The $\eta_c\gamma \gamma ^*$ transition form factor in the decay $\eta_c\to \gamma \ell^+\ell^-$ and in the crossed channels $\gamma e^-\to \eta_c e^- $ and $e^+e^-\to\eta_c\gamma$

E. Di Salvo; M.P. Rekalo; E. Tomasi-Gustafsson

doi:doi:10.1007/s100520050022

EPJ

The $\eta_c\gamma \gamma ^*$ transition form factor in the decay $\eta_c\to \gamma \ell^+\ell^-$
and in the crossed channels $\gamma e^-\to \eta_c e^-$ and $e^+e^-\to\eta_c\gamma$

E. Di Salvo¹ - M.P. Rekalo² - E. Tomasi-Gustafsson³

¹ Dipartimento di Fisica dell' Università di Genova and I.N.F.N. - Sez. Genova, Via Dodecaneso 33, 16146 Genova, Italy
² Middle East Technical University, Physics Department, Ankara 06531, Turkey
³ DAPNIA/SPhN, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France

Abstract
The Dalitz distribution and the effective mass spectrum of the lepton pair produced in the decay $\eta_c\to \gamma \ell^+\ell^-$ , as well as the differential cross sections for the crossed channels $\gamma e^-\to \eta_c e^-$ and $e^+e^-\to\eta_c\gamma$ , are calculated in terms of the sole electromagnetic transition form factor for the vertex $\eta_c\to\gamma \gamma^*$ , where $\gamma^*$ is a virtual photon with a space-like (for $\gamma e^-\to \eta_c e^-$ ) or a time-like (for $e^+e^-\to\eta_c\gamma$ and $\eta_c\to \gamma \ell^+\ell^-$ ) four-momentum. Explicit parameterizations of the transition form factor are found in two different approaches, namely in the vector dominance model and in a QCD-inspired consideration on the basis of the process $c \overline{c}\to \gamma \ell^+ \ell^-$ , with zero relative three-momentum of the annihilating quarks.

Winter Workshop on Complex Systems
21-26 January 2024
Catalonia, Spain

EPJ

The transition form factor in the decay and in the crossed channels and

Conference announcements

The $\eta_c\gamma \gamma ^*$ transition form factor in the decay $\eta_c\to \gamma \ell^+\ell^-$
and in the crossed channels $\gamma e^-\to \eta_c e^-$ and $e^+e^-\to\eta_c\gamma$