Multiplicity and transverse-momentum dependence of two- and four-particle correlations in pPb and PbPb collisions

TL;DR

This paper investigates two- and four-particle correlations in pPb and PbPb collisions at the LHC, revealing similar anisotropic flow patterns and comparing experimental results with theoretical models like color glass condensate and hydrodynamics.

Contribution

It provides the first detailed comparison of multi-particle correlations between pPb and PbPb collisions across a wide multiplicity range.

Findings

Similar v[3] signals in pPb and PbPb systems.

Correlated yields and anisotropy harmonics increase with multiplicity.

Experimental results are consistent with both CGC and hydrodynamic model predictions.

Abstract

Measurements of two- and four-particle angular correlations for charged particles emitted in pPb collisions are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding to an integrated luminosity of approximately 31 inverse nanobarns, were collected during the 2013 LHC pPb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV by the CMS experiment. The results are compared to 2.76 TeV semi-peripheral PbPb collision data, collected during the 2011 PbPb run, covering a similar range of particle multiplicities. The observed correlations are characterized by the near-side (abs(Delta(phi)~0) associated pair yields and the azimuthal anisotropy Fourier harmonics (v[n]). The second-order (v[2]) and third-order (v[3]) anisotropy harmonics are extracted using the two-particle azimuthal correlation technique. A four-particle correlation method is also applied to obtain the value of v[2] and further explore the multi-particle nature of the correlations. Both associated pair yields and anisotropy harmonics are studied as a function of particle multiplicity and transverse momentum. The associated pair yields, the four-particle v[2], and the v[3] become apparent at about the same multiplicity. A remarkable similarity in the v[3] signal as a function of multiplicity is observed between the pPb and PbPb systems. Predictions based on the color glass condensate and hydrodynamic models are compared to the experimental results.