${{\mathit n}}$ $\rightarrow$ ${{\mathit p}}{{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}$ DECAY PARAMETERS

See the above “Note on Baryon Decay Parameters.” For discussions of recent results, see the references cited at the beginning of the section on the neutron mean life. For discussions of the values of the weak coupling constants ${\mathit g}_{{{\mathit A}}}$ and ${\mathit g}_{{{\mathit V}}}$ obtained using the neutron lifetime and asymmetry parameter$~\mathit A$, comparisons with other methods of obtaining these constants, and implications for particle physics and for astrophysics, see DUBBERS 1991 and WOOLCOCK 1991. For tests of the $\mathit V−\mathit A$ theory of neutron decay, see EROZOLIMSKII 1991B, MOSTOVOI 1996, NICO 2005, SEVERIJNS 2006, and ABELE 2008.

${{\mathit e}}-{{\overline{\mathit \nu}}_{{{e}}}}$ ANGULAR CORRELATION COEFFICIENT $\mathit a$

INSPIRE   PDGID:
S017BNC
For a review of past experiments and plans for future measurements of the $\mathit a$ parameter, see WIETFELDT 2005. In the Standard Model, $\mathit a$ is related to $\lambda {}\equiv\mathit g_{A}/\mathit g_{V}$ by $\mathit a$ = (1 $−$ $\lambda {}^{2}$) $/$ (1 + 3$\lambda {}^{2}$); this assumes that $\mathit g_{A}$ and $\mathit g_{V}$ are real.
VALUE DOCUMENT ID TECN  COMMENT
$\bf{ -0.1049 \pm0.0013}$ OUR AVERAGE  Error includes scale factor of 1.8.
$-0.10782$ $\pm0.00124$ $\pm0.00133$ 1
HASSAN
2021
SPEC Proton recoil spectrum
$-0.10430$ $\pm0.00084$
BECK
2020
SPEC Proton recoil spectrum
$-0.1054$ $\pm0.0055$
BYRNE
2002
SPEC Proton recoil spectrum
$-0.1017$ $\pm0.0051$
STRATOWA
1978
CNTR Proton recoil spectrum
$-0.091$ $\pm0.039$
GRIGOREV
1968
SPEC Proton recoil spectrum
• • We do not use the following data for averages, fits, limits, etc. • •
$-0.1090$ $\pm0.0030$ $\pm0.0028$ 2
DARIUS
2017
SPEC Cold ${{\mathit n}}$, unpolarized
$-0.1045$ $\pm0.0014$ 3
MOSTOVOI
2001
CNTR Inferred
1  The result of HASSAN 2021 includes the data of DARIUS 2017, and thus supersedes those entries. HASSAN 2021 uses the asymmetry in time-of-flight between the beta electron and recoil proton in delayed coincidence.
2  DARIUS 2017 exploits a "wishbone" correlation, where the ${{\mathit p}}$ time of flight is correlated with the momentum of the electron in delayed coincidence. Data is included in HASSAN 2021.
3  MOSTOVOI 2001 calculates this from its measurement of $\lambda =\mathit g_{\mathit A}/\mathit g_{\mathit V}$ above.
References