Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}} = 2.76$ TeV

TL;DR

This study measures how the production of charged particles at high transverse momentum varies with collision centrality in Pb-Pb collisions at 2.76 TeV, revealing strong suppression in central collisions and a rise at higher momenta.

Contribution

It provides detailed measurements of the nuclear modification factor across different centralities and high transverse momenta, enhancing understanding of parton energy loss in quark-gluon plasma.

Findings

High-$p_T$ particle suppression is strongest in central collisions.

The nuclear modification factor rises above 7 GeV/$c$ in central collisions.

Suppression is weaker and nearly constant in peripheral collisions.

Abstract

The inclusive transverse momentum ($p_{\rm T}$) distributions of primary charged particles are measured in the pseudo-rapidity range $|\eta|<0.8$ as a function of event centrality in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$ TeV with ALICE at the LHC. The data are presented in the $p_{\rm T}$ range $0.15<p_{\rm T}<50$ GeV/$c$ for nine centrality intervals from 70-80% to 0-5%. The Pb-Pb spectra are presented in terms of the nuclear modification factor $R_{\rm{AA}}$ using a pp reference spectrum measured at the same collision energy. We observe that the suppression of high-$p_{\rm T}$ particles strongly depends on event centrality. In central collisions (0-5%) the yield is most suppressed with $R_{\rm{AA}}\approx0.13$ at $p_{\rm T}=6$-7 GeV/$c$. Above $p_{\rm T}=7$ GeV/$c$, there is a significant rise in the nuclear modification factor, which reaches $R_{\rm{AA}} \approx0.4$ for $p_{\rm T}>30$ GeV/$c$. In peripheral collisions (70-80%), the suppression is weaker with $R_{\rm{AA}} \approx 0.7$ almost independently of $p_{\rm T}$. The measured nuclear modification factors are compared to other measurements and model calculations.