Measurements of the fractional momentum loss ($S_{rm loss}equiv{delta}p_T/p_T$) of high-transverse-momentum-identified hadrons in heavy ion collisions are presented. Using $pi^0$ in Au$+$Au and Cu$+$Cu collisions at $sqrt{s_{_{NN}}}=62.4$ and 200 GeV measured by the PHENIX experiment at the Relativistic Heavy Ion Collider and and charged hadrons in Pb$+$Pb collisions measured by the ALICE experiment at the Large Hadron Collider, we studied the scaling properties of $S_{rm loss}$ as a function of a number of variables: the number of participants, $N_{rm part}$, the number of quark participants, $N_{rm qp}$, the charged-particle density, $dN_{rm ch}/deta$, and the Bjorken energy density times the equilibration time, $varepsilon_{rm Bj}tau_{0}$. We find that the $p_T$ where $S_{rm loss}$ has its maximum, varies both with centrality and collision energy. Above the maximum, $S_{rm loss}$ tends to follow a power-law function with all four scaling variables. The data at $sqrt{s_{_{NN}}}$=200 GeV and 2.76 TeV, for sufficiently high particle densities, have a common scaling of $S_{rm loss}$ with $dN_{rm ch}/deta$ and $varepsilon_{rm Bj}tau_{0}$, lending insight on the physics of parton energy loss.
Download