What can be learned from the Belle spectrum for the decay τ- → νtKSπ-

A theoretical description of the differential decay spectrum for the decay tau(-) -> nu K-tau(S)pi(-), which is based on the contributing K pi vector and scalar form factors F-+(K pi)(s) and F-0(K pi)(s) being calculated in the framework of resonance chiral theory (R chi T), additionally imposing constraints from dispersion relations as well as short distance QCD, provides a good representation of a recent measurement of the spectrum by the Belle Collaboration. Our fit allows to deduce the total branching fraction B[tau(-) -> v(tau)K(S)pi(-)] = 0.427 +/- 0.024% by integrating the spectrum, as well as the K* resonance parameters M-K* = 895.3 +/- 0.2 MeV and Gamma(K)* = 47.5 +/- 0.4 MeV, where the last two errors are statistical only. From our fits, we confirm that the scalar form factor F-0(K pi)(S) is required to provide a good description, but we were unable to further constrain this contribution. Finally, from our results for the vector form factor F-+(K pi) (S), we update the corresponding slope and curvature parameters lambda(+)' = (25.2 +/- 0.3) x 10(-3) and lambda(+)'' = (12.9 +/- 0.3) x 10(-4), respectively. (C) 2008 Elsevier B.V. All rights reserved.