Abstract
The Crystal Ball detector at the Doris II storage ring at DESY has been used to study the electron energy spectrum of the decay τ→evv̄. In the standard model the Lorentz structure of the decay matrix element is of the well known V-A type, resulting in a Michel parameter of p=0.75. Our spectrum is found to be consistent with this value. A fit yields the value of 0.64±0.07.
Highlights
Since the discovery of the x lepton [1] in e +e-, x+x- [2 ], a large number of groups at various laboratories have investigated its properties [ 3 ]
All evidence available to date supports the validity of the standard model and the treatment of the z lepton as the sequential partner of the muon and electron
The Lorentz structure of the vertices of the above decays is central to the standard model; a deviation from the V-A structure would severely challenge the standard model
Summary
ZSCHORSCHca University of Nijmegen and NIKHEF 3, NL-6525 El) Nijmegen, The Netherlands b Harvard University 4, Cambridge, MA 02138, USA c Deutsches Electronen Synchrotron DESY, D-2000 Hamburg, FRG d Princeton University 5, Princeton, N J 08544, USA e Universitdt Hamburg, I. INFN and University of Firenze, 1-50100 Florence, Italy s High Energy Physics Laboratory, Department of Physics 7 Stanford University, Stanford, CA 94305, USA and Stanford Linear Accelerator Center s, Stanford University, Stanford, CA 94305, USA h Carnegie-Mellon University 9 Pittsburgh, PA 15213, USA i University o f California at Santa Cruz ~o,Santa Cruz, CA 95064, USA J Universitdt Erlangen-Nfirnberg ~, D-8520 Erlangen, FRG k Cracow Institute of Nuclear Physics, PL-30055 Cracow, Poland. Universitdt Wiirzburg ~2,D-8700 Wiirzburg, FRG m California Institute of Technology ~3,Pasadena, CA 91125. Our spectrum is found to be consistent with this value.
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