#### $\rho$ PARAMETER

($\mathit V−\mathit A$) theory predicts $\rho$ = 0.75.
VALUE EVTS DOCUMENT ID TECN CHG  COMMENT
 $\bf{ 0.74979 \pm0.00026}$ OUR AVERAGE
$0.74977$ $\pm0.00012$ $\pm0.00023$ 1
 2011
TWST + Surface ${{\mathit \mu}^{+}}$
$0.7518$ $\pm0.0026$
 1969
RVUE
• • We do not use the following data for averages, fits, limits, etc. • •
$0.75014$ $\pm0.00017$ $\pm0.00045$ 2
 2008
TWST + Surface ${{\mathit \mu}^{+}}$
$0.75080$ $\pm0.00032$ $\pm0.00100$ 6G 3
 2005
TWST + Surface ${{\mathit \mu}^{+}}$
$0.72$ $\pm0.06$ $\pm0.08$
 2004
ICAR Liquid Ar TPC
$0.762$ $\pm0.008$ 170k 4
 1968
ASPK + 25$-$53 MeV ${{\mathit e}^{+}}$
$0.760$ $\pm0.009$ 280k 4
 1967
ASPK + 25$-$53 MeV ${{\mathit e}^{+}}$
$0.7503$ $\pm0.0026$ 800k 4
 1966
ASPK + 20$-$53 MeV ${{\mathit e}^{+}}$
 1 The quoted systematic error includes a contribution of 0.00013 (added in quadrature) from uncertainties on radiative corrections and on the Michel parameter $\eta$.
 2 The quoted systematic error includes a contribution of 0.00011 (added in quadrature) from the dependence on the Michel parameter $\eta$.
 3 The quoted systematic error includes a contribution of $0.00023$ (added in quadrature) from the dependence on the Michel parameter $\eta$.
 4 ${{\mathit \eta}}$ constrained = 0. These values incorporated into a two parameter fit to ${{\mathit \rho}}$ and ${{\mathit \eta}}$ by DERENZO 1969 .
References:
 BAYES 2011
PRL 106 041804 Experimental Constraints on Left-Right Symmetric Models from Muon Decay
 Also
PR D85 092013 Precision Muon Decay Measurements and Improved Constraints on the Weak Interaction
 MACDONALD 2008
PR D78 032010 Precision Measurement of the Muon Decay Parameters ${{\mathit \rho}}$ and ${{\mathit \delta}}$
 MUSSER 2005
PRL 94 101805 Measurement of the Michel Parameter ${{\mathit \rho}}$ in Muon Decay
 AMORUSO 2004
EPJ C33 233 Measurement of the ${{\mathit \mu}}$ Decay Spectrum with the ICARUS Liquid Argon TPC
 DERENZO 1969
PR 181 1854 Measurement of the Low Energy End of the ${{\mathit \mu}^{+}}$ Decay Spectrum
 FRYBERGER 1968
PR 166 1379 Measurement of the Muon Decay Spectrum with a Wire Spark Chamber Spectrometer
 SHERWOOD 1967
PR 156 1475 Measurement of the Muon Decay Spectrum with a Wire Spark Chamber Spectrometer
 PEOPLES 1966
Nevis 147 unpub. Positron Spectrum from Muon Decay.