Charged particle production in Pb-Pb collisions at the LHC with the ALICE detector

Floris, M. and Abelev, B. and Adam, J. and Adamová, D. and Adare, A. M. and Aggarwal, M. M. and Agnello, M. and Agócs, András and Agostinelli, A. and Ahammed, Z. and Ahmad, Masoodi A. and Ahmad, N. and Ahn, S. A. and Ahn, S. U. and Ajaz, M. and Akindinov, A. and Alaniz, E. C. and Aleksandrov, D. and Alessandro, B. and Alici, A. and Alkin, A. and Alme, J. and Alt, T. and Altini, V. and Altinpinar, S. and Altsybeev, I. and Andrei, C. and Andronic, A. and Anguelov, V. and Anielski, J. and Barnaföldi, Gergely Gábor and Bencédi, Gyula and Berényi, Dániel and Boldizsár, László and Dénes, Ervin and Hamar, Gergő and Lévai, Péter and Pochybova, Sona (2013) Charged particle production in Pb-Pb collisions at the LHC with the ALICE detector. NUCLEAR PHYSICS A, 910-91. pp. 343-346. ISSN 0375-9474

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Abstract

The ALICE collaboration measured charged particle production in √ sNN = 2.76 TeV Pb–Pb collisions at the LHC. We report on results on charged particle multiplicity and transverse momentum spectra. All the results are presented as a function of the centrality of the collision, estimated with a Glauber Monte Carlo fit to multiplicity distributions reconstructed in various detectors. The applicability of the Glauber model at LHC energies, the precision of the centrality determination and the related systematic uncertainties are discussed in detail. Particles are tracked in the pseudorapidity window |η| . 0.9 with the silicon Inner Tracking System (ITS) and the Time Projection Chamber (TPC), over the range 0.15 < pT . 50 GeV/c. The low-pT cut-off is further reduced in the multiplicity measurement using “tracklets”, reconstructed in the 2 innermost layers of the ITS. The charged particle multiplicity is measured in |η| < 0.5 to be dNch/dη = 1601 ± 60 in 5% most central Pb–Pb collisions, indicating an energy density a factor ∼ 3 higher than at RHIC. Its evolution with centrality shows a pattern strikingly similar to the one measured at RHIC. Intermediate (5 . pT . 15 GeV/c) transverse momentum particles are found to be most strongly suppressed with respect to pp collisions, consistent with a large energy loss of hardscattered partons in the hot and dense medium. The results are presented in terms of the nuclear modification factor RAA and compared to theoretical expectations.

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