Measurement of branching ratios and τ polarization from τ→eνν-,τ→μνν-,andτ→π(K)ν decays at LEP

G. Alexander, J. Allison, P. P. Allport, K. J. Anderson, S. Arcelli, J. C. Armitage, P. Ashton, A. Astbury, D. Axen, G. Azuelos, G. A. Bahan, J. T.M. Baines, A. H. Ball, J. Banks, G. J. Barker, R. J. Barlow, J. R. Batley, G. Beaudoin, A. Beck, J. BeckerT. Behnke, K. W. Bell, G. Bella, S. Bethke, O. Biebel, U. Binder, I. J. Bloodworth, P. Bock, H. M. Bosch, S. Bougerolle, B. B. Brabson, H. Breuker, R. M. Brown, R. Brun, A. Buijs, H. J. Burckhart, P. Capiluppi, R. K. Carnegie, A. A. Carter, J. R. Carter, C. Y. Chang, D. G. Charlton, J. T.M. Chrin, P. E.L. Clarke, I. Cohen, W. J. Collins, J. E. Conboy, M. Cooper, M. Couch, M. Coupland, M. Cuffiani, S. Dado, G. M. Dallavalle, S. De Jong, P. Debu, M. M. Deninno, A. Dieckmann, M. Dittmar, M. S. Dixit, E. Duchovni, G. Duckeck, I. P. Duerdoth, D. J.P. Dumas, G. Eckerlin, P. A. Elcombe, P. G. Estabrooks, E. Etzion, F. Fabbri, M. Fincke-Keeler, H. M. Fischer, D. G. Fong, C. Fukunaga, A. Gaidot, O. Ganel, J. W. Gary, J. Gascon, R. F. McGowan, N. I. Geddes, C. Geich-Gimbel, S. W. Gensler, F. X. Gentit, G. Giacomelli, V. Gibson, W. R. Gibson, J. D. Gillies, J. Goldberg, M. J. Goodrick, W. Gorn, C. Grandi, E. Gross, J. Hagemann, G. G. Hanson, M. Hansroul, C. K. Hargrove, P. F. Harrison, J. Hart, P. M. Hattersley, M. Hauschild, C. M. Hawkes, E. Heflin, R. J. Hemingway, R. D. Heuer, J. C. Hill, S. J. Hillier, D. A. Hinshaw, C. Ho, J. D. Hobbs, P. R. Hobson, D. Hochman, B. Holl, R. J. Homer, S. R. Hou, C. P. Howarth, R. E. Hughes-Jones, R. Humbert, P. Igo-Kemenes, H. Ihssen, D. C. Imrie, L. Janissen, A. Jawahery, P. W. Jeffreys, H. Jeremie, M. Jimack, M. Jobes, R. W.L. Jones, P. Jovanovic, D. Karlen, K. Kawagoe, T. Kawamoto, R. K. Keeler, R. G. Kellogg, B. W. Kennedy, C. Kleinwort, D. E. Klem, T. Kobayashi, T. P. Kokott, S. Komamiya, L. Köpke, R. Kowalewski, H. Kreutzmann, J. von Krogh, J. Kroll, M. Kuwano, P. Kyberd, G. D. Lafferty, F. Lamarche, W. J. Larson, J. G. Layter, P. Le Du, P. Leblanc, A. M. Lee, M. H. Lehto, D. Lellouch, P. Lennert, C. Leroy, L. Lessard, S. Levegrün, L. Levinson, S. L. Lloyd, F. K. Loebinger, J. M. Lorah, B. Lorazo, M. J. Losty, X. C. Lou, J. Ludwig, M. Mannelli, S. Marcellini, G. Maringer, A. J. Martin, J. P. Martin, T. Mashimo, P. Mättig, U. Maur, T. J. McMahon, J. R. McNutt, F. Meijers, D. Menszner, F. S. Merritt, H. Mes, A. Michelini, R. P. Middleton, G. Mikenberg, J. Mildenberger, D. J. Miller, C. Milstene, R. Mir, W. Mohr, C. Moisan, A. Montanari, T. Mori, M. W. Moss, T. Mouthuy, P. G. Murphy, B. Nellen, H. H. Nguyen, M. Nozaki, S. W. O'Neale, B. P. O'Neill, F. G. Oakham, F. Odorici, M. Ogg, H. O. Ogren, H. Oh, C. J. Oram, M. J. Oreglia, S. Orito, J. P. Pansart, B. Panzer-Steindel, P. Paschievici, G. N. Patrick, S. J. Pawley, P. Pfister, J. E. Pilcher, J. L. Pinfold, D. E. Plane, P. Poffenberger, B. Poli, A. Pouladdej, E. Prebys, T. W. Pritchard, H. Przysiezniak, G. Quast, M. W. Redmond, D. L. Rees, K. Riles, S. A. Robins, D. Robinson, A. Rollnik, J. M. Roney, S. Rossberg, A. M. Rossi, P. Routenburg, K. Runge, O. Runolfsson, D. R. Rust, S. Sanghera, M. Sasaki, A. D. Schaile, O. Schaile, W. Schappert, P. Scharff-Hansen, P. Schenk, H. von der Schmitt, S. Schreiber, J. Schwarz, W. G. Scott, M. Settles, B. C. Shen, P. Sherwood, R. Shypit, A. Simon, P. Singh, G. P. Siroli, A. Skuja, A. M. Smith, T. J. Smith, G. A. Snow, R. Sobie, R. W. Springer, M. Sproston, K. Stephens, H. E. Stier, D. Strom, H. Takeda, T. Takeshita, P. Taras, S. Tarem, P. Teixeira-Dias, N. J. Thackray, T. Tsukamoto, M. F. Turner, G. Tysarczyk-Niemeyer, D. Van den plas, R. Van Kooten, G. J. VanDalen, G. Vasseur, C. J. Virtue, A. Wagner, C. Wahl, J. P. Walker, C. P. Ward, D. R. Ward, P. M. Watkins, A. T. Watson, N. K. Watson, M. Weber, S. Weisz, P. S. Wells, N. Wermes, M. Weymann, M. A. Whalley, G. W. Wilson, J. A. Wilson, I. Wingerter, V. H. Winterer, N. C. Wood, S. Wotton, T. R. Wyatt, R. Yaari, Y. Yang, G. Yekutieli, I. Zacharov, W. Zeuner, G. T. Zorn

