# ${{\boldsymbol n}}$ $\rightarrow$ ${{\boldsymbol p}}{{\boldsymbol e}^{-}}{{\overline{\boldsymbol \nu}}_{{e}}}$ 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 .

# ${{\boldsymbol e}}-{{\overline{\boldsymbol \nu}}_{{e}}}$ ANGULAR CORRELATION COEFFICIENT $\boldsymbol a$ INSPIRE search

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
$\bf{ -0.1059 \pm0.0028}$ OUR AVERAGE
$-0.1090$ $\pm0.0030$ $\pm0.0028$ 1
 2017
SPEC Cold ${{\mathit n}}$, unpolarized
$-0.1054$ $\pm0.0055$
 2002
SPEC Proton recoil spectrum
$-0.1017$ $\pm0.0051$
 1978
CNTR Proton recoil spectrum
$-0.091$ $\pm0.039$
 1968
SPEC Proton recoil spectrum
• • • We do not use the following data for averages, fits, limits, etc. • • •
$-0.1045$ $\pm0.0014$ 2
 2001
CNTR Inferred
1  DARIUS 2017 exploits a "wishbone" correlation, where the ${{\mathit p}}$ time of flight is correlated with the momentum of the electron in delayed coincidence.
2  MOSTOVOI 2001 calculates this from its measurement of $\lambda =\mathit g_{\mathit A}/\mathit g_{\mathit V}$ above.
References:
 DARIUS 2017
PRL 119 042502 Measurement of the Electron-Antineutrino Angular Correlation in Neutron $\beta$ Decay
 BYRNE 2002
JP G28 1325 Determination of the ${{\overline{\mathit \nu}}_{{e}}}$ Angular Correlation Coefficient a$_{0}$ and the Parameter $\vert \Lambda \vert$ = $\vert \mathit G_{A}/G_{V}\vert$ in Free Neutron $\beta$-Decay from Measurements of the Integrated Energy Spectrum of Recoil Protons Stored in an Ion Trap
 MOSTOVOI 2001
PAN 64 1955 Experimental Value of $\mathit G_{a}/G_{v}$ from a Measurement of Both $\mathit P$-odd Correlations in Free-neutron Decay
 STRATOWA 1978
PR D18 3970 Ratio $\vert \mathit g_{A}$/g$_{V}\vert$ Derived from the Proton Spectrum in Free Neutron Decay
 GRIGOREV 1968
SJNP 6 239 Measurement of Angular (${{\mathit e}}$, ${{\overline{\mathit \nu}}_{{e}}}$) Correlation at Free Neutron Decay