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

For the first time, correlations among mixed-order moments of two or three flow harmonics -($v$$^k_n$, $v$$^l_m$) and ($v$$^k_n$, $v$$^l_m$, $v$$^q_p$), 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 $\sqrt{S_{NN}}$ = 5.44 and 5.36 TeV, respectively. ... mehrCorrelations are extracted using multiparticle mixed-harmonic cumulants (up to eight-particle cumulants) with charged particles in the pseudorapidity range |η| < 2.4 and transverse momentum range 0.5 < p$_T$ < 3 GeV/c.