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
Summary
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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