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 (Delta eta) of the particle pair at small relative azimuthal angle (abs(Delta phi) < pi/3). The correlations are decomposed into a jet component that dominates the short-range correlations (abs(Delta eta) < 1), and a component that persists at large Delta eta 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 lab frame mid-rapidity value and are studied as a function of eta[cm]. The normalized v[2] distribution is found to be asymmetric about eta[cm] = 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.
Highlights
Studies of two-particle correlations play an important role in understanding the underlying mechanism of particle production in high-energy nuclear collisions [1,2,3]
A recent study suggests that anisotropic escape probabilities may already produce large final-state anisotropies without the need for significant rescattering [21]. Another possible mechanism proposed to account for the initial-state correlations is the color glass condensate (CGC), where the two-gluon density is enhanced at small φ over a wide η range [22,23]
The combinatorial background is assumed to be uniform in φ and normalized by the ZYAM
Summary
Studies of two-particle correlations play an important role in understanding the underlying mechanism of particle production in high-energy nuclear collisions [1,2,3] These correlations are studied in a two-dimensional φ- η space, where φ and η are the differences in the azimuthal angle φ and the pseudorapidity η of the two particles. A recent study suggests that anisotropic escape probabilities may already produce large final-state anisotropies without the need for significant rescattering [21] Another possible mechanism proposed to account for the initial-state correlations is the color glass condensate (CGC), where the two-gluon density is enhanced at small φ over a wide η range [22,23]. To reproduce the magnitude of the ridge in AA collisions, the CGC-based models require
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