#### $\vert (\xi$ PARAMETER)${\times }({{\mathit \mu}}$ LONGITUDINAL POLARIZATION)$\vert$

($\mathit V−\mathit A$) theory predicts $\xi$ = 1, longitudinal polarization = 1.
VALUE DOCUMENT ID TECN CHG  COMMENT
 $\bf{ 1.0009 {}^{+0.0016}_{-0.0007}}$ OUR AVERAGE
$1.00084$ $\pm0.00029$ ${}^{+0.00165}_{-0.00063}$
 2011
TWST Surface ${{\mathit \mu}^{+}}$ beam
$1.0027$ $\pm0.0079$ $\pm0.0030$
 1987
CNTR SIN, ${{\mathit \pi}}$ decay in flight
• • We do not use the following data for averages, fits, limits, etc. • •
$1.0003$ $\pm0.0006$ $\pm0.0038$
 2006
TWST + surface ${{\mathit \mu}^{+}}$ beam
$1.0013$ $\pm0.0030$ $\pm0.0053$ 1
 1992
SPEC + ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}$
$0.975$ $\pm0.015$
 1968
EMUL 140 kG
$0.975$ $\pm0.030$
 1964
EMUL See AKHMANOV 1968
$0.903$ $\pm0.027$ 2
 1961
EMUL + 27 kG
$0.93$ $\pm0.06$
 1960
HBC + 8.8 kG
$0.97$ $\pm0.05$
 1959
CNTR Bromoform target
 1 The corresponding 90$\%$ confidence limit from IMAZATO 1992 is $\vert \xi {{\mathit P}_{{\mu}}}$ $\vert$ $>0.990$. This measurement is of ${{\mathit K}^{+}}$ decay, not ${{\mathit \pi}^{+}}$ decay, so we do not include it in an average, nor do we yet set up a separate data block for ${{\mathit K}}$ results.
 2 Depolarization by medium not known sufficiently well.
References:
 BUENO 2011
PR D84 032005 Precise Measurement of Parity Violation in Polarized Muon Decay
 Also
PR D85 039908 (errat.) Publisher's Note BUENO 2011 : Precise Measurement of Parity Violation in Polarized Muon Decay [Phys. Rev. D 84, 032005 (2011)]
 JAMIESON 2006
PR D74 072007 Measurement of $\mathit P_{{{\mathit \mu}} }{{\mathit \xi}}$ in Polarized Muon Decay
 IMAZATO 1992
PRL 69 877 Search for Right Handed Currents in the Decay Chain ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}}$ , ${{\mathit \mu}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$
 BELTRAMI 1987
PL B194 326 Muon Decay: Measurement of the Integral Asymmetry Parameter
 AKHMANOV 1968
SJNP 6 230 Asymmetry of Positrons from the Decay ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}$ in the Longitudinal 140000 oe Magnetic Field
 GUREVICH 1964
PL 11 185 Asymmetry of the ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}$ Decay $−$ Electron Angular Distribution in a Longitudinal Magnetic Field of 140000 Gauss
 ALI-ZADE 1961
JETP 13 313 Angular Distribution Asymmetry of ${{\mathit \mu}}$ ${{\mathit e}^{-}}$ Decay Electrons in Magnetic Fields up to 35000 Oe
 PLANO 1960
PR 119 1400 Momentum and Asymmetry Spectrum of ${{\mathit \mu}}$ Meson Decay
 BARDON 1959
PRL 2 56 Asymmetry Parameter in Muon Decay