What can be learned from the Belle spectrum for the decay tau- -> nutau KS pi-
Abstract
A theoretical description of the differential decay spectrum for the decay tau- -> nutau KS pi-, which is based on the contributing K pi vector and scalar form factors F+K pi(s) and F0K pi(s) being calculated in the framework of resonance chiral theory (R), 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- -> nutau KS pi-] = 0.427 +- 0.024 % by integrating the spectrum, as well as the K* resonance parameters MK* = 895.3 +- 0.2 MeV and GammaK* = 47.5 +- 0.4 MeV, where the last two errors are statistical only. From our fits, we confirm that the scalar form factor F0K 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)*10-3 and lambda''+ = (12.9 +- 0.3)*10-4, respectively.