J/Psi production in proton induced collisions at FAIR

Abstract

We have examined the production of J/ψ mesons in high energy proton-proton and proton-nucleus collisions at beam energies in the range from 158 GeV to 920 GeV, available from different fixed target experiments. In the employed model J/ψ production in hadronic collisions is assumed to be a factorisable two step process: (i) production of a cc pair which can be reliably described by perturbative QCD, and (ii) formation of J/ψ resonance from the cc pair, which can be conveniently parameterized incorporating different existing physical mechanisms of color neutralization. We show that, for lower collision energies, J/ψ production through quark-anti-quark annihilation gives larger contribution at higher xF , while gluon-gluon fusion dominates the production at smaller xF . For proton-nucleus collisions the model takes into account both the initial state modification of parton distributions in nuclei and the final state interaction of the produced cc pairs with the target nucleons. The model is found to give reasonable description of data on J/ψ production in protonic and proton-nucleus collisions, for different existing fixed target experiments. In case of proton-nucleus collisions, our calculations show a non-negligible dependence of the final state nuclear dissociation of J/ψ mesons on the energy of the incident proton beam. The model has been applied to predict the J/ψ production and suppression expected in proton-nucleus collisions at energies relevant to FAIR, the upcoming accelerator facility at Darmstadt, Germany. The amount of suppressions, for different mechanisms of J/ψ hadronization has been found to be distinguishably different which might help an experimental settlement of the much controversial issue of color neutralization.