${{\mathit \mu}}$ DECAY PARAMETERS

$\delta $ PARAMETER

INSPIRE   JSON  (beta) PDGID:
S004DEL
($\mathit V−\mathit A$) theory predicts $\delta $ = 0.75.
VALUE EVTS DOCUMENT ID TECN CHG  COMMENT
$\bf{ 0.75047 \pm0.00034}$ OUR AVERAGE
$0.75049$ $\pm0.00021$ $\pm0.00027$ 1
BAYES
2011
TWST + Surface ${{\mathit \mu}^{+}}$
$0.7486$ $\pm0.0026$ $\pm0.0028$ 2
BALKE
1988
SPEC + Surface ${{\mathit \mu}^{+}}$
• • We do not use the following data for averages, fits, limits, etc. • •
$0.75067$ $\pm0.00030$ $\pm0.00067$
MACDONALD
2008
TWST + Surface ${{\mathit \mu}^{+}}$
$0.74964$ $\pm0.00066$ $\pm0.00112$ 6G
GAPONENKO
2005
TWST + Surface ${{\mathit \mu}^{+}}$
3
VOSSLER
1969
$0.752$ $\pm0.009$ 490k
FRYBERGER
1968
ASPK + 25$-$53 MeV ${{\mathit e}^{+}}$
$0.782$ $\pm0.031$
KRUGER
1961
$0.78$ $\pm0.05$ 8354
PLANO
1960
HBC + Whole spectrum
1  The quoted systematic error includes a contribution of 0.00006 (added in quadrature) from uncertainties on radiative corrections and on the Michel parameter $\eta $.
2  BALKE 1988 uses $\rho $ = $0.752$ $\pm0.003$.
3  VOSSLER 1969 has measured the asymmetry below 10 MeV. See comments about radiative corrections in VOSSLER 1969.
References