Decay constants of heavy mesons from QCD sum rules
Abstract
We present a sum-rule extraction of the decay constants of the D, Ds, B, and Bs mesons from the two-point correlator of heavy-light pseudoscalar currents [1]. Our main emphasis is laid on the control over 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 due to the application of our novel procedure for extracting hadron observables based on a dual threshold depending on the Borel parameter. For charmed mesons, we obtain fD=206.2 7.3 (OPE) 5.1 (syst) MeV and fDs=245.3 15.7 (OPE) 4.5 (syst) MeV. For beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of the MSbar mass of the b-quark, mb(mb). By requiring our sum-rule estimate to match the average of lattice determinations of fB, a very accurate value is extracted, mb(mb)=4.245 0.025 GeV, yielding fB = 193.4 12.3 (OPE) 4.3 (syst) MeV and fBs = 232.5 18.6 (OPE) 2.4 (syst) MeV.
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