Hadronic structure in the decay [formula presented] and the sign of the tau neutrino helicity

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Based on a sample corresponding to (Formula presented) produced (Formula presented)-pair events, we have studied hadronic dynamics in the decay (Formula presented) in data recorded by the CLEO II detector operating at the CESR (Formula presented) collider. The decay is dominated by the process (Formula presented) with the (Formula presented) meson decaying to three pions predominantly via the lowest dimensional (mainly S-wave) (Formula presented) Born amplitude. From model-dependent fits to the Dalitz plot and angular observables in bins of (Formula presented) mass, we find significant additional contributions from amplitudes for (Formula presented) decay to (Formula presented) (Formula presented) and (Formula presented) as well as higher dimensional (Formula presented) and (Formula presented) amplitudes. Notably, the squared (Formula presented) amplitude accounts for approximately 15% of the total (Formula presented) rate in the models considered. The data are well described using couplings to these amplitudes that are independent of the (Formula presented) mass. These amplitudes also provide a good description for the (Formula presented) Dalitz plot distributions. We have searched for additional contributions from (Formula presented) We place (Formula presented) confidence level upper limits on the branching fraction for this channel of between (Formula presented) and (Formula presented) depending on the (Formula presented) decay mode considered. The (Formula presented) mass spectrum is parametrized by a Breit-Wigner form with a mass-dependent width which is specified according to the results of the Dalitz plot fits plus an unknown coupling to an (Formula presented) amplitude. From a (Formula presented) fit using this parametrization, we extract the pole mass and width of the (Formula presented) as well as the magnitude of the (Formula presented) coupling. We have also investigated the impact of a possible contribution from the (Formula presented) meson on this spectrum. Finally, exploiting the parity-violating angular asymmetry in (Formula presented) decay, we determine the signed value of the (Formula presented) neutrino helicity to be (Formula presented) confirming the left-handedness of the (Formula presented) neutrino. © 1999 The American Physical Society.

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Physical Review D - Particles, Fields, Gravitation and Cosmology

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