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

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

In the Standard Model $\lambda {}\equiv\mathit g_{A}/\mathit g_{V}$ is related to parameter $\mathit a$, ${{\mathit e}}-{{\overline{\mathit \nu}}_{{{e}}}}$ angular correlation coefficient, by $\mathit a$ = (1 $−$ $\lambda {}^{2}$) $/$ (1 + 3$\lambda {}^{2}$); this assumes that $\mathit g_{A}$ and $\mathit g_{V}$ are real. The relationship between $\mathit a$ and $\lambda $ is further modified once recoil corrections are included, see WIETFELDT 2024.
S017AV
VALUE DOCUMENT ID TECN  COMMENT
$\bf{ -1.2753 \pm0.0013}$ OUR AVERAGE  Error includes scale factor of 2.7.
$-1.2712$ $\pm0.0061$ 1
WIETFELDT
2024
SPEC Cold ${{\mathit n}}$, unpolarized
$-1.2677$ $\pm0.0028$ 2
BECK
2020
SPEC Proton recoil spectrum
$-1.27641$ $\pm0.00045$ $\pm0.00033$ 3
MAERKISCH
2019
SPEC pulsed cold ${{\mathit n}}$, polarized
$-1.2772$ $\pm0.0020$ 4
BROWN
2018
UCNA Ultracold ${{\mathit n}}$, polarized
$-1.2748$ $\pm0.0008$ ${}^{+0.0010}_{-0.0011}$ 5
MUND
2013
SPEC Cold ${{\mathit n}}$, polarized
$-1.275$ $\pm0.006$ $\pm0.015$
SCHUMANN
2008
CNTR Cold ${{\mathit n}}$, polarized
$-1.2686$ $\pm0.0046$ $\pm0.0007$ 6
MOSTOVOI
2001
CNTR $\mathit A$ and $\mathit B$ ${\times }$ polarizations
$-1.266$ $\pm0.004$
LIAUD
1997
TPC Cold ${{\mathit n}}$, polarized, $\mathit A$
$-1.2594$ $\pm0.0038$ 7
YEROZOLIMSKY
1997
CNTR Cold ${{\mathit n}}$, polarized, $\mathit A$
$-1.262$ $\pm0.005$
BOPP
1986
SPEC Cold ${{\mathit n}}$, polarized, $\mathit A$
• • • We do not use the following data for averages, fits, limits, etc. • • •
$-1.2796$ $\pm0.0062$ 8
HASSAN
2021
SPEC Cold n, unpolarized
$-1.27607$ $\pm0.00068$ 9
SAUL
2020
SPEC Cold ${{\mathit n}}$, polarized, $\mathit A$
$-1.284$ $\pm0.014$ 10
DARIUS
2017
SPEC Cold ${{\mathit n}}$, unpolarized
$-1.2755$ $\pm0.0030$ 11
MENDENHALL
2013
UCNA See BROWN 2018
$-1.27590$ $\pm0.00239$ ${}^{+0.00331}_{-0.00377}$ 12
PLASTER
2012
UCNA See MENDENHALL 2013
$-1.27590$ ${}^{+0.00409}_{-0.00445}$
LIU
2010
UCNA See PLASTER 2012
$-1.2739$ $\pm0.0019$ 13
ABELE
2002
SPEC See MUND 2013
$-1.274$ $\pm0.003$
ABELE
1997D
 SPEC Cold ${{\mathit n}}$, polarized, $\mathit A$
$-1.266$ $\pm0.004$
SCHRECKENBACH
1995
TPC See LIAUD 1997
$-1.2544$ $\pm0.0036$
EROZOLIMSKII
1991
CNTR See YEROZOLIMSKY 1997
$-1.226$ $\pm0.042$
MOSTOVOY
1983
RVUE
$-1.261$ $\pm0.012$
EROZOLIMSKII
1979
CNTR Cold ${{\mathit n}}$, polarized, $\mathit A$
$-1.259$ $\pm0.017$ 14
STRATOWA
1978
CNTR ${{\mathit p}}$ recoil spectrum, $\mathit a$
$-1.263$ $\pm0.015$
EROZOLIMSKII
1977
CNTR See EROZOLIMSKII 1979
$-1.250$ $\pm0.036$ 14
DOBROZEMSKY
1975
CNTR See STRATOWA 1978
$-1.258$ $\pm0.015$ 15
KROHN
1975
CNTR Cold ${{\mathit n}}$, polarized, $\mathit A$
$-1.263$ $\pm0.016$ 16
KROPF
1974
RVUE ${{\mathit n}}$ decay alone
$-1.250$ $\pm0.009$ 16
KROPF
1974
RVUE ${{\mathit n}}$ decay + nuclear ft
1  WIETFELDT 2024 updates HASSAN 2021, see footnote to HASSAN 2021. The value is extracted from the angular correlation coefficient.
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  HASSAN 2021 include earlier data of DARIUS 2017. The value is extracted from the angular correlation coefficient $\mathit a$.
9  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 $ = $-1.2792$ $\pm0.0060$.
10  DARIUS 2017 calculates this value from the measurement of the $\mathit a$ parameter (see below). Data is included in HASSAN 2021.
11  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.
12  This PLASTER 2012 value is identical with that given in LIU 2010, but the experiment is now described in detail.
13  This is the combined result of ABELE 2002 and ABELE 1997D.
14  These experiments measure the absolute value of ${\mathit g}_{{{\mathit A}}}/{\mathit g}_{{{\mathit V}}}$ only.
15  KROHN 1975 includes events of CHRISTENSEN 1970.
16  KROPF 1974 reviews all data through 1972.

