Electromagnetic structure of Bc and heavy quarkonia in the light-front quark model

We investigate the electromagnetic structure of heavy quarkonia and the $B_c$ meson within the light-front quark model (LFQM) to better understand the internal spatial charge distributions and QCD dynamics of heavy mesons. The light-front wave functions (LFWFs) are obtained using a variational approach with a few set of harmonic oscillator basis functions, providing a flexible yet tractable description of the bound-state dynamics. Using these LFWFs, we compute the electromagnetic form factors and compare our results with available lattice QCD data and other model calculations. Our results are roughly consistent with previous model predictions, showing that the electromagnetic radii of the $2S$ and $3S$ states are approximately 1.5 times and 1.9 times larger than those of their corresponding $1S$ states, reflecting the expected growth of spatial size in radial excitations.