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Abstract

From a sample of 3308 e+e- → τ+τ- events with an estimated background of 1.9%, we find 964 τ → eνν, 903 τ → μνν, and 309 τ → π(K)ν candidates. Efficiency and background estimates determined from both Monte Carlo and control sample studies yield the following branching ratios: B(τ → eνν) = 17.4 ± 0.5 (stat) ± 0.4 (sys)%, B(τ → μνν) = 16.8 ± 0.5 ± 0.4%, and B(τ → π(K)ν) = 12.1 ± 0.7 ± 0.5%. These values are in good agreement with previous measurements. The measured lepton branching ratios, when combined with the world-average measured value for the τ lifetime, yield a ratio of the τ Fermi coupling constant to that of the lighter leptons given by Gτ/Ge,μ = 0.92 ± 0.04, where it is assumed Ge = Gμ ≡ Ge,μ. The average τ polarization at the Z° resonance is measured to be -0.01±0.09 from an analysis of the momentum spectra of the electron, muon, and pion candidates, implying that the ratio of vector to axial vector couplings of the τ to the Z° is νττ = 0.01 ± 0.04. The measurements of the average polarizations in the forward and backward hemispheres lead to the efficiency-corrected, forward-backward polarization asymmetry AFBpol = -0.22 ± 0.10, implying for the electron couplings to the Z° the ratio νee = 0.15±0.07. Since these values for the tau and electron couplings are consistent with one another, we assume lepton universality to derive ν/α = 0.05 ± 0.04 and a value for the weak mixing angle of sin2θW = 0.237 ± 0.009, with no ambiguity introduced by the relative signs of ν and α.

Original languageEnglish
Pages (from-to)201-217
Number of pages17
JournalPhysics Letters B
Volume266
Issue number1-2
DOIs
Publication statusPublished - Aug 22 1991
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics

Cite this

Alexander, G., Allison, J., Allport, P. P., Anderson, K. J., Arcelli, S., Armitage, J. C., ... Zorn, G. T. (1991). Measurement of branching ratios and τ polarization from τ→eνν-,τ→μνν-,andτ→π(K)ν decays at LEP. Physics Letters B, 266(1-2), 201-217. https://doi.org/10.1016/0370-2693(91)90768-L