Inclusive J/ψ production in forward proton-proton and proton-lead collisions at high energy

We calculate the cross section for forward J/ψ production in proton-proton and minimum bias proton-lead collisions using the Color Glass Condensate (CGC) and Non-Relativistic QCD (NRQCD) formalism consistently with Deep Inelastic Scattering data. The cross section for color singlet states is sensitive to a 4-point correlator of Wilson lines for which we describe in the Gaussian approximation in the large-Nc limit. Furthermore, we quantify the importance of finite-Nc corrections to have a small ~ 12% effect. In contrast with the generic NRQCD expectation, we show that the color singlet contribution is only $15%$ to the total cross section. We also compare our predictions for J/ψ production as well as for the nuclear modification ratio RpPb to LHCb and ALICE data. We find a good agreement at forward rapidities, except at low transverse momenta where the cross sections are overestimated.