Heavy-meson decay constants from QCD sum rules.

We sketch a recent sum-rule extraction of the decay constants of the heavy pseudoscalar mesons D, Ds, B, and Bs from the two-point correlator of heavy-light pseudoscalar currents [1]. Our main emphasis lies on the control over all the uncertainties in the decay constants, related both to the input QCD parameters and to the limited accuracy of the method of sum rules. Gaining this control has become possible by application of our new procedure of extracting hadron observables based on a dual threshold depending on the Borel parameter. For the charmed-meson decay constants, we find <DFORMULA>fD = (206.2±7.3(OPE)±5.1syst)) MeV,</DFORMULA> <DFORMULA>fDs = (245.3±15.7(OPE)±4.5(syst)) MeV.</DFORMULA> For the beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of the <DFORMULA><OVERLINE>MS</OVERLINE></DFORMULA> mass of the b-quark, <OVERLINE>m</OVERLINE>b(<OVERLINE>m</OVERLINE>b). By requiring our sum-rule estimate to match the average of the lattice determinations of fB, we extract the rather accurate value <DFORMULA><OVERLINE>m</OVERLINE>b(<OVERLINE>m</OVERLINE>b) = (4.245±0.025) GeV</DFORMULA> Feeding this parameter value into our sum-rule formalismleads to the beauty-meson decay constants <DFORMULA>fB = (193.4±12.3(OPE)±4.3(syst)) MeV,</DFORMULA> <DFORMULA>fBs = (232.5±18.6(OPE)±2.4syst)) MeV.</DFORMULA> [ABSTRACT FROM AUTHOR]