Seventh and eighth-order cumulants of net-proton multiplicity distributions in heavy-ion collisions at RHIC-STAR

Abstract

We report the first measurements of seventh and eighth-order cumulants of net-proton distributions in Au+Au collisions at √SNN=27,54.4, and 200 GeV. The measurements are performed at mid-rapidity |y| < 0.5 within 0.4 < pT < 2.0 GeV/c using the Time Projection Chamber and Time-of-Flight detector. Motivation for the measurements comes from lattice-QCD and QCD based model calculations that predict their negative signs for a crossover quark-hadron transition. While 0-40% centrality measurements at √SNN=54.4 and 200 GeV are consistent with zero within large uncertainties, at √SNN=27 GeV, they are negative with ≤ 1.4σ significance. The peripheral 70-80% measurements are either positive or consistent with zero for the three energies.