Measurement of the pseudorapidity and centrality dependence of the transverse energy density in PbPb collisions at sqrt(s[NN]) = 2.76 TeV

TL;DR

This study measures the transverse energy density in PbPb collisions at 2.76 TeV, revealing that energy per particle increases with collision energy and centrality, with energy densities far exceeding normal nuclear matter.

Contribution

First measurement of pseudorapidity and centrality dependence of transverse energy density in PbPb collisions at 2.76 TeV using CMS at the LHC.

Findings

Transverse energy density increases faster than charged particle multiplicity with energy.

Energy density at 1 fm/c is about 14 GeV/fm^3, 100 times nuclear matter density.

Energy density is higher than at RHIC at 200 GeV.

Abstract

The transverse energy ET in PbPb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy sqrt(s[NN]) has been measured over a broad range of pseudorapidity eta and collision centrality using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity d(ET)/d(eta) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse energy per unit pseudorapidity in peripheral to central collisions varies significantly as the pseudorapidity increases from eta = 0 to abs(eta) = 5.0. For the 5% most central collisions the energy density per unit volume is estimated to be about 14 GeV/fm^3 at a time of 1 fm/c after the collision. This is about 100 times larger than normal nuclear matter density and a factor of 2.6 times higher than the energy density reported at sqrt(s[NN]) = 200 GeV at RHIC.