Considerations on the suppression of charged particles and $\ddot{I}{€}^0$ in high energy heavy ion collisions

Abstract

Experimental results related to charged particle and $\ddot{I}{€}^0$ suppression obtained at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven for Au-Au (Cu-Cu) collisions and at the Large Hadron Collider (LHC) at CERN for Pb-Pb (Xe-Xe) collisions are compiled in terms of the usual nuclear modification factors, $R_{AA}$ and $R_{CP}$, and of the newly introduced $R_{AA}^N$ and $R_{CP}^N$ as a function of $⟨N_{part}⟩$ and $⟨d{N}_{ch}/d\hat{I}\cdot ⟩$. The studies are focused on a $p_T$ range in the region of maximum suppression evidenced in the experiments. The core contribution to $R_{AA}$ is presented. Considerations on the missing suppression in high charged particle multiplicity events for pp collisions at 7 TeV are presented. The trends of $R_{CP}$ and $R_{CP}^N$ for charged particles and $R_{AA}^{\ddot{I}{€}^0}$ and $(R_{AA}^N{)}^{\ddot{I}{€}^0}$ as a function of $\sqrt{s_{NN}}$, measured at RHIC in Au-Au collisions and at LHC in Pb-Pb collisions, show a suppression that becomes larger from $\sqrt{s_{NN}}$ = 39 GeV up to $\sqrt{s_{NN}}$=200 GeV, followed by a saturation up to the highest energy of $\sqrt{s_{NN}}$ =5.02 TeV in Pb-Pb collisions. A clear change in the dependence of $(1-R_{AA}^{\ddot{I}{€}^0})/⟨dN/dy⟩$ for the most central collisions as a function of collision energy is evidenced in the region of $\sqrt{s_{NN}}$ =62.4 - 130 GeV.

ICHEP 2020