Measurements of long-range near-side angular correlations in $\sqrt{s_{\text{NN}}}=5$TeV proton-lead collisions in the forward region

TL;DR

This paper reports the observation of long-range near-side angular correlations in proton-lead collisions at 5 TeV, extending previous measurements into the forward region and analyzing their dependence on event activity and beam direction.

Contribution

It provides the first measurement of long-range near-side correlations in the forward region in proton-lead collisions at 5 TeV, revealing dependence on event activity and beam direction.

Findings

Long-range near-side correlation observed in high-activity events.

Correlation increases with event activity and is more pronounced in the lead beam direction.

Correlations in lead and proton beam directions are compatible at similar activity levels.

Abstract

Two-particle angular correlations are studied in proton-lead collisions at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\text{NN}}}=5$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, $\Delta\eta$, and relative azimuthal angle, $\Delta\phi$, 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, $\Delta\phi \approx 0$, is observed in the pseudorapidity range $2.0<\eta<4.9$. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to $\eta=4.9$. 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.