Results of the Mixed Tau-Electroproduction Sum Rule For V_us

Abstract

A sum rule for determining |V_us| from a combination of hadronic tau decay and electroproduction data is discussed. Indications of problems with analogous, purely tau-decay-based analyses, most likely associated with slow convergence of the relevant D=2 OPE series, are outlined, and advantages of the mixed sum rule approach identified. With current data, one obtains |V_us|= 0.2208 (39)_exp (3)_th, a determination amenable to significant near-term reduction in experimental error, and with the smallest theoretical error of all current |V_us| determinations.