Abstract
The first measurement of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair is presented. For an event sample corresponding to the most central 5% of the hadronic cross section, the pseudorapidity density of primary charged particles at midrapidity is , which corresponds to per participating nucleon pair. This represents an increase of about a factor 1.9 relative to collisions at similar collision energies, and about a factor 2.2 to central Au-Au collisions at . This measurement provides the first experimental constraint for models of nucleus-nucleus collisions at LHC energies.
- Received 19 November 2010
DOI:https://doi.org/10.1103/PhysRevLett.105.252301
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© 2010 CERN, for the ALICE Collaboration