Vus from hadronic τ decays

We study the reliability of extractions of |Vus| based on flavor-breaking hadronic τ decay sum rules. The “(0,0) spectral weight”, proposed previously as a favorable candidate for this extraction, is shown to produce results having poor stability with respect to s0, the upper limit on the relevant spectral integral, suggesting theoretical errors much larger than previously anticipated. We argue that this instability is due to the poor convergence of the integrated D=2 OPE series. Alternate weight choices designed to bring this convergence under better control are shown to produce significantly improved stability, and determinations of |Vus| which are both mutually compatible, and consistent, within errors, with values obtained by other methods.