Collective long-range particle correlations in proton-proton and proton-nucleus collisions at the LHC with the CMS detector

TL;DR

This paper reports on measurements of long-range particle correlations in proton-proton and proton-nucleus collisions at the LHC, revealing collective behavior similar to heavy-ion collisions and showing a universal scaling of flow coefficients across different particle species.

Contribution

It provides the first detailed comparison of collective correlations in pp and pPb collisions with heavy-ion data, demonstrating a universal scaling and collective phenomena in small systems.

Findings

Observation of particle species dependence of $v_2$ in high-multiplicity events

Universal scaling of $v_2$ when normalized by constituent quarks

Comparable $v_2$ values from two-, four-, and six-particle correlations in 13 TeV pp collisions

Abstract

Measurements of two-particle angular correlations of inclusive charged particles as well as identified strange hadron in pp and pPb collisions are presented over a wide range in pseudorapidity and full azimuth. The data were collected using the CMS detector at the LHC, with nucleon-nucleon center-of-mass energy of 5.02 TeV for pPb collisions and 5, 7, 13 TeV for pp collisions. The results are compared to semi-peripheral PbPb collision data at center-of-mass energy of 2.76 TeV, covering similar charged-particle multiplicity ranges of the events. For high-multiplicity pp and pPb events, a clear particle species dependence of $v_2$ is observed for $p_{T} \lesssim 2$ GeV/c. When divided by the number of constituent quarks and compared at the same transverse kinetic energy per quark, a universal scaling over a broad range of particle transverse kinetic energy has been observed. For high-multiplicity pp collisions at 13 TeV, the $v_2$ values obtained for inclusive charged particles with two-, four- and six-particle correlations are found to be comparable within uncertainties. These measurements provide strong evidence for the collective nature of the long-range correlations observed in pp collisions.