Bulk Properties of Pb-Pb collisions at sqrt(sNN) = 2.76 TeV measured by ALICE

TL;DR

This paper reports measurements of charged particle multiplicity and transverse energy in Pb-Pb collisions at 2.76 TeV, comparing results with lower-energy experiments and models, and discusses the centrality determination and Glauber model validity at high energies.

Contribution

It provides new measurements of global variables in Pb-Pb collisions at LHC energies and evaluates the applicability of the Glauber model at these energies.

Findings

Charged particle multiplicity and transverse energy measured as functions of centrality.

Comparison of results with lower-energy heavy-ion collision data.

Assessment of Glauber model validity at unprecedented collision energies.

Abstract

Global variables, such as the charged particle multiplicity and the transverse energy are important observables to characterize Relativistic Heavy Ion collisions and to constrain model calculations. The charged particle multiplicity dNch/deta and transverse energy dET/deta are measured at sqrt(sNN) = 2.76 TeV in Pb-Pb collisions as a function of centrality and in pp collisions. The fraction of inelastic cross section seen by the ALICE detector is calculated either using a Glauber model or the data corrected by simulations of nuclear and electromagnetic processes, or data collected with a minimum bias interaction trigger. The centrality, defined by the number of nucleons participating in the collision, is obtained, via the Glauber model, by relating the multiplicity distributions of various detectors in the ALICE Central Barrel and their correlation with the spectator energy measured by the Zero-Degree Calorimeters. The results are compared to corresponding results obtained at the significantly lower energies of the BNL AGS, the CERN SPS, and the BNL RHIC, and with models based on different mechanisms for particle production in nuclear collisions. Particular emphasis will be given to a discussion on systematic studies of the dependence of the centrality determination on the details of the Glauber model, and the validity of the Glauber model at unprecedented collision energies.