Inclusive production of J/$\psi$ and ${\psi }^{\prime }$ mesons at the LHC

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 ${\psi }^{\prime }\to J/\psi X$. The production of the decaying mesons (${\chi }_c$ or ${\psi }^{\prime }$)is also calculated within NRQCD $k_t$-factorization. The corresponding matrix elements for $gg\to J/\psi$, $gg\to {\psi }^{\prime }$ 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 ${\psi }^{\prime }$ 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.

Comments: 4 pages, 4 figures, a talk by A. Cisek at MESON2016 workshop, Krakow, June 2-7, 2016