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

Abstract

Inclusive transverse momentum spectra of primary charged particles in Pb–Pb collisions at $\sqrt{s_{NN}} = 2.76 \text{ TeV}$ 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 $|\eta| < 0.8$ and $0.3 < p_T < 20 \text{ GeV}/c$ are compared to the expectation in pp collisions at the same $\sqrt{s_{NN}}$, scaled by the number of underlying nucleon–nucleon collisions. The comparison is expressed in terms of the nuclear modification factor $R_{AA}$. The result indicates only weak medium effects ($R_{AA} \approx 0.7$) in peripheral collisions. In central collisions, $R_{AA}$ reaches a minimum of about 0.14 at $p_T = 6\text{--}7 \text{ GeV}/c$ and increases significantly at larger $p_T$. The measured suppression of high-$p_T$ 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.