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

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 ?0 production cross section is measured differentially in transverse momentum (pT) for 1.5<pT<10.0 GeV and in center-of-mass pseudorapidity (?c.m.) regions 2.5<?c.m.<3.5 (forward) and -4.0<?c.m.<-3.0 (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of ?0 production, while the backward measurement shows the first evidence of ?0 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. copy; 2023 CERN, for the LHCb Collaboration.