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

$\lambda {}\equiv{\mathit g}_{{{\mathit A}}}$ $/$ ${\mathit g}_{{{\mathit V}}}$

VALUE

DOCUMENT ID

TECN

COMMENT

$\bf{ -1.2754 \pm0.0013}$

OUR AVERAGE Error includes scale factor of 2.7.

See the ideogram below.

$-1.2796$ $\pm0.0062$

SPEC

Proton recoil spectrum

$-1.2677$ $\pm0.0028$

SPEC

Proton recoil spectrum

$-1.27641$ $\pm0.00045$ $\pm0.00033$

SPEC

pulsed cold ${{\mathit n}}$, polarized

$-1.2772$ $\pm0.0020$

UCNA

Ultracold ${{\mathit n}}$, polarized

$-1.2748$ $\pm0.0008$ ${}^{+0.0010}_{-0.0011}$

SPEC

Cold ${{\mathit n}}$, polarized

$-1.275$ $\pm0.006$ $\pm0.015$

CNTR

Cold ${{\mathit n}}$, polarized

$-1.2686$ $\pm0.0046$ $\pm0.0007$

CNTR

$\mathit A$ and $\mathit B$ ${\times }$ polarizations

$-1.266$ $\pm0.004$

TPC

Cold ${{\mathit n}}$, polarized, $\mathit A$

$-1.2594$ $\pm0.0038$

CNTR

Cold ${{\mathit n}}$, polarized, $\mathit A$

$-1.262$ $\pm0.005$

SPEC

Cold ${{\mathit n}}$, polarized, $\mathit A$

• • We do not use the following data for averages, fits, limits, etc. • •

$-1.27607$ $\pm0.00068$

SPEC

Cold ${{\mathit n}}$, polarized, $\mathit A$

$-1.284$ $\pm0.014$

SPEC

Cold ${{\mathit n}}$, unpolarized

$-1.2755$ $\pm0.0030$

UCNA

$-1.27590$ $\pm0.00239$ ${}^{+0.00331}_{-0.00377}$

UCNA

See MENDENHALL 2013

$-1.27590$ ${}^{+0.00409}_{-0.00445}$

UCNA

See PLASTER 2012

$-1.2739$ $\pm0.0019$

SPEC

$-1.274$ $\pm0.003$

SPEC

Cold ${{\mathit n}}$, polarized, $\mathit A$

$-1.266$ $\pm0.004$

TPC

$-1.2544$ $\pm0.0036$

CNTR

See YEROZOLIMSKY 1997

$-1.226$ $\pm0.042$

RVUE

$-1.261$ $\pm0.012$

CNTR

Cold ${{\mathit n}}$, polarized, $\mathit A$

$-1.259$ $\pm0.017$

CNTR

${{\mathit p}}$ recoil spectrum, $\mathit a$

$-1.263$ $\pm0.015$

CNTR

See EROZOLIMSKII 1979

$-1.250$ $\pm0.036$

CNTR

See STRATOWA 1978

$-1.258$ $\pm0.015$

CNTR

Cold ${{\mathit n}}$, polarized, $\mathit A$

$-1.263$ $\pm0.016$

RVUE

${{\mathit n}}$ decay alone

$-1.250$ $\pm0.009$

RVUE

${{\mathit n}}$ decay + nuclear ft

¹	HASSAN 2021 include earlier data of DARIUS 2017. The value is extracted from the angular correlation coefficient $\mathit a$.

²	BECK 2020 calculates this value from the measurement of the $\beta $-decay ${{\mathit e}}-{{\overline{\mathit \nu}}_{{{e}}}}$ angular correlation coefficient $\mathit a$.

³	MAERKISCH 2019 gets $\mathit A$ = $-0.11985$ $\pm0.00017$ $\pm0.00012$.

⁴	BROWN 2018 gets $\mathit A$ = $-0.12054$ $\pm0.00044$ $\pm0.00068$ and $\lambda $ = $-1.2783$ $\pm0.0022$. We quote the combined values that include the earlier UCNA measurements (MENDENHALL 2013).

⁵	This MUND 2013 value includes earlier PERKEO II measurements (ABELE 2002 and ABELE 1997D).

⁶	MOSTOVOI 2001 measures the two $\mathit P$-odd correlations $\mathit A$ and $\mathit B$, or rather $\mathit SA$ and $\mathit SB$, where $\mathit S$ is the ${{\mathit n}}$ polarization, in free neutron decay.

⁷	YEROZOLIMSKY 1997 makes a correction to the EROZOLIMSKII 1991 value.

⁸	SAUL 2020 quote this value of $\lambda $ under the SM assumption of the Fierz term ${{\mathit b}}$ = 0. In a combined fit authors extract a value of $\lambda $ = $-1.2792$ $\pm0.0060$.

⁹	DARIUS 2017 calculates this value from the measurement of the $\mathit a$ parameter (see below). Data is included in HASSAN 2021.

¹⁰	MENDENHALL 2013 gets $\mathit A$ = $-0.11954$ $\pm0.00055$ $\pm0.00098$ and $\lambda $ = $-1.2756$ $\pm0.0030$. We quote the nearly identical values that include the earlier UCNA measurement (PLASTER 2012), with a correction to that result.

¹¹	This PLASTER 2012 value is identical with that given in LIU 2010, but the experiment is now described in detail.

¹²	This is the combined result of ABELE 2002 and ABELE 1997D.

¹³	These experiments measure the absolute value of ${\mathit g}_{{{\mathit A}}}/{\mathit g}_{{{\mathit V}}}$ only.

¹⁴	KROHN 1975 includes events of CHRISTENSEN 1970.

¹⁵	KROPF 1974 reviews all data through 1972.

$\lambda {}\equiv{\mathit g}_{{{\mathit A}}}$ $/$ ${\mathit g}_{{{\mathit V}}}$

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