Two particle differential transverse momentum and number density correlations in p-Pb and Pb-Pb at the LHC

TL;DR

This paper measures two-particle correlations in p-Pb and Pb-Pb collisions at the LHC to understand particle production mechanisms and flow phenomena, analyzing how these correlations evolve with collision centrality and multiplicity.

Contribution

It provides detailed measurements of $R_2$ and $P_2$ correlations, including their Fourier decompositions, and estimates non-flow contributions to flow coefficients in heavy-ion collisions.

Findings

Near-side peak width varies with collision centrality.

Harmonic coefficients show multiplicity-dependent differences.

Upper limit on non-flow effects in flow measurements.

Abstract

We present measurements of two-particle differential number correlation functions $R_{2}$ and transverse momentum correlation functions $P_{2}$, obtained from p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained using charged particles in the pseudorapidity range $|\eta| <$ 1.0, and transverse momentum range $0.2 < p_{\rm T} < 2.0$ GeV/$c$ as a function of pair separation in pseudorapidity, $|\Delta\eta|$, azimuthal angle, $\Delta\varphi$, and for several charged-particle multiplicity classes. Measurements are carried out for like-sign and unlike-sign charged-particle pairs separately and combined to obtain charge-independent and charge-dependent correlation functions. We study the evolution of the width of the near-side peak of these correlation functions with collision centrality. Additionally, we study Fourier decompositions of the correlators in $\Delta\varphi$ as a function of the pair separation $|\Delta\eta|$. Significant differences in the dependence of their harmonic coefficients on multiplicity classes are found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of non-flow contributions to flow coefficients $v_{n}$ measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in p-Pb interactions is estimated.