Based on a sample corresponding to 4.3×106 produced τ-pair events, we have studied hadronic dynamics in the decay τ-→ντπ-π 0π0 in data recorded by the CLEO II detector operating at the CESR e+e- collider. The decay is dominated by the process τ-→ντa1-(1260), with the a1- meson decaying to three pions predominantly via the lowest dimensional (mainly S-wave) ρ-π0 Born amplitude. From model-dependent fits to the Dalitz plot and angular observables in bins of 3 π mass, we find significant additional contributions from amplitudes for a1 decay to σπ, f0(1370)π, and f2(1270)π, as well as higher dimensional a1→ρπ and ρ′ π amplitudes. Notably, the squared σπ amplitude accounts for approximately 15% of the total τ- →ντπ-π0π0 rate in the models considered. The data are well described using couplings to these amplitudes that are independent of the 3π mass. These amplitudes also provide a good description for the τ- →ντπ-π0π0 Dalitz plot distributions. We have searched for additional contributions from τ-→ντπ′ -(1300). We place 90% confidence level upper limits on the branching fraction for this channel of between 1.0×10-4 and 1.9×10-4, depending on the π′ decay mode considered. The π-π0π0 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 a1→K*K amplitude. From a χ2 fit using this parametrization, we extract the pole mass and width of the a1, as well as the magnitude of the K*K coupling. We have also investigated the impact of a possible contribution from the a1′(1700) meson on this spectrum. Finally, exploiting the parity-violating angular asymmetry in a1→3π decay, we determine the signed value of the τ neutrino helicity to be hντ=-1.02±0.13 (stat)±0.03 (syst+model), confirming the left-handedness of the τ neutrino.
|Original language||English (US)|
|Number of pages||22|
|Journal||Physical Review D - Particles, Fields, Gravitation and Cosmology|
|State||Published - Jan 1 2000|