Long-range and short-range dihadron angular correlations in central PbPb collisions at a nucleon-nucleon center of mass energy of 2.76 TeV

TL;DR

This paper reports the first measurements of dihadron correlations in central PbPb collisions at 2.76 TeV, revealing a broadening of the away-side peak and the persistence of the ridge phenomenon over a wide pseudorapidity range, with dependencies on particle transverse momentum.

Contribution

It provides new experimental data on long-range and short-range dihadron correlations in heavy-ion collisions at LHC energies, highlighting the ridge phenomenon and azimuthal broadening effects.

Findings

Observation of azimuthal broadening in away-side correlations

Detection of the ridge phenomenon up to |Delta(eta)|=4

Dependence of the ridge strength on particle transverse momentum

Abstract

First measurements of dihadron correlations for charged particles are presented for central PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV over a broad range in relative pseudorapidity, Delta(eta), and the full range of relative azimuthal angle, Delta(phi). The data were collected with the CMS detector, at the LHC. A broadening of the away-side (Delta(phi) approximately pi) azimuthal correlation is observed at all Delta(eta), as compared to the measurements in pp collisions. Furthermore, long-range dihadron correlations in Delta(eta) are observed for particles with similar phi values. This phenomenon, also known as the "ridge", persists up to at least |Delta(eta)| = 4. For particles with transverse momenta (pt) of 2-4 GeV/c, the ridge is found to be most prominent when these particles are correlated with particles of pt = 2-6 GeV/c, and to be much reduced when paired with particles of pt = 10-12 GeV/c.