Abstract
Measurements of the charged hadron multiplicity and transverse energy are presented for minimum bias PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair. The number of charged hadrons was obtained by two different methods based on the silicon pixel system of the CMS detector at the LHC. The two methods are in excellent agreement, resulting a charged hadron density of 1612 ± 55 for the 5% most central collisions. For the transverse energy measurement, CMS has almost Hermetic calorimetry coverage with fine granularity and excellent resolution. In addition, for particles near central rapidity, momenta from the tracker can be combined with the calorimeter data to give a significant improvement of the system resolution. A transverse energy density of 2.1 TeV is observed for the most central 2.5% collisions. The measurements are compared with heavy-ion results from earlier experiments, where a smooth dependence on the collision energy and impact parameter is observed.
Highlights
Quantum Chromodynamics predicts a phase transition at high temperature between hadronic and deconfined matter [1]
Measurements of the charged hadron multiplicity and transverse energy are presented for minimum bias PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair
The multiplicity of primary charged hadrons is measured by the pseudorapidity density, dNch/dη, where the pseudorapidity η = − ln[tan(θ/2)] and θ is the polar angle with respect to the beam line
Summary
Quantum Chromodynamics predicts a phase transition at high temperature between hadronic and deconfined matter [1]. Measurements of the charged hadron multiplicity and transverse energy are presented for minimum bias PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair. The number of charged hadrons was obtained by two different methods based on the silicon pixel system of the CMS detector at the LHC. The two methods are in excellent agreement, resulting a charged hadron density of 1612 ± 55 for the 5% most central collisions.
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