Radiative transitions in charmonium from $N_f=2$ twisted mass lattice QCD

Abstract

We present a study for charmonium radiative transitions: $J/\psi \to {\eta }_c\gamma$, ${\chi }_{c0}\to J/\Psi \gamma$ and $h_c\to {\eta }_c\gamma$ using $N_f=2$ twisted mass lattice QCD gauge configurations. The single-quark vector form factors for ${\eta }_c$ and ${\chi }_{c0}$ are also determined. The simulation is performed at a lattice spacing of $a=0.06666$ fm and the lattice size is $32^3\times 64$. After extrapolation of lattice data at nonzero $Q^2$ to 0, we compare our results with previous quenched lattice results and the available experimental values.

Comments: typeset with revtex, 15 pages, 11 figures, 4 tables