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

Abstract

For the first time, correlations among mixed-order moments of two or three flow harmonics —(v^k_η, v^l_m) and ((v^k_η, 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 ²⁰⁸Pb nucleus to a triaxially deformed ¹²⁹Xe nucleus, emphasizing the sensitivity to initial-state geometry fluctuations arising from nuclear deformation. The dependence of these results (v_n, η = 1, 2, 3) on the shape and size of the nuclear overlap region is studied. Comparisons between v₂, v₃, and v₄ demonstrate the importance of v₃ and v₄ 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 √𝒔_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 |η| < 2.4 and transverse momentum range 0.5 < p_T < 3 GeV/c.