Centrality dependence of the nuclear modification factor of charged pions, kaons, and protons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV

TL;DR

This paper measures the transverse momentum spectra of pions, kaons, and protons in Pb-Pb collisions at 2.76 TeV, analyzing how their nuclear modification factors depend on collision centrality and particle type.

Contribution

It provides detailed measurements of identified particle spectra and nuclear modification factors across a wide pT range in Pb-Pb collisions, highlighting the particle species independence at high pT.

Findings

Nuclear modification factors are similar for all three particle species above 10 GeV/c.

Proton-to-pion and kaon-to-pion ratios peak at 3 GeV/c in central collisions.

Data constrains models of the transition from soft to hard physics.

Abstract

Transverse momentum ($p_{\rm{T}}$) spectra of pions, kaons, and protons up to $p_{\rm{T}} = 20$ GeV/$c$ have been measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV using the ALICE detector for six different centrality classes covering 0-80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at $p_{\rm{T}} \approx 3$ GeV/$c$ in central Pb-Pb collisions that decreases towards more peripheral collisions. For $p_{\rm{T}} > 10$ GeV/$c$, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within systematic uncertainties of 10-20%. This suggests there is no direct interplay between the energy loss in the medium and the particle species composition in the hard core of the quenched jet. For $p_{\rm{T}} < 10$ GeV/$c$, the data provide important constraints for models aimed at describing the transition from soft to hard physics.