Form factors of ${\eta }_c$ in light front quark model

Abstract

We study the form factors of the ${\eta }_c$ meson in the light-front quark model. We explicitly show that the transition form factor of ${\eta }_c\to {\gamma }^{\ast }\gamma$ as a function of the momentum transfer is consistent with the experimental data by the BaBar collaboration, while the decay constant of ${\eta }_c$ is found to be $f_{{\eta }_c}=230.5_{-61.0}^{+52.2}$ and $303.6_{-116.4}^{+115.2}$ MeV for ${\eta }_c\sim c\bar{c}$ by using two ${\eta }_c\to \gamma \gamma$ decay widths of $5.3\pm 0.5$ and $7.2\pm 2.1$ keV, given by Particle Data Group and Lattice QCD calculation, respectively.

Comments: 9 pages, 3 figures, accepted for publication in EPJC