Abstract
The decay of the muon has been studied at PSI with several precision measurements: The longitudinal polarization P_{\mathrm{L}}(E)PL(E) with the muon decay parameters \xi'ξ′, \xi''ξ″, the Time-Reversal Invariance (TRI) conserving transverse polarization P_{\mathrm{T_{1}}}(E)PT1(E) with the muon decay parameters \etaη, \eta''η″, the TRI violating transverse polarization P_{\mathrm{T_{2}}}(E)PT2(E), with \alpha'/Aα′/A, \beta'/Aβ′/A and the muon decay asymmetry with P_{\mu}\xiPμξ. The detailed theoretical analysis of all measurements of normal and inverse muon decay has led for the first time to a lower limit |g^{V}_{LL}| > 0.960|gLLV|>0.960 (“V-AV−A”) and upper limits for nine other possible complex couplings, especially the scalar coupling |g^{S}_{LL}| < 0.550|gLLS|<0.550 which had not been excluded before.
Highlights
Muon decay, μ+ → νμe+νe, as a purely leptonic process, provides a precise source of information on the charged current weak interaction
The ETH-SIN group has performed decisive precision measurements and, simultaneously, developed the theoretical description in a way that allowed the determination of the interaction from experimental results, taken exclusively from normal and inverse muon decay
The contact interaction allows the use of equivalent Hamiltonians, which differ in the way the fermions are grouped together [1, 2]
Summary
Μ+ → νμe+νe, as a purely leptonic process, provides a precise source of information on the charged current weak interaction. Before the advent of the meson factories LAMPF, TRIUMF and SIN, experimental results were scarce and theoretical descriptions inappropriate to uniquely deduce the interaction. The ETH-SIN group has performed decisive precision measurements and, simultaneously, developed the theoretical description in a way that allowed the determination of the interaction from experimental results, taken exclusively from normal and inverse muon decay (νμ + e− → μ− + νe)
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