Production of η and η mesons in pp and pPb collisions

Abstract

The production of η and η mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of 5.02 and 13 TeV and proton-lead collisions are studied at a center-of-mass energy per nucleon of 8.16 TeV. The studies are performed in center-of-mass (c.m.) rapidity regions 2.5 < yc.m. < 3.5 (forward rapidity) and −4.0 < yc.m. < −3.0 (backward rapidity) defined relative to the proton beam direction. The η and η production cross sections are measured differentially as a function of transverse momentum for 1.5 < pT < 10 GeV and 3 < pT < 10 GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for η and η mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of η mesons are also used to calculate η/π0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as η and η meson fragmentation.