Measurement of the energy spectrum of \nu_e from muon decay and   implications for the Lorentz structure of the weak interaction
  The KARMEN experiment uses the reaction 12C(\nu_e,e-)12N to measure the energy distribution of \nu_e emitted in muon decay at rest. The \nu_e analog \omega_l of the famous Michel parameter \rho has been derived from a maximum-likelihood analysis of events near the kinematic end point, E_max. The result, \omega_l = (2.7^{+3.8}_{-3.3}\pm 3.1) * 10^{-2}, is in good agreement with the standard model prediction \omega_l= 0. We deduce a 90% confidence upper limit of \omega_l <= 0.113, which corresponds to a limit of |g^S_RL + 2 g^T_RL| <= 0.78 on the interference term between scalar and tensor coupling constants. 
KARMEN group: B. Armbruster, I. M. Blair, B. A. Bodmann, N. E. Booth,   G. Drexlin, V. Eberhard, J. A. Edgington, C. Eichner...