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.
Understanding nuclear structure provides essential insights into the properties of atomic nuclei. In this paper, details of the nuclear structure of $^{\rm 129}$Xe, such as the quadrupole deformation and the nuclear diffuseness, are studied by extensive measurements of anisotropic-flow-related observables in Xe$-$Xe collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.44$ TeV with the ALICE detector at the LHC. The results are compared with those from Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV for a baseline, given that the $^{\rm 208}$Pb nucleus is not deformed. Furthermore, comprehensive comparisons are performed with a state-of-the-art hybrid model using IP-Glasma+MUSIC+UrQMD. It is found that among various IP-Glasma+MUSIC+UrQMD calculations with different values of nuclear parameters, the one using a nuclear diffuseness parameter of $a_0=0.492$ and a nuclear quadrupole deformation parameter of $\beta_2=0.207$ provides a better description of the presented flow measurements. These studies represent an important step towards a thorough exploration of the imaging power of nuclear collisions at ultrarelativistic energy and the search for the imprint of nuclear structure on various flow observables in heavy-ion collisions at the LHC. The findings demonstrate the potential of nuclear structure studies at the TeV energy scale and highlight that the LHC experiments can complement existing low-energy experiments on nuclear structure studies.
Charged particle $v_2\{2, \left | \Delta\eta \right | > 1.0\}$ as a function of centrality in Xe$-$Xe and Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.44 TeV and $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, respectively.
Charged particle $v_2\{4\}$ as a function of centrality in Xe$-$Xe and Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.44 TeV and $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, respectively.
Ratio between Xe$-$Xe and Pb$-$Pb charged particle $v_2\{2, \left | \Delta\eta \right | > 1.0\}$ as a function of centrality.
Multiplicity ($N_{\rm ch}$) distributions and transverse momentum ($p_{\rm T}$) spectra of inclusive primary charged particles in the kinematic range of $|\eta| < 0.8$ and 0.15 GeV/$c$$< p_{T} <$ 10 GeV/$c$ are reported for pp, p-Pb, Xe-Xe and Pb-Pb collisions at centre-of-mass energies per nucleon pair ranging from $\sqrt{s_{\rm NN}} = 2.76$ TeV up to $13$ TeV. A sequential two-dimensional unfolding procedure is used to extract the correlation between the transverse momentum of primary charged particles and the charged-particle multiplicity of the corresponding collision. This correlation sharply characterises important features of the final state of a collision and, therefore, can be used as a stringent test of theoretical models. The multiplicity distributions as well as the mean and standard deviation derived from the $p_{\rm T}$ spectra are compared to state-of-the-art model predictions. Providing these fundamental observables of bulk particle production consistently across a wide range of collision energies and system sizes can serve as an important input for tuning Monte Carlo event generators.
Charged-particle multiplicity distribution for pp collisions at 2.76 TeV.
Charged-particle multiplicity distribution for pp collisions at 2.76 TeV.
Koba-Nielsen-Olesen scaled charged-particle multiplicity distribution for pp collisions at 2.76 TeV.
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 $5 < p_{\rm T}^{\rm assoc} < 7$ ${\rm GeV}/c$.
The first measurements of elliptic flow of $\pi^\pm$, ${\rm K}^\pm$, p+$\overline{\rm p}$, ${\rm K_{S}^0}$, $\Lambda$+$\overline{\Lambda}$, $\phi$, $\Xi^-$+$\Xi^+$, and $\Omega^-$+$\Omega^+$ using multiparticle cumulants in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. Results obtained with two- ($v_2\{2\}$) and four-particle cumulants ($v_2\{4\}$) are shown as a function of transverse momentum, $p_{\rm T}$, for various collision centrality intervals. Combining the data for both $v_2\{2\}$ and $v_2\{4\}$ also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark-gluon plasma. The characteristic features observed in previous $p_{\rm T}$-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low $p_{\rm T}$ and the approximate scaling with the number of constituent quarks at intermediate $p_{\rm T}$, are similarly present in the four-particle correlations and the combinations of $v_2\{2\}$ and $v_2\{4\}$. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide $p_{\rm T}$ range.
The correlations between event-by-event fluctuations of symmetry planes are measured in Pb--Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV recorded by the ALICE detector at the Large Hadron Collider. This analysis is conducted using the Gaussian Estimator technique, which is insensitive to biases from correlations between different flow amplitudes. The study presents, for the first time, the centrality dependence of correlations involving up to five different symmetry planes. The correlation strength varies depending on the harmonic order of the symmetry plane and the collision centrality. Comparisons with measurements from lower energies indicate no significant differences within uncertainties. Additionally, the results are compared with hydrodynamic model calculations. Although the model predictions provide a qualitative explanation of the experimental results, they overestimate the data for some observables. This is particularly true for correlators that are sensitive to the non-linear response of the medium to initial-state anisotropies in the collision system. As these new correlators provide unique information -- independent of flow amplitudes -- their usage in future model developments can further constrain the properties of the strongly-interacting matter created in ultrarelativistic heavy-ion collisions.
