Nuclear Modification Factor of Neutral Pions in the Forward and Backward Regions in p-Pb Collisions

Abstract

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16 TeV with the LHCb detector. The π0 production cross section is measured differentially in transverse momentum (pT) for 1.5 < pT < 10.0 GeV and in center-of-mass pseudorapidity (ηc:m:) regions 2.5 < ηc:m: < 3.5 (forward) and −4.0 < ηc:m: < −3.0 (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of π0 production, while the backward measurement shows the first evidence of π0 enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.