Abstract

The second- and third-order azimuthal anisotropy Fourier harmonics of charged particles produced in pPb collisions, at $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV, are studied over a wide range of event multiplicities. Multiparticle correlations are used to isolate global properties stemming from the collision overlap geometry. The second-order "elliptic" harmonic moment is obtained with high precision through four-, six-, and eight-particle correlations and, for the first time, the third-order "triangular" harmonic moment is studied using four-particle correlations. A sample of peripheral PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV that covers a similar range of event multiplicities as the pPb results is also analyzed. Model calculations of initial-state fluctuations in pPb and PbPb collisions can be directly compared to the high precision experimental results. This work provides new insight into the fluctuation-driven origin of the $v_3$ coefficients in pPb and PbPb collisions, and into the dominating overall collision geometry in PbPb collisions at the earliest stages of heavy ion interactions.

Highlights

  • In collisions of ultrarelativistic heavy ions, two-particle azimuthal correlations between the large number of particles created over a broad range in pseudorapidity were first observed in gold-gold and copper-copper collisions at the BNL Relativistic Heavy Ion Collider (RHIC) [1,2,3,4], and have subsequently been studied in lead-lead (PbPb) collisions at the CERN Large Hadron Collider (LHC) [5,6,7,8,9,10,11]

  • The v2 values for PbPb collisions are higher than those for pPb collisions, which is consistent with the lenticular-shaped overlap geometry dominating this harmonic for PbPb collisions

  • The two-particle correlation v2 and v3 results are systematically higher than the multiparticle results for both pPb and PbPb collision

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Summary

Introduction

In collisions of ultrarelativistic heavy ions, two-particle azimuthal correlations between the large number of particles created over a broad range in pseudorapidity were first observed in gold-gold and copper-copper collisions at the BNL Relativistic Heavy Ion Collider (RHIC) [1,2,3,4], and have subsequently been studied in lead-lead (PbPb) collisions at the CERN Large Hadron Collider (LHC) [5,6,7,8,9,10,11]. At the LHC, long-range correlations have been observed in proton-proton

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