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

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 $\eta_c \to \gamma^* \gamma$ 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 $\eta_c \to \gamma \gamma$decaywidthsof$5.3\pm 0.5$and$7.2\pm2.1$ keV, given by Particle Data Group and Lattice QCD calculation, respectively.