Charmonium properties from lattice QCD + QED: Hyperfine splitting, J/ψ leptonic width, charm quark mass, and acμ

• Published in: Physical review. D 2020-09, Vol.102 (5), p.1
• Main Authors: Hatton, D, Davies, C T H, Galloway, B, Koponen, J, Lepage, G P, Lytle, A T
• Format: Article
• Language: English
• Subjects: Charm (particle physics); Correlators; Decay rate; Gluons; Hadrons; Magnetic moments; Mathematical analysis; Mesons; Quantum chromodynamics; Quarks; Quenching
• ISSN: 2470-0010; 2470-0029
• DOI: 10.1103/PhysRevD.102.054511

We have performed the first nf = 2 + 1 + 1 lattice QCD computations of the properties (masses and decay constants) of ground-state charmonium mesons. Our calculation uses the Highly Improved Staggered Quark (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 / ψ and including the effect of the c quark's electric charge through quenched QED. We obtain MJ/ψ − Mηc (connected) = 120.3 (1.1) MeV and interpret the difference with experiment as the impact on Mηc of the ηc decay to gluons, missing from the lattice calculation. This allows us to determine ΔM annihilnηc = + 7.3 (1.2) MeV, giving its value for the first time. Our result of fJ/ψ = 0.4104 (17) GeV gives Γ J / ψ → 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 mc (3 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 hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon. We obtain acμ = 14.638 (47) × 10−10, which is 2.5 σ higher than the value derived using moments extracted from some sets of experimental data on R (e+ e− → hadrons) . This value for acμ includes our determination of the effect of QED on this quantity, δacμ = 0.0313 (28) × 10−10 .