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.
Highlights
Measurements of dihadron correlations are a well established technique for studying the properties of particle production in the high density medium created in heavy ion collisions
(2 < | η| < 4) dihadron correlations in PbPb collisions at Large Hadron Collider (LHC) energies, as well as the relationship between these two-particle correlations and single-particle angular distributions. These results provide extensive input to the interpretation of these observables in terms of broad theoretical concepts such as hydrodynamic flow and quantitative models of particle production and propagation in the highdensity medium
CentralAs was seen previously for central PbPb collisions, the associated yields differ significantly from those observed in pp interactions
Summary
Measurements of dihadron correlations are a well established technique for studying the properties of particle production in the high density medium created in heavy ion collisions. The potential connection between the extracted Fourier coefficients from the correlation data and the azimuthal anisotropy harmonics for single particles is investigated This measurement provides a comprehensive examination of the centrality and transverse momentum (1 < pT < 20 GeV/c) dependencies of the short-range (| η| < 1) and long-range (2 < | η| < 4) dihadron correlations in PbPb collisions at LHC energies, as well as the relationship between these two-particle correlations and single-particle angular distributions. These results provide extensive input to the interpretation of these observables in terms of broad theoretical concepts such as hydrodynamic flow and quantitative models of particle production and propagation in the highdensity medium. The detector, the event selection and the extraction of the correlation functions are described in Sects. 2 and 3, while the extracted results are described in Sects. 4 and 5
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