Characterizing the initial conditions of heavy-ion collisions at the LHC with mean transverse momentum and anisotropic flow correlations

TL;DR

This study measures correlations between mean transverse momentum and flow coefficients in heavy-ion collisions, comparing results with hydrodynamic models to better understand initial conditions and the quark-gluon plasma.

Contribution

First measurement of higher-order correlations between mean transverse momentum and flow coefficients in Pb-Pb and Xe-Xe collisions, providing new insights into initial state characterization.

Findings

Data favor IP-Glasma initial state over T_RenTo models.

Higher-order correlations show anticorrelation, constraining initial state models.

Hydrodynamic models with IP-Glasma better reproduce observed correlations.

Abstract

Correlations between mean transverse momentum $[p_{\rm T}]$ and anisotropic flow coefficients $v_{\rm 2}$ or $v_{\rm 3}$ are measured as a function of centrality in Pb$-$Pb and Xe$-$Xe collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and 5.44 TeV, respectively, with ALICE. In addition, the recently proposed higher-order correlation between $[p_{\rm T}]$, $v_{\rm 2}$, and $v_{\rm 3}$ is measured for the first time, which shows an anticorrelation for the presented centrality ranges. These measurements are compared with hydrodynamic calculations using IP-Glasma and $\rm T_{R}ENTo$ initial-state shapes, the former based on the Color Glass Condensate effective theory with gluon saturation, and the latter a parameterized model with nucleons as the relevant degrees of freedom. The data are better described by the IP-Glasma rather than the $\rm T_{R}ENTo$ based calculations. In particular, Trajectum and JETSCAPE predictions, both based on the $\rm T_{R}ENTo$ initial state model but with different parameter settings, fail to describe the measurements. As the correlations between $[p_{\rm T}]$ and $v_{\rm n}$ are mainly driven by the correlations of the size and the shape of the system in the initial state, these new studies pave a novel way to characterize the initial state and help pin down the uncertainty of the extracted properties of the quark$-$gluon plasma recreated in relativistic heavy-ion collisions.