Ligth-flavour identified charged-hadron production in pp and Pb-Pb collisions at the LHC

TL;DR

This paper reports on measurements of light-flavour charged-hadron production in proton-proton and lead-lead collisions at the LHC, providing insights into the properties of the hot medium created and the mechanisms of particle production.

Contribution

It presents new transverse momentum spectra and yields for identified particles in pp and Pb-Pb collisions at multiple energies, with comparisons to models and previous experiments.

Findings

Pb-Pb collisions show the highest radial flow observed so far.

An unexpectedly low p/π ratio in Pb-Pb collisions.

High-$p_T$ nuclear modification factor is identical across particle species.

Abstract

Thanks to the unique detector design adopted to fulfill tracking and particle-identification (PID) requirements (e.g. low momentum cut-off and low material budget), the ALICE experiment provides significant information about hadron production both in pp and Pb-Pb collisions. In particular, the $p_{\rm T}$-differential and integrated production yields of identified particles play a key role in the study of the collective and thermal properties of the matter formed in high-energy heavy-ion collisions. Furthermore, the production of high-$p_{\rm T}$ particles provides insights into the property of the hot medium created in such collisions and the in-medium energy-loss mechanisms. Transverse momentum spectra of $\pi^{\pm}$, K$^{\pm}$, p and $\bar{\rm p}$ are measured at mid-rapidity ($\left|y\right| <~0.5$) over a wide momentum range, from $\sim$~100 MeV/$c$ up to $\sim$~20 GeV/$c$. The current results on light-flavour charged-hadron production will be presented for pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV and for Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV. Integrated production yields, transverse momentum spectra and particle ratios in pp are discussed as a function of the collision energy and compared to previous experiments and commonly-used Monte Carlo models. Pb-Pb collisions at the LHC feature the highest radial flow ever observed and an unexpectedly low p/$\pi$ production ratio. The results are presented as a function of collision centrality and compared to RHIC data in Au-Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV and predictions from thermal and hydrodynamic models. The nuclear modification factor ($R_{\rm AA}$) of identified hadrons will also be discussed and compared to unidentified charged particles and theoretical predictions. This is observed to be identical for all particle species at high-$p_{\rm T}$.