Centrality dependence of $\rm \mathbf \pi$, K, p production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

TL;DR

This paper reports on the measurement of pion, kaon, and proton production in Pb-Pb collisions at 2.76 TeV, revealing stronger radial flow in central collisions and discrepancies with hydrodynamic models in peripheral collisions.

Contribution

It provides detailed transverse momentum spectra and yield ratios across different centralities, highlighting the limitations of existing hydrodynamic models at LHC energies.

Findings

Stronger radial flow observed in central collisions.

Peripheral collision spectra not well described by hydrodynamics.

Proton-to-pion yield ratio lower than thermal model predictions.

Abstract

In this paper measurements are presented of $\rm \pi$$^+$, $\rm \pi$$^-$, K$^+$, K$^-$, p and $\overline{\rm p}$ production at mid-rapidity < 0.5, in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV as a function of centrality. The measurement covers the transverse momentum ($p_{\rm T}$) range from 100, 200, 300 MeV/$c$ up to 3, 3, 4.6 GeV/$c$, for $\rm\pi$, K, and p respectively. The measured $p_{\rm T}$ distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the $p_{\rm T}$ distributions are not well reproduced by hydrodynamic models. Ratios of integrated particle yields are found to be nearly independent of centrality. The yield of protons normalized to pions is a factor ~1.5 lower than the expectation from thermal models.