Hadronic structure in the decay τ-→ντπ-π 0π0 and the sign of the tau neutrino helicity

D. M. Asner, A. Eppich, J. Gronberg, T. S. Hill, D. J. Lange, R. J. Morrison, H. N. Nelson, T. K. Nelson, D. Roberts, B. H. Behrens, W. T. Ford, A. Gritsan, H. Krieg, J. Roy, J. G. Smith, J. P. Alexander, R. Baker, C. Bebek, B. E. Berger, K. BerkelmanV. Boisvert, D. G. Cassel, D. S. Crowcroft, M. Dickson, S. Von Dombrowski, P. S. Drell, K. M. Ecklund, R. Ehrlich, A. D. Foland, P. Gaidarev, R. S. Galik, L. Gibbons, B. Gittelman, S. W. Gray, D. L. Hartill, B. K. Heltsley, P. I. Hopman, D. L. Kreinick, T. Lee, Y. Liu, T. O. Meyer, N. B. Mistry, C. R. Ng, E. Nordberg, M. Ogg, J. R. Patterson, D. Peterson, D. Riley, A. Soffer, J. G. Thayer, P. G. Thies, B. Valant-Spaight, A. Warburton, C. Ward, M. Athanas, P. Avery, C. D. Jones, M. Lohner, C. Prescot, A. I. Rubiera, J. Yelton, J. Zheng, G. Brandenburg, R. A. Briere, A. Ershov, Y. S. Gao, D. Y.J. Kim, R. Wilson, T. E. Browder, Y. Li, J. L. Rodriguez, H. Yamamoto, T. Bergfeld, B. I. Eisenstein, J. Ernst, G. E. Gladding, G. D. Gollin, R. M. Hans, E. Johnson, I. Karliner, M. A. Marsh, M. Palmer, C. Plager, C. Sedlack, M. Selen, J. I. Thaler, J. Williams, K. W. Edwards, A. Bellerive, R. Janicek, P. M. Patel, A. J. Sadoff, R. Ammar, P. Baringer, A. Bean, D. Besson, D. Coppage, R. Davis, S. Kotov, I. Kravchenko, N. Kwak, X. Zhao, L. Zhou, S. Anderson, Y. Kubota, S. J. Lee, R. Mahapatra, J. J. O'Neill, R. Poling, T. Riehle, A. Smith, M. S. Alam, S. B. Athar, Z. Ling, A. H. Mahmood, S. Timm, F. Wappler, A. Anastassov, J. E. Duboscq, K. K. Gan, C. Gwon, T. Hart, K. Honscheid, H. Kagan, R. Kass, J. Lorenc, H. Schwarthoff, A. Wolf, M. M. Zoeller, S. J. Richichi, H. Severini, P. Skubic, A. Undrus, M. Bishai, S. Chen, J. Fast, J. W. Hinson, J. Lee, N. Menon, D. H. Miller, E. I. Shibata, I. P.J. Shipsey, S. Glenn, Y. Kwon, A. L. Lyon, E. H. Thorndike, C. P. Jessop, K. Lingel, H. Marsiske, M. L. Perl, V. Savinov, D. Ugolini, X. Zhou, T. E. Coan, V. Fadeyev, I. Korolkov, Y. Maravin, I. Narsky, R. Stroynowski, J. Ye, T. Wlodek, M. Artuso, S. Ayad, E. Dambasuren, S. Kopp, G. Majumder, G. C. Moneti, R. Mountain, S. Schuh, T. Skwarnicki, S. Stone, A. Titov, G. Viehhauser, J. C. Wang, S. E. Csorna, K. W. McLean, S. Marka, Z. Xu, R. Godang, K. Kinoshita, I. C. Lai, P. Pomianowski, S. Schrenk, G. Bonvicini, D. Cinabro, R. Greene, L. P. Perera, G. J. Zhou, S. Chan, G. Eigen, E. Lipeles, M. Schmidtler, A. Shapiro, W. M. Sun, J. Urheim, A. J. Weinstein, F. Würthwein, D. E. Jaffe, G. Masek, H. P. Paar, E. M. Potter, S. Prell, V. Sharma

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138 Scopus citations


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 languageEnglish (US)
Article number012002
Pages (from-to)1-22
Number of pages22
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Issue number1
StatePublished - Jan 1 2000
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics


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