Considerations on the suppression of charged particles and $\pi^0$ in high energy heavy ion collisions

TL;DR

This paper compiles and analyzes experimental data on charged particle and $$ suppression in high-energy heavy ion collisions at RHIC and LHC, introducing new nuclear modification factors and examining suppression trends across energies.

Contribution

It introduces new nuclear modification factors $R^{N}_{AA}$ and $R^{N}_{CP}$, and provides a comprehensive analysis of suppression patterns across different collision energies and systems.

Findings

Suppression increases from 39 GeV to 200 GeV, then saturates up to 5.02 TeV.

A change in suppression dependence occurs around 62.4-130 GeV.

Missing suppression in high multiplicity pp collisions at 7 TeV is discussed.

Abstract

Experimental results related to charged particle and $\pi^{0}$ 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 $R^{N}_{AA}$ and $R^{N}_{CP}$ as a function of $\langle N_{part} \rangle$ and $\langle dN_{ch}/d\eta\rangle$. 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 $R^N_{CP}$ for charged particles and $R_{AA}^{\pi^0}$ and $(R_{AA}^N)^{\pi^0}$ 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 $(1-R_{AA}^{\pi^0})/\langle dN/dy \rangle$ for the most central collisions as a function of collision energy is evidenced in the region of $\sqrt{s_{NN}}$ =62.4 - 130 GeV.