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

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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 fB* and fBₛ* - similar to the decay constants of the pseudoscalar mesons fB and fBₛ - 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 may be thus 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 fB*/fB=0.944±0.011 OPE±0.018 syst and fBₛ*/fBₛ=0.947±0.023 OPE±0.020 syst. Thus, both fB*/fB and fBₛ*/fBₛ are less than unity at 2.5σ and 2σ level, respectively.