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

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 $<\mathrm{\mid }\eta \mathrm{\mid }<$ 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.