J/psi Elliptic Flow in Pb-Pb Collisions at root s(NN)=5.02 TeV

We report a precise measurement of the J/psi elliptic flow in Pb-Pb collisions at root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The J/psi mesons are reconstructed at midrapidity (|y| < 0.9) in the dielectron decay channel and at forward rapidity (2.5 < y < 4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v(2) of the J/psi is studied as a function of the transverse momentum and centrality. A positive v(2) is observed in the transverse momentum range 2<p(T)<8GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at root s(NN) = 2.76 TeV in semicentral collisions. At midrapidity, the J/psi v(2) is investigated as a function of the transverse momentum in semicentral collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low p(T) the elliptic flow of the J/psi originates from the thermalization of charm quarks in the deconfined medium but suggests that additional mechanisms might be missing in the models

Production of omega mesons in pp collisions at s=7 TeV

The invariant differential cross section of inclusive omega (782) meson production at midrapidity (|y| pi+pi-pi 0 decay channel. The measured omega production cross section is compared to various calculations: PYTHIA 8.2 Monash 2013 describes the data, while PYTHIA 8.2 Tune 4C overestimates the data by about 50%. A recent NLO calculation, which includes a model describing the fragmentation of the whole vector-meson nonet, describes the data within uncertainties below 6 GeV/c, while it overestimates the data by up to 50% for higher pT. The omega/pi 0 ratio is in agreement with previous measurements at lower collision energies and the PYTHIA calculations. In addition, the measurement is compatible with transverse mass scaling within the measured pT range and the ratio is constant with C omega/pi 0=0.67 +/- 0.03(stat) +/- 0.04(sys) above a transverse momentum of 2.5 GeV/c

Non-linear flow modes of identified particles in Pb-Pb collisions at root s(NN)=5.02 TeV with the ALICE detector

The non-linear flow modes, v(4,22), v(5,32) and v(6,33) as a function of transverse momentum (p(T)) have been measured for the first time in Pb-Pb collisions at root s(NN) = 5.02 TeV for identified particles, i.e. charged pions, kaons and (anti-)protons. These observables probe the contribution of the second and third initial anisotropy coefficients to the higher order flow harmonics. Interestingly, all the characteristic features observed in previous p(T)-differential as well as p(T)-integrated measurements (e.g. v(2) and v(3)) for various particle species are present in these measurements, i.e. increase of magnitude with increasing centrality percentile, a mass ordering in the low p(T) region and a particle type grouping in the intermediate p(T) region. The results cover 0-1% (ultra-central collisions), 10-20% (mid-central collisions) and 40-50% (mid-peripheral collisions) centrality intervals and allow to test models that attempt to describe initial conditions and the mode-coupling of different harmonics

Measurements of mixed harmonic cumulants in Pb-Pb collisions at root s(NN)=5.02 TeV

Correlations between moments of different flow coefficients are measured in Pb-Pb collisions at root s(NN) = 5.02 TeV recorded with the ALICE detector. These new measurements are based on multiparticle mixed harmonic cumulants calculated using charged particles in the pseudorapidity region vertical bar eta vertical bar < 0.8 with the transverse momentum range 0.2 < p(T) < 5.0 GeV/c. The centrality dependence of correlations between two flow coefficients as well as the correlations between three flow coefficients, both in terms of their second moments, are shown. In addition, a collection of mixed harmonic cumulants involving higher moments of v(2) and v(3) is measured for the first time, where the characteristic signature of negative, positive and negative signs of four-, six- and eight-particle cumulants are observed, respectively. The measurements are compared to the hydrodynamic calculations using iEBE-VISHNU with AMPT and TRENTo initial conditions. It is shown that the measurements carried out using the LHC Run 2 data in 2015 have the precision to explore the details of initial-state fluctuations and probe the nonlinear hydrodynamic response of v(2) and v(3) to their corresponding initial anisotropy coefficients epsilon(2) and epsilon(3). These new studies on correlations between three flow coefficients as well as correlations between higher moments of two different flow coefficients will pave the way to tighten constraints on initial-state models and help to extract precise information on the dynamic evolution of the hot and dense matter created in heavy-ion collisions at the LHC. (C) 2021 The Author. Published by Elsevier B.V

Elliptic flow of identified hadrons in small collisional systems measured with ALICE

Recent observations of long-range multi-particle azimuthal correlations in p-Pb and high multiplicity pp collisions provided new insights into collision dynamics and opened a possibility to study collective effects in these small systems. New measurements of p(T)-differential elliptic flow (v(2)) coefficient for inclusive charged hadrons as well as a variety of identified particle species in p-Pb collisions at root s(NN) = 5.02 TeV are presented. The data was collected by ALICE during the LHC Run 2 data taking. Besides high precision measurements of v(2)(P-T) for pi(+/-), K-+/- and p((p) over bar), the first results for K-s(0), Lambda((Lambda) over bar) and phi are shown. In order to eliminate non-flow contamination, a pseudorapidity separation between correlated particles is applied as well as subtraction of remaining non-flow estimate based on a measurement of minimum-bias pp collisions at root s = 13 TeV. Moreover, the reported characteristic mass ordering and approximate number of constituent quarks (NCQ) and transverse kinetic energy (KET) scaling of v(2) allow to test various theoretical models, constrain the initial conditions, and probe the origin of collective behavior in small collision systems