour combinations are shown.
The DV reconstruction efficiency for an HNL with $m_N = 2$ GeV and $c\tau_N = 10$ mm, as a function of the DV radius $r_{DV}$ using the customised vertex reconstruction for a selection of the fully leptonic MC samples. Decays from HNLs are shown for $\mu\mu$ DVs for HNLs with various masses.
This paper presents a first measurement of the cross-section for the charged-current Drell-Yan process $pp\rightarrow W^{\pm} \rightarrow \ell^{\pm} ν$ above the resonance region, where $\ell$ is an electron or muon. The measurement is performed for transverse masses, $m_{\text{T}}^{\text{W}}$, between 200 GeV and 5000 GeV, using a sample of 140 fb$^{-1}$ of $pp$ collision data at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV collected by the ATLAS detector at the LHC during 2015-2018. The data are presented single differentially in transverse mass and double differentially in transverse mass and absolute lepton pseudorapidity. A test of lepton flavour universality shows no significant deviations from the Standard Model. The electron and muon channel measurements are combined to achieve a total experimental precision of 3% at low $m_{\text{T}}^{\text{W}}$. The single- and double differential $W$-boson charge asymmetries are evaluated from the measurements. A comparison to next-to-next-to-leading-order perturbative QCD predictions using several recent parton distribution functions and including next-to-leading-order electroweak effects indicates the potential of the data to constrain parton distribution functions. The data are also used to constrain four fermion operators in the Standard Model Effective Field Theory formalism, in particular the lepton-quark operator Wilson coefficient $c_{\ell q}^{(3)}.$
The interaction between pions and nucleons plays a crucial role in hadron physics. It represents a fundamental building block of the low-energy QCD dynamics and is subject to several resonance excitations. This work studies the p-$\pi^{\pm}$ dynamics using femtoscopic correlations in high-multiplicity pp collisions at $\sqrt{s} = 13$ TeV measured by ALICE at the LHC. As the final-state interaction between protons and pions is well constrained by scattering experiments and the study of pionic hydrogen, the results give access to information on the particle-emitting source in pp collisions using the femtoscopy methods. The scaling of the source size of primordial protons and pions against their pair transverse mass is extracted. The results are compared with the source sizes studied with p-p, p-K$^+$, and $\pi^{\pm}$-$\pi^{\pm}$ pairs by ALICE in the same collision system and are found to be in agreement for the different particle pairs. This reinforces recent findings by ALICE of a common emission source for all hadron-pairs in pp collisions at LHC energies. Furthermore, the p-p-$\pi^{\pm}$ systems are studied using three-particle femtoscopy in pp collisions at $\sqrt{s} = 13$ TeV. The presence of three-body effects is analyzed utilizing the cumulant expansion method. In this formalism, the known two-body interactions are subtracted in order to isolate the three-body effects. For both, p-p-$\pi^{+}$ and p-p-$\pi^{-}$, a non-zero cumulant is found, indicating effects beyond pairwise interactions. These results give information on the coupling of the pion to multiple nucleons.
p-$\pi^{+}$ + antip-$\pi^{-}$ correlation function in high-multiplicity (0-0.17%) pp collisions at $\sqrt{s}=13$ TeV for $m_\text{T} \in [0.54, 0.75)$ GeV/$c^2$
p-$\pi^{+}$ + antip-$\pi^{-}$ correlation function in high-multiplicity (0-0.17%) pp collisions at $\sqrt{s}=13$ TeV for $m_\text{T} \in [0.75, 0.95)$ GeV/$c^2$
p-$\pi^{+}$ + antip-$\pi^{-}$ correlation function in high-multiplicity (0-0.17%) pp collisions at $\sqrt{s}=13$ TeV for $m_\text{T} \in [0.95, 1.20)$ GeV/$c^2$
This paper presents the primary charged-particle multiplicity distributions in proton-lead collisions at a centre-of-mass energy per nucleon-nucleon collision of $\sqrt{s_{\rm NN}} = 5.02$ TeV. The distributions are reported for non-single diffractive collisions in different pseudorapidity ranges. The measurements are performed using the combined information from the Silicon Pixel Detector and the Forward Multiplicity Detector of ALICE. The multiplicity distributions are parametrised with a double negative binomial distribution function which provides satisfactory descriptions of the distributions for all the studied pseudorapidity intervals. The data are compared to models and analysed quantitatively, evaluating the first four moments (mean, standard deviation, skewness, and kurtosis). The shape evolution of the measured multiplicity distributions is studied in terms of KNO variables and it is found that none of the considered models reproduces the measurements. This paper also reports on the average charged-particle multiplicity, normalised by the average number of participating nucleon pairs, as a function of the collision energy. The multiplicity results are then compared to measurements made in proton-proton and nucleus-nucleus collisions across a wide range of collision energies.
