Charmonium properties from lattice QCD + QED: hyperfine splitting, $J/\ddot{I}ˆ$ leptonic width, charm quark mass and $a_{\hat{I}}{¼}^c$

Abstract

We have performed the first $n_f=2+1+1$ lattice QCD computations of the properties (masses and decay constants) of ground-state charmonium mesons. Our calculation uses the HISQ action to generate quark-line connected two-point correlation functions on MILC gluon field configurations that include $u/d$ quark masses going down to the physical point, tuning the $c$ quark mass from $M_{J/\ddot{I}ˆ}$ and including the effect of the $c$ quark's electric charge through quenched QED. We obtain $M_{J/\ddot{I}ˆ}-M_{\hat{I}{\cdot }_c}$ (connected) = 120.3(1.1) MeV and interpret the difference with experiment as the impact on $M_{\hat{I}{\cdot }_c}$ of its decay to gluons, missing from the lattice calculation. This allows us to determine $\hat{I}”M_{\hat{I}{\cdot }_c}^{\mathrm{annihiln}}$ =+7.3(1.2) MeV, giving its value for the first time. Our result of $f_{J/\ddot{I}ˆ}=$ 0.4104(17) GeV, gives $\hat{I}“(J/\ddot{I}ˆ\to e^{+}{e}^{-})$=5.637(49) keV, in agreement with, but now more accurate than experiment. At the same time we have improved the determination of the $c$ quark mass, including the impact of quenched QED to give ${\overline{m}}_c(3\mathrm{GeV})$ = 0.9841(51) GeV. We have also used the time-moments of the vector charmonium current-current correlators to improve the lattice QCD result for the $c$ quark HVP contribution to the anomalous magnetic moment of the muon. We obtain $a_{\hat{I}}{¼}^c=14.638(47)\times 10^{-10}$, which is 2.5$\ddot{I}ƒ$ higher than the value derived using moments extracted from some sets of experimental data on $R(e^{+}{e}^{-}\to \mathrm{hadrons})$. This value for $a_{\hat{I}}{¼}^c$ includes our determination of the effect of QED on this quantity, $\hat{I}´a_{\hat{I}}{¼}^c=0.0313(28)\times 10^{-10}$.

Added extra discussion on QED setup, some new results to study the effects of strong isospin breaking in the sea (including new Fig. 1) and a fit stability plot for the hyperfine splitting (new Fig. 7). Version accepted for publication in PRD