Exotic and excited-state radiative transitions in charmonium from lattice QCD

Abstract

We compute, for the first time using lattice QCD methods, charmonium radiative transition rates involving states of high spin and exotics. Utilizing a large basis of interpolating fields we are able to project out various excited-state contributions to three-point correlators computed on quenched anisotropic lattices. In the first lattice QCD calculation of the exotic ${1}^{\ensuremath{-}+}$ ${\ensuremath{\eta}}_{c1}$ radiative decay, we find a large partial width $\ensuremath{\Gamma}({\ensuremath{\eta}}_{c1}\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\gamma})\ensuremath{\sim}100\text{ }\text{ }\mathrm{keV}$. We find clear signals for electric dipole and magnetic quadrupole transition form factors in ${\ensuremath{\chi}}_{c2}\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\gamma}$, calculated for the first time in this framework, and study transitions involving excited $\ensuremath{\psi}$ and ${\ensuremath{\chi}}_{c1,2}$ states. We calculate hindered magnetic dipole transition widths without the sensitivity to assumptions made in model studies and find statistically significant signals, including a nonexotic vector hybrid candidate ${Y}_{\mathrm{hyb}?}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}\ensuremath{\gamma}$. As well as comparison to experimental data, we discuss in some detail the phenomenology suggested by our results and the extent to which it mirrors that of quark-potential models, and make suggestions for the interpretation of our results involving exotic quantum numbered states.