MEASUREMENT OF BRANCHING RATIOS AND TAU-POLARIZATION FROM TAU-]E-NU-NU-BAR,TAU-]MU-NU-NU-BAR, AND TAU-]PI(K)NU DECAYS AT LEP

被引：75

作者：

ALEXANDER, G

机构：

[1] Department of Physics and Astronomy, Tel Aviv University, Tel Aviv

[2] Department of Physics, Schuster Laboratory, The University, Manchester

[3] Cavendish Laboratory, Cambridge

[4] Enrico Fermi Institute, Department of Physics, University of Chicago, Chicago

[5] Dipartimento di Fisica dell'Università di Bologna, INFN

[6] Department of Physics, Carleton University, Ottawa, Ont. K1S 5B6, Colonel By Drive

[7] Laboratoire de Physique Nucléaire, Université de Montréal, Montreal

[8] Department of Physics and Astronomy, University of Maryland, College Park

[9] Queen Mary and Westfield College, University of London, London

[10] Fakultät für Physik, Albert Ludwigs Universität

[11] CERN, European Organisation for Particle Physics

[12] Rutherford Appleton Laboratory, Chilton, Didcot

[13] Physikalisches Institut, Universität Heidelberg

[14] Physikalisches Institut, Universität Bonn

[15] School of Physics and Space Research, University of Birmingham, Birmingham

[16] Department of Physics, Indiana University, Bloomington, IN 47405

[17] Brunel University, Uxbridge

[18] University College London, London

[19] Department of Physics, Technion-Israel Institute of Technology, Haifa

[20] Birkbeck College, London

[21] DPhPE, CEN-Saclay

[22] Department of Physics, University of California, Riverside

[23] Centre for Research in Particle Physics, Carleton University, Ottawa

[24] Nuclear Physics Department, Weizmann Institute of Science, Rehovot

[25] International Center for Elementary Particle Physics, Department of Physics, University of Tokyo, Tokyo

[26] Kobe University, Kobe

[27] National Research Council of Canada, Herzberg Institute of Astrophysics, Ottawa

来源：

PHYSICS LETTERS B | 1991年 / 266卷 / 1-2期

关键词：

D O I：

10.1016/0370-2693(91)90768-L

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

From a sample of 3308 e+e- --> tau+tau- events with an estimated background of 1.9%, we find 964 tau --> e-nu-nuBAR, 903 tau --> mu-nu-nuBAR, and 309 tau --> pi (K)nu candidates. Efficiency and background estimates determined from both Monte Carlo and control sample studies yield the following branching ratios: B(tau --> e-nu-nuBAR) = 17.4 +/- 0.5 (stat) +/- 0.4 (sys)%, B(tau --> mu-nu-nuBAR) = 16.8 +/- 0.5 +/- 0.4%, and B(tau --> pi(K)nu) = 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 tau-lifetime, yield a ratio of the tau-Fermi coupling constant to that of the lighter leptons given by G-tau/G(e,mu) = 0.92 +/- 0.04, where it is assumed G(e) = G(e,mu). The average tau-polarization at the Z0 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 tau to the Z0 is upsilon-tau/a-tau = 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 A(pol)FB = -0.22 +/- 0.10, implying for the electron couplings to the Z0 the ratio upsilon-e/a(e) = 0.15 +/- 0.07. Since these values for the tau and electron couplings are consistent with one another, we assume lepton universality to derive upsilon/a = 0.05 +/- 0.04 and a value for the weak mixing angle of sin2theta-WBAR = 0.237 +/- 0.009, with no ambiguity introduced by the relative signs of upsilon and a.

引用

页码：201 / 217

页数：17

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