Exploiting recently proposed novel improvements of the techniques used for extracting from QCD sum rules pivotal hadron characteristics, including their systematic errors, we succeed to achieve a conspicuous agreement of the predictions of QCD sum rules for the decay constants $f_B$ and $f_{ B_s}$ of the heavy pseudoscalar mesons $B$ and $B_s,$ which before tended to be slightly too large, with corresponding results from lattice QCD. Adopting for the crucial $b$-quark $\bar{ \rm MS}$ mass the value $\bar{ m}_b(\bar{ m}_b)=(4.247\pm0.034)$ GeV, we get $f_B=(192.0\pm14.6)$ MeV and $f_{ B_s}=(228.0\pm19.8)$ MeV; clearly, this may be also viewed as a determination of the $b$-quark mass from sufficiently precise decay constants.
Categories: hep-ph hep-lat nucl-th