Radiative decays of charmonia on the lattice

TL;DR

This lattice QCD study calculates radiative decay rates of charmonia, providing precise results for decay widths and hyperfine splitting, advancing understanding of charmonium properties and decay mechanisms.

Contribution

The paper presents the first continuum-limit lattice QCD calculations of radiative decay widths for J/psi and hc to eta_c gamma, including hyperfine splitting, with dynamical quarks.

Findings

Gamma(J/psi -> eta_c gamma) = 2.64(11) keV

Gamma(hc -> eta_c gamma) = 0.72(5) MeV

Hyperfine splitting Delta = 112(4) MeV

Abstract

We present the results of our lattice QCD study of the hadronic matrix elements relevant to the physical radiative J/psi -> eta_c gamma and hc -> eta_c gamma decays. From computations with Nf=2 dynamical quark in twisted mass QCD at four lattice spacings, we were able to take the continuum limit and obtained Gamma(J/psi -> eta_c gamma) = 2.64(11) keV and Gamma(hc -> eta_c gamma) = 0.72(5) MeV. We also computed the the hyperfine splitting and found that it does not depend from the sea quark mass and we obtain Delta = m_J/psi - m_eta_c = 112(4) MeV.