Prompt hadroproduction of C-even quarkonia in the light-front $k_T$ -factorization approach

TL;DR

This paper introduces a new $k_T$-factorization approach to prompt C-even quarkonium production, emphasizing the role of off-shell gluon fusion and light-front wave functions, with applications to LHCb data.

Contribution

It develops a novel $k_T$-factorization method for quarkonium production using light-front wave functions, providing new insights into gluon fusion processes at small-$x$.

Findings

Calculated off-shell matrix elements for quarkonia production.

Compared theoretical results with LHCb data for $ ext{eta}_c$.

Discussed photon transition form factors and cross sections.

Abstract

We present a new approach for the prompt production of quarkonia which is based on the $k_T$-factorization method. The production of even C-parity quarkonia proceeds via the fusion of two (off-shell) gluons. Especially in the kinematics of the LHCb experiment these processes are thus expected to be a sensitive probe of the small-$x$ gluon distribution. We calculate the relevant off-shell matrix elements in terms of the light-front wave functions of the quarkonium states. We present our results for scalar and pseudoscalar charmonia and discuss photon transition form factors as well as cross sections for prompt hadroproduction. We compare our results for the $\eta_c$ to recent LHCb data.