High pT single identified particles in various systems, various collision energies, and several scaling variables

Results of the opacity of a system created in heavy ion collisions are presented. This property of the system can be described through measurements of the fractional energy loss of single identified hadrons at high p T and allows to establish scaling properties based on scaling variables such as number of participants, number of quark participants, charged particle density, and Bjorken energy density. To characterize the energy loss mechanism an extended study is shown with data-sets both from PHENIX at RHIC and ALICE at LHC and by plotting the fractional momentum loss against several scaling variables. It is shown that in the p T region where hard scattering is expected to dominate, in all but the most peripheral collisions, δ p T / p T exhibits a simple scaling with those global observables.