# Measuring the Michel parameter ${x}$'' in polarized muon decay

Abstract : The study of pure leptonic electroweak processes, such as muon decay, is appropriate to test the Standard Model of the electroweak interactions as well as some of its extensions since the radiative corrections are negligible (and understood) at this level of precision. Unlike most of the Michel parameters used to describe muon decay, the uncertainty on the experimental value of xi[double-prime] that fits the Standard Model V-A interaction, is large (xi[double-prime]=0.65±0.36) [1]. In order to improve the accuracy of this value, we have measured the longitudinal polarization, PL, of positrons emitted in the decay of polarized muons as a function of the positron energy. In fact, the value of PL, at the positron endpoint energy equal to unity in the Standard Model, decreases for high energy positrons emitted antiparallel to the muon spin if the combination of Michel parameters xi[double-prime]/xixi[prime]-1 deviates from the Standard Model value, i.e. from zero. We plan to improve the precision on xi[double-prime] to 0.5%. Preliminary results are described.
Document type :
Conference papers

http://hal.in2p3.fr/in2p3-00132360
Contributor : Sandrine Guesnon <>
Submitted on : Wednesday, February 21, 2007 - 11:13:52 AM
Last modification on : Tuesday, February 5, 2019 - 12:12:09 PM

### Citation

X. Morelle, N. Danneberg, J. Deutsch, J. Egger, W. Fetscher, et al.. Measuring the Michel parameter ${x}$'' in polarized muon decay. The fourteenth international spin physics symposium, SPIN2000, 2000, Osaka, Japan. pp.371-378, ⟨10.1063/1.1384084⟩. ⟨in2p3-00132360⟩

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