Bayesian estimation of the specific shear and bulk viscosity of the quark-gluon plasma with additional flow harmonic observables

The transport properties of the strongly coupled quark-gluon plasma created in ultrarelativistic heavy-ion collisions are extracted by Bayesian parameter estimate methods with the latest collision beam energy data from the CERN Large Hadron Collider. This Bayesian analysis includes sophisticated flow harmonic observables for the first time. We found that the temperature dependence of specific shear viscosity appears weaker than in the previous studies. The results prefer a lower value of specific bulk viscosity and a higher switching temperature to reproduce additional observables. However, the improved statistical uncertainties both on the experimental data and hydrodynamic calculations with additional observables do not help to reduce the final credibility ranges much, indicating a need for improving the dynamical collision model before the hydrodynamic takes place. In addition, the sensitivities of experimental observables to the parameters in hydrodynamic model calculations are quantified. It is found that the analysis benefits most from the symmetric cumulants and nonlinear flow modes, which mostly reflect nonlinear hydrodynamic responses, in constraining the temperature dependence of the specific shear and bulk viscosities in addition to the previously used flow coefficients.Peer reviewe

Probing the Effects of Strong Electromagnetic Fields with Charge-Dependent Directed Flow in Pb-Pb Collisions at the LHC

The first measurement at the LHC of charge-dependent directed flow (v(1)) relative to the spectator plane is presented for Pb-Pb collisions at root s(NN) = 5.02 TeV. Results are reported for charged hadrons and D-0 mesons for the transverse momentum intervals p(T) > 0.2 GeV/c and 3 <p(T) <6 GeV/c in the 5%-40% and 10%-40% centrality classes, respectively. The difference between the positively and negatively charged hadron v(1) has a positive slope as a function of pseudorapidity eta, d Delta v(1)/d eta = [1.68 +/- 0.49(stat) +/- 0.41(syst)] x 10(-4). The same measurement for D-0 and (D) over bar (0) mesons yields a positive value d Delta v(1)/d eta = [4.9 +/- 1.7(stat)] +/- 0.6(syst)] x 10(-1), which is about 3 orders of magnitude larger than the one of the charged hadrons. These measurements can provide new insights into the effects of the strong electromagnetic field and the initial tilt of matter created in noncentral heavy ion collisions on the dynamics of light (u, d, and s) and heavy (c) quarks. The large difference between the observed Delta v(1) of charged hadrons and D-0 mesons may reflect different sensitivity of the charm and light quarks to the early time dynamics of a heavy ion collision. These observations challenge some recent theoretical calculations, which predicted a negative and an order of magnitude smaller value of d Delta v(1)/d eta for both light flavor and charmed hadrons.Peer reviewe

J/psi production as a function of charged-particle multiplicity in p-Pb collisions at root s(NN)=8.16 TeV

Inclusive J/psi yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pairs root s(NN) = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/psi mesons are reconstructed at forward (2.03<y(cms)Peer reviewe

One-dimensional charged kaon femtoscopy in p-Pb collisions at root s(NN)=5.02 TeV

The correlations of identical charged kaons were measured in p-Pb collisions at root s(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 root s = 7 TeV and root s(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 3 hadronic interaction model and disfavor models with large initial size or strong collective expansion at low multiplicities.Peer reviewe

Study of the Lambda-Lambda interaction with femtoscopy correlations in pp and p-Pbcollisions at the LHC

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 root s = 13 TeV and p-Pb collisions at root s(NN) = 5.02 TeV, combined with previously published results from pp collisions at root 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(-2.4)(+1.6)(stat)(-1.0)(+1.8)(syst) MeV. (C) 2019 The Author(s). Published by Elsevier B.V.Peer reviewe

Charged-particle pseudorapidity density at mid-rapidity in p-Pb collisions at root S-NN=8.16 TeV

The pseudorapidity density of charged particles, dN(ch)/d eta, in p-Pb collisions has been measured at a centre of-mass energy per nucleon-nucleon pair of root S-NN = 8.16 TeV at mid-pseudorapidity for non-single-diffractive events. The results cover 3.6 units of pseudorapidity, vertical bar eta vertical bar /2 is 4.73 +/- 0.20, where is the average number of participating nucleons, is 9.5% higher than the corresponding value for p-Pb collisions at root S-NN = 5.02 TeV. Measurements are compared with models based on different mechanisms for particle production. All models agree within uncertainties with data in the Pb-going side, while HIJING overestimates, showing a symmetric behaviour, and EPOS underestimates the p-going side of the dN(ch)/d eta distribution. Saturation-based models reproduce the distributions well for eta > -1.3. The dN(ch)/d eta is also measured for different centrality estimators, based both on the charged particle multiplicity and on the energy deposited in the Zero Degree Calorimeters. A study of the implications of the large multiplicity fluctuations due to the small number of participants for systems like p-Pb in the centrality calculation for multiplicity-based estimators is discussed, demonstrating the advantages of determining the centrality with energy deposited near beam rapidity.Peer reviewe

Lambda(+)(C) production in pb-pb collisions at root S-NN=5.02 TeV

A measurement of the production of prompt Lambda(+)(C) baryons in Pb-Pb collisions at root S-NN = 5.02 TeV with the ALICE detector at the LHC is reported. The Lambda(+)(C) and (Lambda) over bar (-)(C) were reconstructed at midrapidity (vertical bar y vertical bar pK(S)(0) (and charge conjugate) in the transverse momentum and centrality intervals 6 < p(T) < 12 GeV/c and 0-80%. The Lambda(+)(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 root s = 7 TeV and in p-Pb collisions at root S-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 in the common P-T interval covered by the measurements in the two collision systems. The Lambda(+)(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(+)(C) nuclear modification factor, R-AA, is also presented. The measured values of the R-AA of Lambda(+)(C), D-S(+) and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy (R-AA(D0) < R-AA(DS+) < R-AA(Lambda C+)), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium. (C) 2019 European Organization for Nuclear Research. Published by Elsevier B.V.Peer reviewe