Abstract
Measurements of elliptic (v2) and triangular (v3) flow coefficients of π±, K±, p+ overline{mathrm{p}} , {mathrm{K}}_{mathrm{S}}^0 , and Λ+ overline{Lambda} obtained with the scalar product method in Xe-Xe collisions at sqrt{s_{mathrm{NN}}} = 5.44 TeV are presented. The results are obtained in the rapidity range |y| < 0.5 and reported as a function of transverse momentum, pT, for several collision centrality classes. The flow coefficients exhibit a particle mass dependence for pT< 3 GeV/c, while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3 < pT< 8 GeV/c). The magnitude of the baryon v2 is larger than that of mesons up to pT = 6 GeV/c. The centrality dependence of the shape evolution of the pT-differential v2 is studied for the various hadron species. The v2 coefficients of π±, K±, and p+ overline{mathrm{p}} are reproduced by MUSIC hydrodynamic calculations coupled to a hadronic cascade model (UrQMD) for pT< 1 GeV/c. A comparison with vn measurements in the corresponding centrality intervals in Pb-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV yields an enhanced v2 in central collisions and diminished value in semicentral collisions.
Highlights
The flow coefficients exhibit a particle mass dependence for pT < 3 GeV/c, while a grouping according to particle type is found at intermediate transverse momenta (3 < pT < 8 GeV/c)
The measured v2 of all particle species, being mainly driven by the collision geometry, increases strongly with decreasing centrality up to the 40–50% centrality interval. This evolution is expected since v2 scales approximately linearly with the eccentricity of the overlap zone of the colliding nuclei [10]
The evolution of v2 with pT and centrality is similar to that reported in Pb-Pb collisions [30,31,32]
Summary
The flow coefficients exhibit a particle mass dependence for pT < 3 GeV/c, while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3 < pT < 8 GeV/c). The vn coefficients of unidentified charged particles have been measured in Xe-Xe collisions at the center-of-mass energy per nucleon pair These measurements further constrain the transport coefficients of the medium, such as η/s and bulk viscosity to entropy density ratio (ζ/s), and initial state models. For pT 3 GeV/c, the characteristic mass ordering (i.e., lighter particles having a larger vn than that of heavier particles at fixed pT), which arises from the interplay between radial flow (isotropic expansion) and anisotropic flow [28, 29], is described by hydrodynamic calculations [30,31,32,33,34] This mass ordering provides constraints on both η/s and ζ/s as the magnitude of vn depends on η/s, while the mass ordering is affected by ζ/s through its influence on radial flow. At intermediate pT, 3 < pT < 8 GeV/c, a grouping of vn of mesons and baryons is observed, with the flow of baryons being larger than that of mesons [32, 35,36,37]
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