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

Abstract

This article discusses an estimation of the energy loss of partons in QGP in various collision systems using PHENIX data. We study the energy loss by two different methods, the fractional momentum losses $S_{\rm loss}=(p_{\rm T}^{\rm pp}-p_{\rm T}^{\rm AA})/p_{\rm T}^{\rm pp}$ and $S'_{\rm loss}=(p_{\rm T}^{\rm AA,in}-p_{\rm T}^{\rm AA,out})/p_{\rm T}^{\rm AA,in}$. $S_{\rm loss}$ is obtained by comparing the inclusive $p_{\rm T}$ spectra in the AA and pp collisions. In contrast, $S'_{\rm loss}$ is obtained by comparing in-plane and out-of-plane spectra using azimuthal anisotropy $v_{2}$. These quantities are extracted from the data in AuAu, CuAu, and CuCu collisions at $\sqrt{s_{\rm NN}} = 200$ GeV for $\pi^0$s, and the AuAu collisions at $\sqrt{s_{\rm NN}} = 200$ GeV for charged hadrons. The results show that $S_{\rm loss}$ is almost constant for a given centrality and does not depend on $p_{\rm T}$. In addition, $S_{\rm loss}$ is proportional to the squared path-length of the parton in the reaction area. In contrast, the results show that $S'_{\rm loss}$ slightly decreases up to $p_{\rm T}\sim 6$ GeV and is almost constant at higher $p_{\rm T}$ for a given centrality class. In addition, unlike $S_{\rm loss}$, $S'_{\rm loss}$ is not proportional to the difference of squared path-length in-plane and out-of-plane in the reaction area.