Michel parameters and τ neutrino helicity from decay correlations in Z → τ+τ-

D. Buskulic, D. Casper, I. De Bonis, D. Decamp, P. Ghez, C. Goy, J. P. Lees, M. N. Minard, P. Odier, B. Pietrzyk, F. Ariztizabal, M. Chmeissani, J. M. Crespo, I. Efthymiopoulos, E. Fernandez, M. Fernandez-Bosman, V. Gaitan, Ll Garrido, M. Martinez, S. OrteuA. Pacheco, C. Padilla, F. Palla, A. Pascual, J. A. Perlas, F. Sanchez, F. Teubert, D. Creanza, M. de Palma, A. Farilla, G. Iaselli, G. Maggi, N. Marinelli, S. Natali, S. Nuzzo, A. Ranieri, G. Raso, F. Romano, F. Ruggieri, G. Selvaggi, L. Silvestris, P. Tempesta, G. Zito, X. Huang, J. Lin, O. Ouyang, T. Wang, Y. Xie, R. Xu, S. Xue, J. Zhang, L. Zhang, W. Zhao, G. Bonvicini, M. Cattaneo, P. Comas, P. Coyle, H. Drevermann, A. Engelhardt, R. W. Forty, M. Frank, G. Ganis, M. Girone, R. Hagelberg, J. Harvey, R. Jacobsen, B. Jost, J. Knobloch, I. Lehraus, M. Maggi, C. Markou, E. B. Martin, P. Mato, H. Meinhard, A. Minten, R. Miquel, P. Palazzi, J. R. Pater, P. Perrodo, J. F. Pusztaszeri, F. Ranjard, L. Rolandi, D. Schlatter, M. Schmelling, W. Tejessy, I. R. Tomalin, R. Veenhof, A. Venturi, H. Wachsmuth, W. Wiedenmann, T. Wildish, W. Witzeling, J. Wotschack, Z. Ajaltouni, M. Bardadin-Otwinowska, A. Barres, C. Boyer, A. Falvard, P. Gay, C. Guicheney

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Abstract

The Michel parameters and the average τ-neutrino helicity are measured using correlations between the decays of the τ+ and τ- produced on the Z resonance and observed in the ALEPH detector at LEP. The Michel parameters, ρ{variant}l, ηl, ξl, (δξ)l, are determined from τ → lνlντ with l = (e, μ), and the average τ neutrino helicity, 〈h(ντ)〉, from τ → hν with h = (π, ρ{variant}, a1). The results obtained with e-μ universality are: ρ{variant}l = 0.751±0.039±0.022, ηl = -0.04±0.15±0.11, ξl = 1.18±0.15±0.06, (δξ)l = 0.88±0.11±0.07, and the average τ neutrino helicity 〈h(ντ)〉 = -1.006±0.032±0.019. No significant deviation from the Standard Model V-A prediction is observed. © 1995.
Original languageEnglish
Pages (from-to)379-388
JournalPhysics Letters B
Volume346
Issue number3-4
DOIs
Publication statusPublished - 9 Mar 1995

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