Energy dependence of moments of net-proton and net-charge multiplicity distributions at STAR

Abstract

We present the energy dependence of moments of net-proton and net-charge multiplicity distributions in Au+Au collisions measured by the STAR experiment in the first phase of the Beam Energy Scan (BES) at the Relativistic Heavy Ion Collider (RHIC). By using the time of flight detector for particle identification, the upper transverse momentum (pT) limit for proton and anti-proton is extended from 0.8 GeV/c up to 2 GeV/c. The pT and rapidity acceptance dependence study for the moments of net-proton distribution show that the larger the acceptance is, the greater the deviation from unity. The most pronounced structure is found in the energy dependence of κσ2 of net-proton distributions from the 0 ∼ 5% most central collisions within 0.4 < pT < 2 GeV/c and at mid-rapidity |y| < 0.5. At energies above 39 GeV, the values of κσ2 are close to unity and for energies below 39 GeV, it shows significant deviation below unity around 19.6 and 27 GeV, then a large increase above unity is observed at 7.7 GeV.