Thursday, April 4, 2013

1304.0899 (Roberto Preghenella for the ALICE Collaboration)

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

Roberto Preghenella for the ALICE Collaboration
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-$p_{\rm T}$.
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