First Measurement of the Michel Parameter?0 in the t- ? μ- ?-μ?t Decay at Belle

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2023-07-11, 2023-07-11

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American Physical Society


We report the first measurement of the Michel parameter ζ′ in the τ-→μ-ν¯μντ decay with a new method proposed just recently. The measurement is based on the reconstruction of the τ-→μ-ν¯μντ events with subsequent muon decay in flight in the Belle central drift chamber. The analyzed data sample of 988 fb-1 collected by the Belle detector corresponds to approximately 912×106 τ+τ- pairs. We measure ζ′=0.22±0.94(stat)±0.42(syst), which is in agreement with the standard model prediction of ζ′=1. Statistical uncertainty dominates in this study, being a limiting factor, while systematic uncertainty is well under control. Our analysis proved the practicability of this promising method and its prospects for further precise measurement in future experiments.



Science & Technology, Physical Sciences, Physics, Multidisciplinary, Physics, Belle Collaboration, 5106 Nuclear and Plasma Physics, 5107 Particle and High Energy Physics, 5110 Synchrotrons and Accelerators, 51 Physical Sciences, 40 Engineering, 49 Mathematical sciences