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

Measurements of the kinematic distributions of J/ψ mesons produced in p-C, p-Ti and p-W collisions at √(s)=41.6 GeV in the Feynman-x region -0.34<xF<0.14 and for transverse momentum up to pT=5.4 GeV/c are presented. The xF and pT dependencies of the nuclear suppression parameter, α, are also given. The results are based on 2.4.105 J/ψ mesons 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 xF for the first time. The average value of α in the measured xF region is 0.981±0.015. The data suggest that the strong nuclear suppression of J/ψ production previously observed at high xF turns into an enhancement at negative xF. (orig.)