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

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

INSPIRE   PDGID:
S004XI
($\mathit V−\mathit A$) theory predicts $\xi $ = 1, longitudinal polarization = 1.
VALUE DOCUMENT ID TECN CHG  COMMENT
$\bf{ 1.0009 {}^{+0.0016}_{-0.0007}}$ OUR AVERAGE
$1.00084$ $\pm0.00029$ ${}^{+0.00165}_{-0.00063}$
BUENO
2011
TWST Surface ${{\mathit \mu}^{+}}$ beam
$1.0027$ $\pm0.0079$ $\pm0.0030$
BELTRAMI
1987
CNTR SIN, ${{\mathit \pi}}$ decay in flight
• • We do not use the following data for averages, fits, limits, etc. • •
$1.0003$ $\pm0.0006$ $\pm0.0038$
JAMIESON
2006
TWST + surface ${{\mathit \mu}^{+}}$ beam
$1.0013$ $\pm0.0030$ $\pm0.0053$ 1
IMAZATO
1992
SPEC + ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{{\mu}}}}$
$0.975$ $\pm0.015$
AKHMANOV
1968
EMUL 140 kG
$0.975$ $\pm0.030$
GUREVICH
1964
EMUL See AKHMANOV 1968
$0.903$ $\pm0.027$ 2
ALI-ZADE
1961
EMUL + 27 kG
$0.93$ $\pm0.06$
PLANO
1960
HBC + 8.8 kG
$0.97$ $\pm0.05$
BARDON
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