Characterizing the initial state and dynamical evolution in XeXe and PbPb collisions using multiparticle cumulants

TL;DR

This study measures multiparticle correlations among flow harmonics in XeXe and PbPb collisions to probe initial-state geometry fluctuations and the nonlinear hydrodynamic response of the quark-gluon plasma.

Contribution

It provides the first measurements of mixed-order moments of flow harmonics in XeXe collisions, comparing them with PbPb results to explore nuclear deformation effects.

Findings

Correlations among flow harmonics reveal sensitivity to initial geometry fluctuations.

Results constrain initial-state model parameters affecting QGP evolution.

Measurements highlight the importance of higher-order flow harmonics in hydrodynamic modeling.

Abstract

For the first time, correlations among mixed-order moments of two or three flow harmonics$-$($v_{n}^{k},v_{m}^{l}$) and ($v_{n}^{k},v_{m}^{l}, v_{p}^{q}$), with $k$, $l$, and $q$ denoting the respective orders$-$are measured in xenon-xenon (XeXe) collisions and compared with lead-lead (PbPb) results, providing a novel probe of collective behavior in heavy ion collisions. These measurements compare a nearly spherical, doubly-magic ${}^{208}$Pb nucleus to a triaxially deformed ${}^{129}$Xe nucleus, emphasizing the sensitivity to initial-state geometry fluctuations arising from nuclear deformation. The dependence of these results ($v_{n}$, $n$ = 2, 3, 4) on the shape and size of the nuclear overlap region is studied. Comparisons between $v_{2}$, $v_{3}$, and $v_{4}$ demonstrate the importance of $v_{3}$ and $v_{4}$ in exploring the nonlinear hydrodynamic response of the quark-gluon plasma (QGP) to the initial spatial anisotropy. The results constrain initial-state model parameters that influence the evolution of the QGP. The CMS detector was used to collect XeXe and PbPb data at nucleon-nucleon center-of-mass energies of $\sqrt{s_\mathrm{NN}}$ = 5.44 and 5.36 TeV, respectively. Correlations are extracted using multiparticle mixed-harmonic cumulants (up to eight-particle cumulants) with charged particles in the pseudorapidity range $\lvert\eta\rvert$ $\lt$ 2.4 and transverse momentum range 0.5 $\lt$ $p_\mathrm{T}$ $\lt$ 3 GeV/$c$.