Production of $\eta_{c}(1S,2S)$ in $e^+ e^-$ and $pp$ collisions

TL;DR

This paper models the production and transition form factors of $ ext{eta}_c$ mesons in electron-positron and proton-proton collisions, comparing theoretical predictions with experimental data and exploring the effects of gluon virtualities.

Contribution

It introduces a light-front wave function approach for $ ext{eta}_c$ mesons, analyzing their production in different collision processes with various potential models.

Findings

Delayed onset of asymptotic behavior in transition form factors.

Good agreement with BaBar data for $ ext{eta}_c(1S)$.

Predictions for $ ext{eta}_c(2S)$ production at LHCb.

Abstract

We derive the light-front wave function (LFWF) representation of the $\gamma^{\star} \gamma^{\star} \to \eta_{c} (1S),\eta_{c}(2S)$ transition form factor $F(Q^2_1,Q^2_2)$ for two virtual photons in the initial state. For the LFWF, we use different models obtained from the solution of the Schr\"odinger equation for a variety of $c\bar{c}$ potentials. We compare our results to the BaBar experimental data for the $\eta_{c}(1S)$ transition form factor, for one real and one virtual photon. We observe that the onset of the asymptotic behaviour is strongly delayed and discuss applicability of the collinear and/or massless limit. In addition, we present a thorough analysis of $\eta_{c}(1S,2S)$ quarkonia hadroproduction in $k_{\perp}$-factorisation in the framework of the light-front potential approach for the quarkonium wave function. The off-shell matrix elements for the $g^{\star} g^{\star} \to \eta_{c} (1S,2S)$ vertices are derived. We discuss the importance of taking into account the gluon virtualities. We present the transverse momentum distributions of $\eta_c$ for several models of the unintegrated gluon distributions. Our calculations are performed for four distinct parametrizations for the $c\bar{c}$ interaction potential consistent with the meson spectra. We compare our results for $\eta_{c}(1S)$ to measurements by the LHCb collaboration and present predictions for $\eta_{c}(2S)$ production.