By comparing the results from various collision centralities, we found that the autocorrelation effects are not significant in the results with the collision centralities “refmult-3” and “refmult-2,” which use midrapidity charged particles but exclude (anti)protons and the analysis region, respectively. Furthermore, due to the contributions of spectator protons, we observed poor centrality resolution when using charged particles at forward η regions at low energies. Centrality resolutions are decreases towards peripheral collisions.

First report of complete second order cumulant matrix net-proton, net-charge, and net-kaon multiplicity distributions for the first phase of the beam energy scan program at the Relativistic Heavy Ion Collider.

We report the first measurements of the moments of net-kaon multiplicity distributions in Au+Au collisions at sNN=7.7 , 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV. Comparisons are made with Poisson and negative binomial baseline calculations as well as with UrQMD, a transport model (UrQMD) that does not include effects from the QCD critical point. Within current uncertainties, the net-kaon cumulant ratios appear to be monotonic as a function of collision energy.

We present the first estimates of isothermal compressibility ( kT ) of hadronic matter formed in relativistic nuclear collisions (sqrt{sNN}=7.7 GeV to 2.76 TeV) using experimentally observed multiplicity fluctuations. The results are compared with calculations from UrQMD, AMPT, and EPOS event generators, and estimations of kT are made for Pb–Pb collisions at the CERN Large Hadron Collider. A hadron resonance gas (HRG) model has been used to calculate kT as a function of collision energy. Our results show a decrease in kT at low collision energies to sNN∼20 GeV , beyond which the kT values remain almost constant.

The extreme temperatures and energy densities generated by ultra-relativistic collisions between heavy nuclei produce a state of matter with surprising fluid properties. We find that Lambda and anti-Lambda hyperons show a positive polarization of the order of a few percent, consistent with some hydrodynamic predictions. These data provide the first experimental access to the vortical structure of the ‘perfect fluid’ created in a heavy ion collision. They should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the Strong Force. Our results extend the recent discovery of hydrodynamic spin alignment to the subatomic realm.

A comprehensive study of the second order diagonal susceptibilities and cross correlations has been made within a thermal model approach of the hadron resonance gas model as well as with a hadronic transport model, ultra-relativistic quantum molecular dynamics. The transverse momentum cutoff dependence of suitably normalised susceptibilities are proposed as useful observables to probe the properties of the medium at freezeout.