Two-
particle angular correlations are studied in
proton-lead collisions at a nucleon–nucleon centre-of-mass energy of
pan id="mmlsi1" class="mathmlsrc">pii=S037026931630572X&_rdoc=1&_issn=03702693&md5=0a8d8e511f67e134fb45691102694160">
p: -5px; vertical-align: middle" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S037026931630572X-si1.gif">pt>
p://origin-ars.els-cdn.com/content/image/1-s2.0-S037026931630572X-si1.gif">pt>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>, 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
pseudora
pidity, Δ
η, and relative azimuthal angle, Δ
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,
pan id="mmlsi3" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931630572X&_mathId=si3.gif&_user=111111111&_pii=S037026931630572X&_rdoc=1&_issn=03702693&md5=75c717f2912582e62db098e002f741ec" title="Click to view the MathML source">Δϕ≈0pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>, is observed in the
pseudora
pidity range
pan id="mmlsi4" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931630572X&_mathId=si4.gif&_user=111111111&_pii=S037026931630572X&_rdoc=1&_issn=03702693&md5=a06b9f4ff5695a033932b4758c676eee" title="Click to view the MathML source">2.0<η<4.9pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>. This measurement of long-range correlations on the near side in
proton-lead collisions extends
previous observations into the forward region u
p to
pan id="mmlsi5" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931630572X&_mathId=si5.gif&_user=111111111&_pii=S037026931630572X&_rdoc=1&_issn=03702693&md5=a1e692840478c5bad265a0d002117815" title="Click to view the MathML source">η=4.9pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>. 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 com
patible when com
paring events with similar absolute activity in the direction analysed.