Precision tests of the J/{\psi} from full lattice QCD: mass, leptonic width and radiative decay rate to {\eta}_c

TL;DR

This study uses full lattice QCD to accurately compute the J/ψ meson's mass, leptonic width, and radiative decay rate, providing results consistent with experimental data and offering precise tests of QCD.

Contribution

First lattice QCD calculation including u, d, s sea quarks for J/ψ properties with nonperturbative normalization, achieving high-precision results.

Findings

J/ψ - η_c mass difference: 116.5(3.2) MeV

Leptonic width: 5.48(16) keV

Radiative decay rate: 2.49(19) keV

Abstract

We calculate the J/{\psi} mass, leptonic width and radiative decay rate to \gamma \eta_c from lattice QCD including u, d and s quarks in the sea for the first time. We use the Highly Improved Staggered Quark formalism and nonperturbatively normalised vector currents for the leptonic and radiative decay rates. Our results are: M_{J/\psi} -M_{\eta_c} = 116.5(3.2) MeV; \Gamma(J/{\psi} to e^+e^-) = 5.48(16) keV; \Gamma(J/{\psi} to \gamma \eta_c) = 2.49(19) keV. The first two are in good agreement with experiment, with \Gamma(J/{\psi} to e^+e^-) providing a test of a decay matrix element in QCD, independent of CKM uncertainties, to 2%. At the same time results for the time moments of the correlation function can be compared to values from the charm contribution to \Gamma(e^+e^- to hadrons), giving a 1.5% test of QCD. Our results show that an improved experimental error would enable a similarly strong test from \Gamma(J/{\psi} to \gamma \eta_c).