Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-ofmass
energy of √sN N = 5 TeV, collected with the LHCb detector at the LHC. The analysis is based on
data recorded in two beam configurations, in which either the direction of the proton or that of the
lead ion is analysed. The correlations are measured in the laboratory system as a function of relative
pseudorapidity, η, and relative azimuthal angle, φ, for events in different classes of event activity
and for different bins of particle transverse momentum. In high-activity events a long-range correlation
on the near side, φ ≈ 0, is observed in the pseudorapidity range 2.0 < η < 4.9. This measurement of
long-range correlations on the near side in proton-lead collisions extends previous observations into the
forward region up to η = 4.9. The correlation increases with growing event activity and is found to be
more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead
and proton beams are found to be compatible when comparing events with similar absolute activity in
the direction analysed.