Centrality dependence of $\langle\cos[6(\Psi_3-\Psi_2)]\rangle$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
Centrality dependence of $\langle\cos[4(\Psi_4-\Psi_2)]\rangle$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
Centrality dependence of $\langle\cos[8(\Psi_4-\Psi_2)]\rangle$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
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
The production yields of non-prompt $\mathrm{D_s}^{+}$ mesons, namely $\mathrm{D_s}^{+}$ mesons from beauty-hadron decays, were measured for the first time as a function of the transverse momentum ($p_{\rm T}$) at midrapidity ($|y|<0.5$) in central and semi-central Pb$-$Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV with the ALICE experiment at the LHC. The $\mathrm{D_s}^{+}$ mesons and their charge conjugates were reconstructed from the hadronic decay channel $\mathrm{D_s}^{+} \to \phi\pi^+$, with $\phi \to {\rm K}^-{\rm K}^+$, in the $4 < p_{\rm T}<36$ GeV/$c$ and $2 < p_{\rm T}<24$ GeV/$c$ intervals for the 0$-$10% and 30$-$50% centrality classes, respectively. The measured yields of non-prompt $\mathrm{D_s}^{+}$ mesons are compared to those of prompt $\mathrm{D_s}^{+}$ and non-prompt $\mathrm{D^0}$ mesons by calculating the ratios of the production yields in Pb$-$Pb collisions and the nuclear modification factor $R_\mathrm{AA}$. The ratio between the $R_\mathrm{AA}$ of non-prompt $\mathrm{D_s}^{+}$ and prompt $\mathrm{D_s}^{+}$ mesons, and that between the $R_\mathrm{AA}$ of non-prompt $\mathrm{D_s}^{+}$ and non-prompt $\mathrm{D^0}$ mesons in central Pb$-$Pb collisions are found to be on average higher than unity in the $4< p_{\rm T}<12$ GeV/$c$ interval with a statistical significance of about $1.6\,\sigma$ and $1.7\,\sigma$, respectively. The measured $R_\mathrm{AA}$ ratios are compared with the predictions of theoretical models of heavy-quark transport in a hydrodynamically expanding QGP that incorporate hadronisation via quark recombination.
Production yield of non-prompt $\mathrm{D}_{s}^{\pm}$ candidates average for 0-10% Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.
Production yield of non-prompt $\mathrm{D}_{s}^{\pm}$ candidates average for 30-50% Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.
Yield ratio of non-prompt over prompt $\mathrm{D}_{s}^{+}$ for 0-10% Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.
An excess of J/$\psi$ yield at very low transverse momentum ($p_{\rm T} < 0.3$ GeV/$c$), originating from coherent photoproduction, is observed in peripheral and semicentral hadronic Pb$-$Pb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV. The measurement is performed with the ALICE detector via the dimuon decay channel at forward rapidity ($2.5<y<4$). The nuclear modification factor at very low $p_{\rm T}$ and the coherent photoproduction cross section are measured as a function of centrality down to the 10% most central collisions. These results extend the previous study at $\sqrt{s_{\rm NN}} = 2.76$ TeV, confirming the clear excess over hadronic production in the $p_{\rm T}$ range 0$-$0.3 GeV/$c$ and the centrality range 70$-$90%, and establishing an excess with a significance greater than 5$\sigma$ also in the 50$-$70% and 30$-$50% centrality ranges. The results are compared with earlier measurements at $\sqrt{s_{\rm NN}} = 2.76$ TeV and with different theoretical predictions aiming at describing how coherent photoproduction occurs in hadronic interactions with nuclear overlap.
J/$\psi$ nuclear modification factor as a function of $\langle N_{\rm part}\rangle$ measured in the rapidity range 2.5 < y < 4 for $p_{\rm T}$ < 0.3 GeV/c. The centrality-correlated uncertainty of 7.2% is not included.
J/$\psi$ nuclear modification factor as a function of $\langle N_{\rm part} \rangle$ measured in the rapidity range 2.5 < y < 4 for 0.3 < $p_{\rm T}$ < 1 GeV/c. The centrality-correlated uncertainty of 6.6% is not included.
J/$\psi$ nuclear modification factor as a function of $\langle N_{\rm part} \rangle$ measured in the rapidity range 2.5 < y < 4 for 1 < $p_{\rm T}$ < 2 GeV/c. The centrality-correlated uncertainty of 6.2% is not included.
The study of the azimuthal anisotropy of inclusive muons produced in p-Pb collisions at $\sqrt{s_{\rm NN}} = 8.16$ TeV, using the ALICE detector at the LHC is reported. The measurement of the second-order Fourier coefficient of the particle azimuthal distribution, $v_2$, is performed as a function of transverse momentum $p_{\rm T}$ in the 0-20% high-multiplicity interval at both forward ($2.03 < y_{\rm CMS} < 3.53$) and backward ($-4.46 < y_{\rm CMS} < -2.96$) rapidities over a wide $p_{\rm T}$ range, $0.5 < p_{\rm T} < 10$ GeV/$c$, in which a dominant contribution of muons from heavy-flavour hadron decays is expected at $p_{\rm T} > 2$ GeV/$c$. The $v_2$ coefficient of inclusive muons is extracted using two different techniques, namely two-particle cumulants, used for the first time for heavy-flavour measurements, and forward-central two-particle correlations. Both techniques give compatible results. A positive $v_2$ is measured at both forward and backward rapidities with a significance larger than $4.7\sigma$ and $7.6\sigma$, respectively, in the interval $2 < p_{\rm T} < 6$ GeV/$c$. Comparisons with previous measurements in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, and with AMPT and CGC-based theoretical calculations are discussed. The findings impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems.
Inclusive muon $v_{2}^{\mu}$ as a function of $p_{\mathrm{T}}$ is measured by two-particle correlation method at forward rapidities in high-multiplicity (0$-$20%) p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$= 8.16 TeV. The event activity is estimated with the V0M estimator.
Inclusive muon $v_{2}^{\mu}$ as a function of $p_{\mathrm{T}}$ is measured by two-particle cumulant method at forward rapidities in high-multiplicity (0$-$20%) p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$= 8.16 TeV. The event activity is estimated with the V0M estimator.
Inclusive muon $v_{2}^{\mu}$ as a function of $p_{\mathrm{T}}$ is measured by two-particle correlation method at backward rapidities in high-multiplicity (0$-$20%) p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$= 8.16 TeV. The event activity is estimated with the V0M estimator.
Forum