Suppression of charged particle production at large transverse momentum in central Pb–Pb collisions at

Inclusive transverse momentum spectra of primary charged particles in Pb–Pb collisions at s NN = 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| | η | 0.8 and 0.3 T 0.3 p T 20 GeV / c are compared to the expectation in pp collisions at the same s NN , scaled by the number of underlying nucleon–nucleon collisions. The comparison is expressed in terms of the nuclear modification factor R AA R AA . The result indicates only weak medium effects (R AA ≈0.7) ( R AA ≈ 0.7 ) in peripheral collisions. In central collisions, R AA R AA reaches a minimum of about 0.14 at p T =6–7 GeV/c p T = 6 – 7 GeV / c and increases significantly at larger p T p T . The measured suppression of high- p T p T 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.