KRUGER2012 International Workshop on Discovery Physics at the LHC

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

3 Dec 2012, 14:30

30m

Protea Kruger Gate Hotel

Parallel Session II: Heavy Ion Collisions

Speaker

Dr Roberto Preghenella (Museo Storico della Fisica e Centro di Studi e Ricerche "Enrico Fermi" and INFN Sezione di Bologna)

Description

Thanks to the unique detector design adopted to fulfil 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 spectral shapes and 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_T particles provides insights into the density of the medium and the in-medium energy-loss mechanisms. Transverse momentum spectra of &pi^±, K^±, p and ¯p are measured at mid-rapidity (|y| < 0.5) over a wide momentum range, from ~100 MeV/c up to ~20 GeV/c. The measurements are performed exploiting the dE/dx in silicon (ITS) and gas (TPC), the time-of-flight (TOF) and the ring-imaging Cherenkov (HMPID) particle-identification techniques, which will be briefly reviewed in this report. The current results on light-flavour charged-hadron production will be presented for pp collisions at √s = 0.9, 2.76 and 7 TeV and for Pb--Pb collisions at √s_NN = 2.76 TeV. Production yields, spectral shapes 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 √s_NN = 200 GeV and predictions from thermal and hydrodynamic models. The nuclear modification factor (R_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_T.