${{\boldsymbol \mu}}$ DECAY PARAMETERS

$\rho $ PARAMETER INSPIRE search

($\mathit V−\mathit A$) 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
BAYES
2011
TWST + Surface ${{\mathit \mu}^{+}}$
$0.7518$ $\pm0.0026$
DERENZO
1969
RVUE
• • • We do not use the following data for averages, fits, limits, etc. • • •
$0.75014$ $\pm0.00017$ $\pm0.00045$ 2
MACDONALD
2008
TWST + Surface ${{\mathit \mu}^{+}}$
$0.75080$ $\pm0.00032$ $\pm0.00100$ 6G 3
MUSSER
2005
TWST + Surface ${{\mathit \mu}^{+}}$
$0.72$ $\pm0.06$ $\pm0.08$
AMORUSO
2004
ICAR Liquid Ar TPC
$0.762$ $\pm0.008$ 170k 4
FRYBERGER
1968
ASPK + 25$-$53 MeV ${{\mathit e}^{+}}$
$0.760$ $\pm0.009$ 280k 4
SHERWOOD
1967
ASPK + 25$-$53 MeV ${{\mathit e}^{+}}$
$0.7503$ $\pm0.0026$ 800k 4
PEOPLES
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
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.