Inclusive production of J/$\psi$ and $\psi'$ mesons at the LHC

TL;DR

This paper models the prompt production of J/ψ and ψ' mesons at the LHC using NRQCD k_t-factorization, successfully matching experimental data and exploring gluon saturation effects.

Contribution

It provides a detailed NRQCD k_t-factorization calculation of J/ψ and ψ' production, including feed-down contributions, and compares results with experimental data, highlighting the small role of color-octet mechanisms.

Findings

The model reproduces the ratio of χ_c(2) to χ_c(1) cross sections more accurately.

Differential distributions in rapidity agree with ALICE and LHCb data.

Gluon saturation effects may be relevant at forward/backward rapidities.

Abstract

We discuss the prompt production of $J/\psi$ mesons in proton-proton collisions at the LHC within a NRQCD $k_{t}$-factorization approach using Kimber-Martin-Ryskin (KMR) unintegrated gluon distributions (UGDF). We include both direct color-singlet production ($gg \to J/\psi$g) as well as a feed-down from $\chi_{c} \to J/\psi \gamma$ and $\psi' \to J/\psi X$. The production of the decaying mesons ($\chi_{c}$ or $\psi'$)is also calculated within NRQCD $k_{t}$-factorization. The corresponding matrix elements for $gg \to J/\psi$, $gg \to \psi'$ and $gg \to \chi_{c}$ include parameters of the nonrelativistic spatial wave functions of quarkonia at $r=0$, which are taken from potential models from the literature. We get the ratio of the corresponding of the cross sections for $\chi_{c}(2)$-to-$\chi_{c}(1)$ much closer to experimental data than obtained in recent analyses. Differential distributions in rapidity of $J/\psi$ and $\psi'$ are calculated and compared to experimental data of the ALICE and LHCb collaborations. We discuss possible onset of gluon saturation effects at forward/backward rapidities. One can describe the experimental data for $J/\psi$ production within model uncertainties with color-singlet component only. Therefore our theoretical results leave only a relatively small room for the color-octet contributions.