Two-particle correlations in $p$-Pb collisions at the LHCb

This paper describes the analysis of two-particle angular correlations in proton–lead collisions at $\sqrt{s_{NN}}$ = 5 TeV nucleon–nucleon center-of-mass energy performed by the LHCb experiment. Correlations in function of relative pseudorapidity $\Delta \eta$ and relative azimuthal angle $\Delta \phi$ are measured in different event activity classes and bins of particle transverse momentum. The analysis is done separately for the two beam configurations corresponding to the two proton beam directions. Long-range near-side correlations are observed in high-activity events, thus extending previous analyses of this effect to the forward region (2.0 < $\eta$ < 4.9). The near-side effect becomes stronger with increasing event activity and seems to be more prominent in the lead–proton mode. However, when comparing both beam configurations for events with similar absolute activity, the results are compatible with each other.