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

TL;DR

This paper presents the first lattice QCD calculations of radiative transitions involving excited, high-spin, and exotic charmonium states, providing new insights into their decay widths and transition form factors.

Contribution

It introduces a novel lattice QCD approach to compute radiative transitions for exotic and excited charmonium states, including the first calculation of the exotic 1-+ eta_c1 decay.

Findings

Large partial width for eta_c1 -> J/psi gamma (~100 keV)

First calculation of electric dipole and magnetic quadrupole form factors in this framework

Significant signals for hindered magnetic dipole transitions and a non-exotic hybrid candidate

Abstract

We compute, for the first time using lattice QCD methods, radiative transition rates involving excited charmonium states, 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-+ eta_c1 radiative decay, we find a large partial width Gamma(eta_c1 -> J/psi gamma) ~ 100 keV. We find clear signals for electric dipole and magnetic quadrupole transition form factors in chi_c2 -> J/psi gamma, calculated for the first time in this framework, and study transitions involving excited psi and 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 non-exotic vector hybrid candidate Y_hyb? -> eta_c 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.