Charged Hadron Nuclear Modification Factors in the Beam Energy Scan Data from STAR

Abstract

Suppression of high transverse momentum (pT ) charged hadrons can be measured by the nuclear modification factor, which compares binary collision scaled pT spectra from central heavy-ion collisions to a reference, either proton-proton (RAA) or peripheral heavy-ion collisions (RCP) by taking their ratio. At high sNN the nuclear modification factor at high pT is observed to be suppressed, i.e. less than unity. The complex array of processes that can modify particle spectra in nuclear collisions span cold nuclear matter effects, a strongly interacting medium, and an extended phase of hadronic re-scatterings. RHIC’s broad range of collision systems and energies combined with model comparisons provide the tools to investigate the beam energy dependence of nuclear modification factors and help to disentangle the spectral modifications that are due to each of these contributions. Measurements of charged hadron RCP( sNN , pT) for sNN = 7.7 200GeV show a smooth transition from strong enhancement of high pT charged hadrons at low energies to strong suppression at high energies. AMPT and HIJING failed to reproduce the results from data. Further tuning of the models may yet facilitate the investigation of the relative contributions from jet quenching and Cronin enhancement.