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

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

Azimuthal anisotropy of charged particles from multiparticle correlations in pPb and PbPb collisions with CMS

“…The first attempts to address this question in pPb collisions were presented in Ref. [16] by directly measuring four-particle azimuthal correlations, where the elliptic flow signal (v 2 ) was obtained in the context of hydrodynamic models using the cumulant method.…”

“…The ratios from PbPb collisions are also shown for completeness. The v 2 {2} and v 2 {4} data are taken from previously published CMS results [16]. The solid curves correspond to theoretical predictions based on hydrodynamics with initial-state geometry fluctuations.…”

Flow and correlation phenomena measurements in pp, pPb and PbPb collisions at CMS

“…The contribution to v n coefficients from back-to-back jet correlations are corrected by subtracting correlations from very low-multiplicity events (v sub n ), as done in Refs. [4,13] Results from symmetric cumulants allow to further study the correlations of different v n coefficients. The measurements of SC(2, 3) and SC(2, 4), for 0.3 < p T < 3 GeV/c from four-particle correlations, are shown in In Fig.…”

Collective effects in light–heavy ion collisions

“…We compare to experimental data from the CMS collaboration [10]. We then present predictions for the systematics of the transverse momentum dependent anisotropy coefficients v n (p T ) in p+Au, d+Au, and 3 He+Au collisions at top RHIC energies.…”