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A determination of two Michel parameters in purely leptonic tau decays

1993; Elsevier BV; Volume: 316; Issue: 4 Linguagem: Inglês

10.1016/0370-2693(93)91051-n

1873-2445

H. Albrecht, H. Ehrlichmann, T. Hamacher, Ralf Hofmann, A. Kirchhoff, A. Nau, S. Nowak, H. Schröder, H.D. Schulz, M. Walter, R. Wurth, C. Hast, H. Kolanoski, A. Kosche, A. Lange, A. Lindner, R. Mankel, M. Schieber, Thomas Siegmund, B. Spaan, H. Thurn, D. Töpfer, D. Wegener, Michael Bittner, P. Eckstein, M. Paulini, K. Reim, H. Wegener, R. Eckmann, R. Mundt, T. Oest, Robert Reiner, W. Schmidt‐Parzefall, W. Funk, J. Stiewe, S. Werner, K. Ehret, W. Hofmann, A. Hüpper, S. Khan, K.T. Knöpfle, M. Seeger, J. Spengler, D. Britton, C. Charlesworth, K. W. Edwards, E. R. F. Hyatt, H. Kapitza, P. Krieger, D. B. MacFarlane, P. M. Patel, J.D. Prentice, P.R.B. Saull, K. Tzamariúdaki, R. G. Van de Water, T.-S. Yoon, D. Reβing, M. Śchmidtler, M. Schneider, Klaus Schubert, K. Strahl, R. Waldi, S. Weseler, G. Kernel, P. Križan, E. Križnič, T. Podobnik, T. Živko, V. Balagura, I. Belyaev, S. Chechelnitsky, M. Danilov, A. Droutskoy, Y. Gershtein, A. Golutvin, G. Kostina, D. O. Litvintsev, V. Lubimov, P. Pakhlov, F. Ratnikov, S. Semenov, A. Snizhko, V. Soloshenko, I. Tichomirov, Yu. Zaitsev,

Neutrino Physics Research

Using the ARGUS detector at the e+e− storage ring DORIS II, we have determined the Michel parameters ϱ and ξ of τ → μνν and τ → eνν decays. From a data sample with 333 events/pb around s = 10 GeV, we select 3230 events e+e− → τ+τ− → (μ±μμ)(eǂvv) and determine ϱ from the e and μ momentum spectra and ξ from the correlations between e and μ momenta. For ϱ we obtain ϱτ→e = 0.79 ± 0.08 ± 0.06 and ϱτ→μ = 0.76 ± 0.08 in accordance with the V - A structure of the decays. The momentum correlations are only sensitive to the product ξτ→eξτ→μ. Setting ξτ→e = ξτ→μ, we obtain |ξτ| = 0.90 ± 0.15 ± 0.10 also in accordance with V - A. The updated decay fractions are B(τ → evv) = (17.5 ± 0.3 ± 0.5)% and B(τ → μvv) = (17.4 ± 0.3 ± 0.5)%.