Azimuthal anisotropy harmonics from long-range correlations in high multiplicity pp collisions at CMS

Zhenyu Chen

doi:10.1016/j.nuclphysa.2016.01.045

Abstract

Measurements of two-particle angular correlations in pp collisions at s=7 TeV are presented as a function of charged-particle multiplicities. The data, corresponding to an integrated luminosity of about 6.2 pb−1, were collected during the 2010 LHC pp run using the CMS detector. In high-multiplicity events, a long-range (|Δη|>2), near-side (Δϕ≈0) structure is found in the two-particle Δη−Δϕ correlation functions. The second-order (v2) and third-order (v3) azimuthal anisotropy harmonics of charged particles, KS0 and Λ/Λ‾ particles are extracted from long-range two-particle correlations as a function of particle multiplicity and transverse momentum, after correcting for the contribution of back-to-back jet correlations. A v2 and v3 value of about 4% and 1%, averaging over 0.3<pT<3 GeV/c, are observed in the high-multiplicity region, and are found to be smaller than values obtained in pPb and PbPb collisions at similar multiplicities.

Highlights

Observation of long-range two-particle azimuthal correlations at large relative pseudorapidity in highmultiplicity proton-proton [1] and proton-lead [2] collisions at CMS has opened up new opportunities of studying novel dynamics of particle production in small but high-density Quantum Chromodynamic (QCD) systems
Various theoretical models including initial-state gluon correlations without any final-state interactions and hydrodynamic flow that develops in a conjectured high-density but spatially localized medium have been proposed to interpret the origin of the observed long-range correlations in pp and pPb [3, 4]
To provide new insights on understanding the long-range correlation phenomenon in high-multiplicity pp collisions, this paper presents an analysis of two- particle azimuthal correlations with unidentified charged particles and identified particles of KS0 and Λ/Λ

Summary

Zhenyu Chen for the CMS Collaboration

A long-range (| ∆η |> 2), near-side (∆φ ≈ 0) structure is found in the two-particle ∆η-∆φ correlation functions. Measurements of two- particle angular correlations in pp collisions at s = 7 TeV are presented as a function of charged-particle multiplicities. In high-multiplicity events, a long-range (|∆η| > 2), near-side (∆φ ≈ 0) structure is found in the two-particle ∆η-∆φ correlation functions. The second-order (v2) and third-order (v3) azimuthal anisotropy harmonics of charged particles, KS0 and Λ/Λ particles are extracted from long-range two-particle correlations as a function of particle multiplicity and transverse momentum, after correcting for the contribution of back-to-back jet correlations. A v2 and v3 value of about 4% and 1%, averaging over 0.3 < pT < 3 GeV/c, are observed in the high-multiplicity region, and are found to be smaller than values obtained in pPb and PbPb collisions at similar multiplicities

Introduction

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Results