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Measurement of the energy spectrum of ν_e from muon decay and implications for the Lorentz structure of the weak interaction

KARMEN group·B. Armbruster·I. M. Blair·B. A. Bodmann·N. E. Booth·G. Drexlin·V. Eberhard·J. A. Edgington·C. Eichner·K. Eitel·E. Finckh·H. Gemmeke·J. Hößl·T. Jannakos·P. Jünger·M. Kleifges·J. Kleinfeller·W. Kretschmer·R. Maschuw·C. Oehler·P. Plischke·J. Rapp·C. Ruf·M. Steidl·O. Stumm·J. Wolf·B. Zeitnitz
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Abstract

The KARMEN experiment uses the reaction 12C(ν_e,e-)12N to measure the energy distribution of ν_e emitted in muon decay at rest. The ν_e analog ω_l of the famous Michel parameter ρhas been derived from a maximum-likelihood analysis of events near the kinematic end point, E_max. The result, ω_l = (2.7^{+3.8}_{-3.3}\pm 3.1) * 10^{-2}, is in good agreement with the standard model prediction ω_l= 0. We deduce a 90% confidence upper limit of ω_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.

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KARMEN group, B. Armbruster, I. M. Blair, B. A. Bodmann, N. E. Booth, G. Drexlin, V. Eberhard, J. A. Edgington, C. Eichner, K. Eitel, E. Finckh, H. Gemmeke, J. Hößl, T. Jannakos, P. Jünger, M. Kleifges, J. Kleinfeller, W. Kretschmer, R. Maschuw, C. Oehler, P. Plischke, J. Rapp, C. Ruf, M. Steidl, O. Stumm, J. Wolf, B. Zeitnitz. 1998-06-24. Measurement of the energy spectrum of ν_e from muon decay and implications for the Lorentz structure of the weak interaction. https://doi.org/10.1103/physrevlett.81.520

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