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

New constraints for QCD matter from improved Bayesian parameter estimation in heavy-ion collisions at LHC

The transport properties of quark-gluon plasma created in relativistic heavy-ion collisions are quantified by an improved global Bayesian analysis using the CERN Large Hadron Collider Pb-Pb data at root s(NN) = 2.76 and 5.02 TeV. The results show that the uncertainty of the extracted transport coefficients is significantly reduced by including new sophisticated collective flow observables from two collision energies for the first time. This work reveals the stronger temperature dependence of specific shear viscosity, a lower value of specific bulk viscosity, and a higher hadronization switching temperature than in the previous studies. The sensitivity analysis confirms that the precision measurements of higher-order harmonic flow and their correlations are crucial in extracting accurate values of the transport properties. (C) 2022 The Author(s). Published by Elsevier B.V.Peer reviewe

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.Peer reviewe

First measurement of the vertical bar t vertical bar-dependence of coherent J/psi photonuclear production

The first measurement of the cross section for coherent J/Psi photoproduction as a function of vertical bar t vertical bar, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pbcollisions at a centre-of-mass energy per nucleon pair root s(NN) = 5.02 TeV with the J/Psi produced in the central rapidity region vertical bar y vertical bar < 0.8, which corresponds to the small Bjorken-xrange (0.3 - 1.4) x 10(-3). The measured vertical bar t vertical bar-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x. (C) 2021 The Author(s). Published by Elsevier B.V.Peer reviewe

Multiharmonic Correlations of Different Flow Amplitudes in Pb-Pb Collisions at root s(NN)=2.76 TeV

The event-by-event correlations between three flow amplitudes are measured for the first time in Pb-Pb collisions, using higher-order symmetric cumulants. We find that different three-harmonic correlations develop during the collective evolution of the medium when compared to correlations that exist in the initial state. These new results cannot be interpreted in terms of previous lower-order flow measurements since contributions from two-harmonic correlations are explicitly removed in the new observables. A comparison to Monte Carlo simulations provides new and independent constraints for the initial conditions and system properties of nuclear matter created in heavy-ion collisions.Peer reviewe

Measurement of beauty and charm production in pp collisions at s√ = 5.02 TeV via non-prompt and prompt D mesons

The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at root s = 13 TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (dN(ch)/d eta similar to 26) as measured in p-Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p-Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and statistical hadronisation models (SHM).Peer reviewe

Charm-quark fragmentation fractions and production cross section at midrapidity in pp collisions at the LHC

Peer reviewe

Experimental Evidence for an Attractive p-phi Interaction

This Letter presents the first experimental evidence of the attractive strong interaction between a proton and a phi meson. The result is obtained from two-particle correlations of combined p-phi circle plus (p) over bar-phi pairs measured in high-multiplicity pp collisions at root s = 13 TeV by the ALICE Collaboration. The spin-averaged scattering length and effective range of the p-phi interaction are extracted from the fully corrected correlation function employing the Lednicky-Lyuboshits approach. In particular, the imaginary part of the scattering length vanishes within uncertainties, indicating that inelastic processes do not play a prominent role for the p-phi interaction. These data demonstrate that the interaction is dominated by elastic p-phi scattering. Furthermore, an analysis employing phenomenological Gaussian-and Yukawa-type potentials is conducted. Under the assumption of the latter, the N-phi coupling constant is found to be g(N-phi) = 0.14 +/- 0.03(stat) +/- 0.02(syst). This work provides valuable experimental input to accomplish a self-consistent description of the N-phi interaction, which is particularly relevant for the more fundamental studies on partial restoration of chiral symmetry in nuclear medium.Peer reviewe

Charged-particle multiplicity fluctuations in Pb-Pb collisions at root s(NN)=2.76 TeV

Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb-Pb collisions at root s(NN) = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range |eta| < 0.8 and transverse momentum 0.2 < p(T) < 2.0 GeV/c. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of themultiplicity distribution. The. and p(T) dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb-Pb collisions.Peer reviewe

Measurement of the production cross section of prompt Xi(0)(c) baryons at midrapidity in pp collisions at root s=5.02 TeV

The transverse momentum (p(T)) differential cross section of the charm-strange baryon Xi(0)(c) is measured at midrapidity (vertical bar y vertical bar < 0.5) via its semileptonic decay into e(+)Xi(-)nu(e) in pp collisions at root s = 5.02TeV with the ALICE detector at the LHC. The ratio of the p(T)-differential Xi(0)(c)-baryon and D-0-meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 event generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The pT-integrated cross section of prompt Xi(0)(c)-baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio Xi(0)(c)/D-0 = 0.20 +/- 0.04 (stat.)(-0.07)(+0.08) (syst.). These results provide an additional indication of a modification of the charm fragmentation from e(+) e(-) and e-p collisions to pp collisions.Peer reviewe