학술논문
A Precision Measurement of the Muon Decay Parameters $\rho$ and $\delta$
Document Type
Working Paper
Author
TWIST Collaboration; MacDonald, R. P.; Bayes, R.; Bueno, J.; Davydov, Yu. I.; Depommier, P.; Faszer, W.; Fujiwara, M. C.; Gagliardi, C. A.; Gaponenko, A.; Gill, D. R.; Grossheim, A.; Gumplinger, P.; Hasinoff, M. D.; Henderson, R. S.; Hillairet, A.; Hu, J.; Jamieson, B.; Kitching, P.; Koetke, D. D.; Marshall, G. M.; Mathie, E. L.; Mischke, R. E.; Musser, J. R.; Nozar, M.; Olchanski, K.; Olin, A.; Openshaw, R.; Poutissou, J. -M.; Poutissou, R.; Quraan, M. A.; Selivanov, V.; Sheffer, G.; Shin, B.; Stanislaus, T. D. S.; Tacik, R.; Tribble, R. E.
Source
Phys.Rev.D78:032010,2008
Subject
Language
Abstract
The TWIST collaboration has performed new measurements of two of the parameters that describe muon decay: $\rho$, which governs the shape of the overall momentum spectrum, and $\delta$, which governs the momentum dependence of the parity-violating decay asymmetry. This analysis gives the results $\rho=0.75014\pm 0.00017(\text{stat})\pm 0.00044(\text{syst})\pm 0.00011(\eta)$, where the last uncertainty arises from the correlation between $\rho$ and the decay parameter $\eta$, and $\delta = 0.75067\pm 0.00030(\text{stat})\pm 0.00067(\text{syst})$. These are consistent with the value of 3/4 given for both parameters in the Standard Model of particle physics, and are a factor of two more precise than the measurements previously published by TWIST. A new global analysis of all available muon decay data incorporating these results is presented. Improved lower and upper limits on the decay parameter $P_\mu^\pi\xi$ of $0.99524 < P_\mu^\pi\xi \leq \xi < 1.00091$ at 90% confidence are determined, where $P_\mu^\pi$ is the polarization of the muon when it is created during pion decay, and $\xi$ governs the muon decay asymmetry. These results set new model-independent constraints on the possible weak interactions of right-handed particles. Specific implications for left-right symmetric models are discussed.
Comment: 14 pages, 14 figs, accepted for publication in Phys. Rev. D
Comment: 14 pages, 14 figs, accepted for publication in Phys. Rev. D