Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at sqrt(sNN) = 2.76 TeV

Inclusive transverse momentum spectra of primary charged particles in Pb–Pb collisions at √sNN= 2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented for central and peripheral collisions, corresponding to 0–5% and 70–80% of the hadronic Pb–Pb cross section. The measured charged particle spectra in |η | <0.8 and 0.3 <pT <20 GeV/c are compared to the expectation in pp collisions at the same √sNN , scaled by the number of underlying nucleon–nucleon collisions. The comparison is expressed in terms of the nuclear modification factor RAA. The result indicates only weak medium effects (RAA ≈ 0.7) in peripheral collisions. In central collisions, RAA reaches a minimum of about 0.14 at pT = 6–7 GeV/c and increases significantly at larger pT . The measured suppression of high–pT particles is stronger than that observed at lower collision energies, indicating that a very dense medium is formed in central Pb–Pb collisions at the LHC