Pseudorapidity dependence of long-range two-particle correlations in $pPb$ collisions at $\sqrt{s_{NN}}= 5.02$ TeV

Abstract

Two-particle correlations in $pPb$ collisions at a nucleon-nucleon center-of-mass energy of $5.02$TeV are studied as a function of the pseudorapidity separation ($Δη$) of the particle pair at small relative azimuthal angle ($|Δϕ|<\pi/3$). The correlations are decomposed into a jet component that dominates the short-range correlations ($|Δη|<1$), and a component that persists at large $Δη$ and may originate from collective behavior of the produced system. The events are classified in terms of the multiplicity of the produced particles. Finite azimuthal anisotropies are observed in high-multiplicity events. The second and third Fourier components of the particle-pair azimuthal correlations, $V_2$ and $V_3$, are extracted after subtraction of the jet component. The single-particle anisotropy parameters $v_2$ and $v_3$ are normalized by their laboratory frame midrapidity value and are studied as a function of $η_{c.m.}$. The normalized $v_2$ distribution is found to be asymmetric about $η_{c.m.}$=0, with smaller values observed at forward pseudorapidity, corresponding to the direction of the proton beam, while no significant pseudorapidity dependence is observed for the normalized $v_3$ distribution within the statistical uncertainties.