Charged-particle multiplicity distributions for different pseudorapidity intervals measured in NSD p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.
The pseudorapidity dependence of the double NBD parameters $\langle n \rangle_1$, $\langle n \rangle_2$, $k_1$, and $k_2$ in NSD p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.
First four moments ($\langle N_{\mathrm{ch}}\rangle$, $\sigma$, $S$, and $\kappa$) of charged-particle multiplicity distributions for different pseudorapidity intervals in NSD p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.
This paper presents a search for massive, charged, long-lived particles with the ATLAS detector at the Large Hadron Collider using an integrated luminosity of 140 $fb^{-1}$ of proton-proton collisions at $\sqrt{s}=13$ TeV. These particles are expected to move significantly slower than the speed of light. In this paper, two signal regions provide complementary sensitivity. In one region, events are selected with at least one charged-particle track with high transverse momentum, large specific ionisation measured in the pixel detector, and time of flight to the hadronic calorimeter inconsistent with the speed of light. In the other region, events are selected with at least two tracks of opposite charge which both have a high transverse momentum and an anomalously large specific ionisation. The search is sensitive to particles with lifetimes greater than about 3 ns with masses ranging from 200 GeV to 3 TeV. The results are interpreted to set constraints on the supersymmetric pair production of long-lived R-hadrons, charginos and staus, with mass limits extending beyond those from previous searches in broad ranges of lifetime.
The contour for the excluded mass--lifetime region for stau pair production obtained with the di-track search. All masses and lifetimes shown that are below the curve and above 200 GeV are excluded by the observed data (while the expected exclusion is between the upper curve down to 210 GeV for lifetimes above 3000 ns). The sensitivity extends indefinitely to longer lifetimes.
The contour for the excluded mass--lifetime region for stau pair production obtained with the di-track search. All masses and lifetimes shown that are below the curve and above 200 GeV are excluded by the observed data (while the expected exclusion is between the upper curve down to 210 GeV for lifetimes above 3000 ns). The sensitivity extends indefinitely to longer lifetimes.
The contour for the excluded mass--lifetime region for stau pair production obtained with the di-track search. All masses and lifetimes shown that are below the curve and above 200 GeV are excluded by the observed data (while the expected exclusion is between the upper curve down to 210 GeV for lifetimes above 3000 ns). The sensitivity extends indefinitely to longer lifetimes.
Correlations between event-by-event fluctuations of anisotropic flow harmonics are measured in Pb-Pb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV, as recorded by the ALICE detector at the LHC. This study presents correlations up to the hexagonal flow harmonic, $v_6$, which was measured for the first time. The magnitudes of these higher-order correlations are found to vary as a function of collision centrality and harmonic order. These measurements are compared to viscous hydrodynamic model calculations with EKRT initial conditions and to the iEBE-VISHNU model with TRENTo initial conditions. The observed discrepancies between the data and the model calculations vary depending on the harmonic combinations. Due to the sensitivity of model parameters estimated with Bayesian analyses to these higher-order observables, the results presented in this work provide new and independent constraints on the initial conditions and transport properties in theoretical models used to describe the system created in heavy-ion collisions.
NSC(5,2) vs centrality in Pb-Pb collisions at 5.02 TeV
NSC(5,3) vs centrality in Pb-Pb collisions at 5.02 TeV
NSC(6,2) vs centrality in Pb-Pb collisions at 5.02 TeV
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