# $\eta$ PARAMETER INSPIRE search

($\mathit V−\mathit A$) theory predicts $\eta$ = 0.
VALUE EVTS DOCUMENT ID TECN CHG  COMMENT
$\bf{ 0.057 \pm0.034}$ OUR AVERAGE
$0.071$ $\pm0.037$ $\pm0.005$ 30M
 2005
CNTR + $7 - 53$ MeV ${{\mathit e}^{+}}$
$0.011$ $\pm0.081$ $\pm0.026$ 5.3M 1
 1985 B
CNTR + 9$-$53 MeV ${{\mathit e}^{+}}$
$-0.12$ $\pm0.21$ 6346
 1969
HBC + 1.6$-$6.8 MeV ${{\mathit e}^{+}}$
• • • We do not use the following data for averages, fits, limits, etc. • • •
$-0.0021$ $\pm0.0070$ $\pm0.0010$ 30M 2
 2005
CNTR + $7 - 53$ MeV ${{\mathit e}^{+}}$
$-0.012$ $\pm0.015$ $\pm0.003$ 5.3M 2
 1985 B
CNTR + 9$-$53 MeV ${{\mathit e}^{+}}$
$-0.007$ $\pm0.013$ 5.3M 3
 1985 B
FIT + 9$-$53 MeV ${{\mathit e}^{+}}$
$-0.7$ $\pm0.5$ 170k 4
 1968
ASPK + 25$-$53 MeV ${{\mathit e}^{+}}$
$-0.7$ $\pm0.6$ 280k 4
 1967
ASPK + 25$-$53 MeV ${{\mathit e}^{+}}$
$0.05$ $\pm0.5$ 800k 4
 1966
ASPK + 20$-$53 MeV ${{\mathit e}^{+}}$
$-2.0$ $\pm0.9$ 9213 5
 1960
HBC + Whole spectrum
1  Previously we used the global fit result from BURKARD 1985B in OUR AVERAGE, we now only include their actual measurement.
2  $\alpha$ = $\alpha {{}^\prime}$ = 0 assumed.
3  Global fit to all measured parameters. The fit correlation coefficients are given in BURKARD 1985B.
4  ${{\mathit \rho}}$ constrained = 0.75.
5  Two parameter fit to ${{\mathit \rho}}$ and ${{\mathit \eta}}$; PLANO 1960 discounts value for ${{\mathit \eta}}$.
References:
 DANNEBERG 2005
PRL 94 021802 Muon Decay: Measurement of the Transverse Polarization of the Decay Positrons and its Implications for the Fermi Coupling Constant and Time Reversal Invariance
 BURKARD 1985B
PL 160B 343 Muon Decay: Measurement of the Transverse Positron Polarization and General Analysis
 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.
 PLANO 1960
PR 119 1400 Momentum and Asymmetry Spectrum of ${{\mathit \mu}}$ Meson Decay