The Ds And D Leptonic Decay Constants From Lattice Qcd PDF Download

Recent calculations of the decay constants in lattice QCD are reviewed and compared to experiment. The decay constants are tabulated in Table 2 and plotted in Figure 2. The most precise f{sub Ds} value is from HPQCD. It is about 2[sigma] higher than their previous result. The change is due to a more precise determination of the lattice spacing and better tuning of the quark masses. They have updated f{sub D+} using the new f{sub Ds} and their older f{sub Ds}/f{sub D+} ratio which is expected to be less sensitive to mistuning of the lattice spacing and masses. The preliminary FNAL/MILC f{sub Ds} value is about 1.4[sigma] higher than the HPQCD result but with a larger error. The f{sub D+} values, however, are in better agreement. FNAL/MILC expect to finalize their results once the charm quark mass tuning is complete. The two flavor ETM f{sub D+} value is about 1.6[sigma] lower than the HPQCD value while f{sub Ds} is in better agreement. It is not clear how much of the difference is from neglecting the strange sea quark, given the errors. Lattice and experiment differ most significantly for f{sub Ds}. Figure 3 shows Kronfeld's (updated) history of f{sub Ds}. The yellow bands depict the evolution of the experimental average while the three-flavor lattice average is shown in grey. The right-hand scale and green lines show the differences in sigmas. The 3.8[sigma] discrepancy around t ≈ 2 provoked the 'f{sub Ds} puzzle'. That discrepancy has now shrunk to 1.6[sigma]. Future lattice and experiment will be decisive.