出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：The conventional implementation of the inclusive hadronic $\tau$ decay data based, flavor-breaking (FB) finite-energy sum rule (FESR) determination of $V_{us}$ is know to produce results $>3\sigma$ low compared to kaon physics based results and 3-family-unitarity expectations. We revisit this implementation, showing that it fails a number of self-consistency tests, and that the problems originate from a breakdown of assumptions employed for treating higher dimension OPE contributions. A recently proposed alternate implementation, which cures these problems, and uses lattice data to more reliably quantify leading $D=2$ OPE uncertainties, is then briefly reviewed. Employing this new implementation, using also preliminary BaBar results for the $\tau\rightarrow K^-\pi^0\nu_\tau$ exclusive branching fraction, yields a result, $V_{us}=0.2228(23)_{exp}(6)_{th}$, in excellent agreement with that from $K_{\ell 3}$, and, within errors, with three-family-unitarity expectations. Limitations in the near-term possibilities for reducing the experimental error by the desired factor of $\sim 2$ reduction are then highlighted. These serve to motivate a new proposal for determining $V_{us}$ via a dispersive analysis employing strange hadronic $\tau$ data and lattice data in place of the OPE.
