Rapidity and multiplicity dependence of charged-particle flow in $p$Pb collisions at $\sqrt{s_{NN}} = 8.16$ TeV

TL;DR

This study measures elliptic and triangular flow of charged particles in proton-lead collisions at 8.16 TeV, analyzing how flow varies with multiplicity and transverse momentum, and compares results with theoretical models.

Contribution

It provides detailed flow measurements in pPb collisions at 8.16 TeV and evaluates the performance of a (3+1)D dynamic model against experimental data.

Findings

The (3+1)D model overestimates elliptic flow.

No significant difference in flow between forward and backward regions.

Flow effects likely dominate over initial-state effects in small systems.

Abstract

The elliptic and triangular flow of charged particles are measured using two-particle angular correlations in $p$Pb collisions in the pseudorapidity range \cal{2.0 $< |\eta| <$ 4.8}. The data sample was collected by the LHCb experiment in 2016 at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}} = 8.16$ TeV, containing in total approximately 1.5 billion collision events. Non-flow contributions are obtained in low-multiplicity collisions and subtracted to extract the flow harmonics. The results are presented as a function of event multiplicity and hadron transverse momentum. Comparisons with a full (3+1)D dynamic model indicate that it overestimates the measured elliptic flow. A comparison between the forward and backward regions reveals no significant differences in flow parameters, suggesting that final-state effects may dominate over initial-state effects in the origin of flow in small systems.