6533b7d6fe1ef96bd1266fb1

RESEARCH PRODUCT

What can be learned from the Belle spectrum for the decay τ−→ντKSπ−

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Abstract A theoretical description of the differential decay spectrum for the decay τ − → ν τ K S π − , which is based on the contributing Kπ vector and scalar form factors F + K π ( s ) and F 0 K π ( s ) being calculated in the framework of resonance chiral theory (R χ 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 [ τ − → ν τ K S π − ] = 0.427 ± 0.024 % by integrating the spectrum, as well as the K ∗ resonance parameters M K ∗ = 895.3 ± 0.2 MeV and Γ 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 π ( 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 π ( s ) , we update the corresponding slope and curvature parameters λ + ′ = ( 25.2 ± 0.3 ) × 10 −3 and λ + ″ = ( 12.9 ± 0.3 ) × 10 −4 , respectively.