Pion, kaon, and proton production in central Pb-Pb Collisions at $\sqrt{s_{NN}} = 2.76$ TeV

TL;DR

This paper reports on the measurement of pion, kaon, and proton production in central Pb-Pb collisions at 2.76 TeV, revealing increased radial flow and a discrepancy in proton-to-pion ratios compared to thermal model predictions.

Contribution

First measurement of identified particle spectra at LHC energies in central Pb-Pb collisions, highlighting increased radial flow and deviations from thermal model expectations.

Findings

Radial flow velocity increases with collision energy.

K/π ratio aligns with thermal model predictions.

p/π ratio is lower than thermal model expectations by a factor of 1.5.

Abstract

In this Letter we report the first results on $\pi^\pm$, K$^\pm$, p and $\mathrm {p\overline{p}}$ production at mid-rapidity ($\left|y\right|<0.5$) in central Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, measured by the ALICE experiment at the LHC. The $p_{\rm T}$ distributions and yields are compared to previous results at $\sqrt{s_{\rm NN}}$ = 200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with $\sqrt{s_{\rm NN}}$, which in hydrodynamic models is expected as a consequence of the increasing particle density. While the ${\rm K}/\pi$ ratio is in line with predictions from the thermal model, the ${\rm p}/\pi$ ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.