Forward $J/\psi + J/\psi$ and $J/\psi + \psi^\prime$ production with High Energy Factorization

TL;DR

This paper calculates the production cross sections of $J/$ pairs in proton-proton collisions at 13 TeV using high energy factorization, showing good agreement with recent LHCb data and highlighting the role of double parton scattering.

Contribution

It applies the $k_T$-factorization framework with CCFM evolution to describe $J/$ pair production, incorporating double parton scattering effects for the first time in this context.

Findings

The model describes recent LHCb data well.

Double parton scattering significantly affects production rates.

The ratio $\sigma(J/ + )/\sigma(J/ + J/)$ is sensitive to DPS contributions.

Abstract

We calculate the cross sections of associated $J/\psi + \psi^\prime$ and $J/\psi + J/\psi$ production in $pp$ collisions at $\sqrt s = 13$ TeV in the forward kinematic region. The High Energy Factorization ($k_T$-factorization) framework supplemented with the Catani-Ciafaloni-Fiorani-Marchesini evolution of gluon densities in a proton is applied. We demonstrate that latest data on $J/\psi + J/\psi$ production and first experimental data on $J/\psi + \psi^\prime$ events taken very recently by the LHCb Collaboration can be described well by the color singlet terms and contributions from the double parton scattering (DPS) with the standard choice for $\sigma_{\rm eff}$ parameter. The relative production rate $\sigma(J/\psi + \psi^\prime)/\sigma(J/\psi + J/\psi)$ is found to be sensitive to the DPS terms as well as to feeddown contributions.