Systematic study of energy loss in the quark-gluon plasma at RHIC-PHENIX

systems using PHENIX data. We study the energy loss by two different methods, the fractional momentum losses Sloss = (p T − pAA T )/p pp T and S ′ loss = (p AA,in T − p AA,out T )/p AA,in T . Sloss is obtained by comparing the inclusive pT spectra in the AA and pp collisions. In contrast, S′ loss is obtained by comparing in-plane and out-of-plane spectra using azimuthal anisotropy v2. These quantities are extracted from the data in AuAu, CuAu, and CuCu collisions at sNN = 200 GeV for π0s, and the AuAu collisions at sNN = 200 GeV for charged hadrons. The results show that Sloss is almost constant for a given centrality and does not depend on pT. In addition, Sloss is proportional to the squared path-length of the parton in the reaction area. In contrast, the results show that S′ loss slightly decreases up to pT ∼ 6 GeV and is almost constant at higher pT for a given centrality class. In addition, unlike Sloss, S′ loss is not proportional to the difference of squared path-length in-plane and out-of-plane in the reaction area.