Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at sqrt(s[NN]) = 2.76 TeV

TL;DR

This paper presents detailed measurements of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at 2.76 TeV, revealing how jet-like and long-range structures vary with collision centrality and particle momentum.

Contribution

It provides a comprehensive analysis of dihadron correlations and azimuthal harmonics in heavy-ion collisions, including factorization properties and centrality dependence, using CMS data.

Findings

Jet peak enhancement with increasing centrality.

Long-range correlations factorize into single-particle anisotropies.

Azimuthal harmonics vary with particle momentum and centrality.

Abstract

Measurements from the CMS experiment at the LHC of dihadron correlations for charged particles produced in PbPb collisions at a nucleon-nucleon centre-of-mass energy of 2.76 TeV are presented. The results are reported as a function of the particle transverse momenta (pt) and collision centrality over a broad range in relative pseudorapidity [Delta(eta)] and the full range of relative azimuthal angle [Delta(phi)]. The observed two-dimensional correlation structure in Delta(eta) and Delta(phi) is characterised by a narrow peak at (Delta(eta), Delta(phi)) approximately (0, 0) from jet-like correlations and a long-range structure that persists up to at least |Delta(eta)| = 4. An enhancement of the magnitude of the short-range jet peak is observed with increasing centrality, especially for particles of pt around 1-2 GeV/c. The long-range azimuthal dihadron correlations are extensively studied using a Fourier decomposition analysis. The extracted Fourier coefficients are found to factorise into a product of single-particle azimuthal anisotropies up to pt approximately 3-3.5 GeV/c for at least one particle from each pair, except for the second-order harmonics in the most central PbPb events. Various orders of the single-particle azimuthal anisotropy harmonics are extracted for associated particle pt of 1-3 GeV/c, as a function of the trigger particle pt up to 20 GeV/c and over the full centrality range.