2022/07/20 by STAR Collaboration, Aboona, B. E., Adam, J. +357 · 1 citation
#FOS: Physical sciences #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.2207.09837
We report the beam energy and collision centrality dependence of fifth and sixth order cumulants (C5, C6) and factorial cumulants (κ5, κ6) of net-proton and proton distributions, from √sNN = 3 - 200 GeV Au+Au collisions at RHIC. The net-proton cumulant ratios generally follow the hierarchy expected from QCD thermodynamics, except for the case of collisions at √sNN = 3 GeV. C6/C2 for 0-40% centrality collisions is increasingly negative with decreasing √sNN, while it is positive for the lowest √sNN studied. These observed negative signs are consistent with QCD calculations (at baryon chemical potential, μB ≤ 110 MeV) that include a crossover quark-hadron transition. In addition, for √sNN ≥ 11.5 GeV, the measured proton κn, within uncertainties, does not support the two-component shape of proton distributions that would be expected from a first-order phase transition. Taken in combination, the hyper-order proton number fluctuations suggest that the structure of QCD matter at high baryon density, μB∼ 750 MeV (√sNN = 3 GeV) is starkly different from those at vanishing μB∼ 20MeV (√sNN = 200 GeV and higher).