Kinematic distributions and nuclear effects of J/ψ production in 920 GeV fixed-target proton-nucleus collisions

Abstract

Measurements of the kinematic distributions of J/ψ mesons produced in p-C, p-Ti and p-W collisions at sqrt{s}=41.6∼\mathrm{GeV}$ in the Feynman-x region -0.34 <0.14 and for transverse momentum up to p T =5.4 GeV/c are presented. The x F and p T dependencies of the nuclear suppression parameter, α, are also given. The results are based on 2.4×105 J/ψ mesons reconstructed in both the e + e - and μ + μ - decay channels. The data have been collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The measurement explores the negative region of x F for the first time. The average value of α in the measured x F region is 0.981±0.015. The data suggest that the strong nuclear suppression of J/ψ production previously observed at high x F turns into an enhancement at negative x F . © 2009 Springer-Verlag / Società Italiana di Fisica.