Medium effect on the nuclear modification factor of protons and pions in intermediate-energy heavy ion collisions

Nuclear modification factors R-cp of protons and pions are investigated by simulating Au+Au collisions from 0.8A to 1.8A GeV in a framework of an isospin-dependent quantum molecular dynamics (IQMD) model. The Rcp of protons rise with an increase in the transverse particle momentum pT at different beam energies owing to radial flow and the multiple-collision effect. The rate of increase of Rcp is suppressed at higher beam energies. While the Rcp of pions display weaker pT dependence. By changing the in-medium nucleon-nucleon cross section, the Rcp of protons change a lot, while the Rcp of pions do not. In addition, by deactivating the N Delta -> NN and pi N -> Delta channels, the Rcp of protons change slightly in their increasing rates compared with the "original" case (with these two channels). However, the Rcp of pions is shifted down for the "no N Delta -> NN" case and has an inverse trend for the "no pi N -> Delta" case. Based on these observations, we argue that the observable Rcp is a suitable tool to better distinguish in-medium effects of protons and pions.