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J/Psi production in proton induced collisions at FAIR

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 $c\bar{c}$ pair which can be reliably described by perturbative QCD, and (ii) formation of J/$ψ$ resonance from the $c\bar{c}$ 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 $x_F$, while gluon-gluon fusion dominates the production at smaller $x_F$. 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 $c\bar{c}$ 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.