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Based on a sample corresponding to 4.3 million produced tau-pair events, wehave studied hadronic dynamics in the decay tau- --> nu_tau pi- pi0 pi0 in datarecorded by the CLEO II detector operating at the CESR e+e- collider. The decayis dominated by the process tau --> nu_tau a_1(1260), with the a_1 mesondecaying to three pions predominantly via the lowest dimensional (mainlyS-wave) a_1 --> rho pi Born amplitude. From fits to the Dalitz plot and angularobservables, we find significant additional contributions from amplitudes fora_1 decay to sigma pi, f_0(1370) pi and f_2(1270) pi, as well as higherdimensional a_1 --> rho pi and rho' pi amplitudes. The squared sigma piamplitude accounts for ~15% of the total tau- --> nu_tau pi- pi0 pi0 rate inthe models considered. We have searched for additional contributions from tau--> nu_tau pi'(1300). We place 90% confidence level upper limits on thebranching fraction for this channel of between 1.0*10^{-4} and 1.9*10^{-4},depending on the pi' decay mode. The pi- pi0 pi0 mass spectrum is parametrizedby a Breit-Wigner form with a mass-dependent width which is specified accordingto the results of the Dalitz plot fits plus a coupling to an a_1 --> K* Kamplitude. From a chi^2 fit, we extract the pole mass and width of the a_1, aswell as the magnitude of the K* K coupling. We have also investigated theimpact of a possible contribution from the a_1'(1700) meson on this spectrum.Finally, exploiting the parity-violating angular asymmetry in a_1 --> 3pidecay, we determine the signed value of the tau neutrino helicity to beh_{\nu_\tau} = -1.02 +- 0.13(stat.) +- 0.03(syst.+model), confirming theleft-handedness of the tau neutrino.

physical review. d. particles, fields, gravitation, and cosmology/physical review. d. particles and fields

Hadronic structure in the decay<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>τ</mml:mi></mml:mrow><mml:mrow><mml:mi>−</mml:mi></mml:mrow></mml:msup></mml:mrow><mml:mo>→</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mi>τ</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mi>−</mml:mi></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>and the sign of the tau neutrino helicity

Hadronic structure in the decayτ−→ντπ−π0π0and the sign of the tau neutrino helicity