Inclusive $\mathrm{J}/\psi$ production in forward proton-proton and proton-lead collisions at high energy

TL;DR

This paper calculates forward J/ψ production in proton-proton and proton-lead collisions using CGC and NRQCD, showing that color singlet states contribute only 15% and comparing predictions with LHC data.

Contribution

It provides a consistent calculation of J/ψ production combining CGC and NRQCD, including finite-Nc corrections and a detailed analysis of color singlet contributions.

Findings

Color singlet contribution is about 15% of total cross section.

Finite-Nc corrections have a small (~12%) effect.

Predictions agree with LHCb and ALICE data at forward rapidities.

Abstract

We calculate the cross section for forward $\mathrm{J}/\psi$ 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-$N_c$ limit. Furthermore, we quantify the importance of finite-$N_c$ corrections to have a small $\sim 12\%$ 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 $\mathrm{J}/\psi$ production as well as for the nuclear modification ratio $R_{pPb}$ to LHCb and ALICE data. We find a good agreement at forward rapidities, except at low transverse momenta where the cross sections are overestimated.