Measurement of the Michel Parameter $\rho$ in Muon Decay

Abstract

The TWIST Collaboration has measured the Michel parameter $\rho$ in normal muon decay, ${\mu }^{+}\to e^{+}{\nu }_e{\bar{\nu }}_{\mu }$. In the Standard Model, $\rho$ = 3/4. Deviations from this value require mixing of left- and right-handed muon and electron couplings in the muon-decay Lagrangian. We find $\rho$ = 0.75080 $\pm$ 0.00044(stat.) $\pm$ 0.00093(syst.) $\pm$ 0.00023, where the last uncertainty represents the dependence of $\rho$ on the Michel parameter $\eta$. This result sets new limits on the $W_L-W_R$ mixing angle in left-right symmetric models.

4 pages, 3 figures, submitted to PRL

References in corpus (7)

• Big Bang Nucleosynthesis (in "The Review of Particle Properties" 2004)
• Muon Decay and Physics Beyond the Standard Model
• O(α^2 \ln(m_μ/m_e)) Corrections to Electron Energy Spectrum in Muon Decay
• Muon Decay Spectrum: Leading Logarithmic Approximation
• Higher order QED corrections to muon decay spectrum
• First Order Radiative Corrections to Polarized Muon Decay Spectrum
• Virtual and Soft Pair Corrections to Polarized Muon Decay Spectrum

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