Accurate decay-constant ratios fB*/fB and fBs*/fBs from Borel QCD sum rules

We present our analysis of the decay constants of the beauty vector mesons B∗ and B _s∗ within the framework of dispersive sum rules for the two-point correlator of vector currents in QCD. While the decay constants of the vector mesons f _B∗ and f _Bs∗ - similar to the decay constants of the pseudoscalar mesons f _B and f _Bs - individually have large uncertainties induced by theory parameters not known with a satisfactory precision, these uncertainties almost entirely cancel out in the ratios of vector over pseudoscalar decay constants. These ratios, thus, may be predicted with very high accuracy due to the good control over the systematic uncertainties of the decay constants gained upon application of our hadron-parameter extraction algorithm. Our final results read f _B∗/f _B = 0.944 ± 0.011 _OPE ± 0.018 _syst and f _Bs∗/f _Bs = 0.947 ± 0.023 _OPE ± 0.020 _syst. Thus, both f _B∗/f _B and f _Bs∗/f _Bs are less than unity at 2.5σ and 2σ level, respectively.