Precision measurement of the muon decay parameters rho and delta Academic Article uri icon


  • The TWIST Collaboration has performed new measurements of two of the parameters that describe muon decay: , which governs the shape of the overall momentum spectrum, and , which governs the momentum dependence of the parity-violating decay asymmetry. This analysis gives the results =0.750140.00017(stat)0.00044(syst)0.00011(), where the last uncertainty arises from the correlation between and the decay parameter , and =0.750670.00030(stat)0. 00067(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 of 0.99524

published proceedings


author list (cited authors)

  • MacDonald, R. P., Bayes, R., Bueno, J., Davydov, Y. I., Depommier, P., Faszer, W., ... Tribble, R. E.

citation count

  • 22

complete list of authors

  • MacDonald, RP||Bayes, R||Bueno, J||Davydov, Yu I||Depommier, P||Faszer, W||Fujiwara, MC||Gagliardi, CA||Gaponenko, A||Gill, DR||Grossheim, A||Gumplinger, P||Hasinoff, MD||Henderson, RS||Hillairet, A||Hu, J||Jamieson, B||Kitching, P||Koetke, DD||Marshall, GM||Mathie, EL||Mischke, RE||Musser, JR||Nozar, M||Olchanski, K||Olin, A||Openshaw, R||Poutissou, J-M||Poutissou, R||Quraan, MA||Selivanov, V||Sheffer, G||Shin, B||Stanislaus, TDS||Tacik, R||Tribble, RE

publication date

  • August 2008