A determination of two Michel parameters in purely leptonic tau decays

H. Albrecht, H. Ehrlichmann, T. Hamacher, R. P. 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, T. Siegmund, B. SpaanH. Thurn, D. Töpfer, D. Wegener, M. Bittner, P. Eckstein, M. Paulini, K. Reim, H. Wegener, R. Eckmann, R. Mundt, T. Oest, R. 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. I. Britton, C. E.K. 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. Tzamariudaki, R. G. Van de Water, T. S. Yoon, D. Reßing, M. Schmidtler, M. Schneider, K. R. 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, Yu Gershtein, A. Golutvin, G. Kostina, D. Litvintsev, V. Lubimov, P. Pakhlov, F. Ratnikov, S. Semenov, A. Snizhko, V. Soloshenko, I. Tichomirov, Yu Zaitsev

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Abstract

Using the ARGUS detector at the e+e- storage ring DORIS II, we have determined the Michel parameters ρ{variant} 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)(e{double barred pipe}vv) and determine ρ{variant} from the e and μ momentum spectra and ξ from the correlations between e and μ momenta. For ρ{variant} we obtain ρ{variant}τ→e = 0.79 ± 0.08 ± 0.06 and ρ{variant}τ→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)%.

Original languageEnglish
Pages (from-to)608-614
Number of pages7
JournalPhysics Letters B
Volume316
Issue number4
DOIs
StatePublished - 28 Oct 1993
Externally publishedYes

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