           $\lambda {}\equiv{\mathit g}_{{{\mathit A}}}$ $/$ ${\mathit g}_{{{\mathit V}}}$
  References:
WIETFELDT 2024
PR C110 015502 Recoil-Order and Radiative Corrections to the aCORN Experiment
HASSAN 2021
PR C103 045502 Measurement of the neutron decay electron-antineutrino angular correlation by the aCORN experiment
BECK 2020
PR C101 055506 Improved determination of the $\beta$-$\overline{\nu}_e$ angular correlation coefficient $a$ in free neutron decay with the $aSPECT$ spectrometer
SAUL 2020
PRL 125 112501 Limit on the Fierz Interference Term b from a Measurement of the Beta Asymmetry in Neutron Decay
MAERKISCH 2019
PRL 122 242501 Measurement of the Weak Axial-Vector Coupling Constant in the Decay of Free Neutrons Using a Pulsed Cold Neutron Beam
BROWN 2018
PR C97 035505 New result for the neutron $\beta$-asymmetry parameter $A_0$ from UCNA
DARIUS 2017
PRL 119 042502 Measurement of the Electron-Antineutrino Angular Correlation in Neutron $\beta $ Decay
MENDENHALL 2013
PR C87 032501 Precision Measurement of the Neutron Beta-Decay Asymmetry
MUND 2013
PRL 110 172502 Determination of the Weak Axial Vector Coupling $\mathit \lambda $ = $\mathit g_{A}/\mathit g_{V}$ from a Measurement of the ${{\mathit \beta}}$-Asymmetry Parameter $\mathit A$ in Neutron Beta Decay
PLASTER 2012
PR C86 055501 Measurement of the Neutron ${{\mathit \beta}}$-Asymmetry Parameter ${{\mathit A}^{0}}$ with Ultracold Neutrons
LIU 2010
PRL 105 181803 Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons
Also
PRL 105 219903 (errat.) Publisher's Note to LIU 2010: Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons
SCHUMANN 2008
PRL 100 151801 Measurement of the Proton Asymmetry Parameter in Neutron Beta Decay
ABELE 2002
PRL 88 211801 Is the Unitarity of the Quark Mixing CKM Matrix Violated in Neutron $\beta $ Decay?
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
ABELE 1997D
PL B407 212 A Measurement of the $\beta $ Asymmetry $\mathit A$ in the Decay of Free Neutrons
LIAUD 1997
NP A612 53 The Measurement of the $\beta $ Asymmetry in the Decay of Polarized Neutrons
YEROZOLIMSKY 1997
PL B412 240 Corrigendum: Corrected Value of the $\beta $ Emission Asymmetry in the Decay of Polarized Neutrons Measured in 1990
SCHRECKENBACH 1995
PL B349 427 A New Measurements of the $\beta $ Emission Asymmetry in Free Decay of Polarized Neutrons
EROZOLIMSKII 1991
PL B263 33 New Measurement of the Electron Neutron Spin Asymmetry in Neutron $\beta $ Decay
Also
SJNP 52 999 Measurement of the Asymmetry of the Electron Emission with Respect to the Spin Direction of a Decaying Neutron
BOPP 1986
PRL 56 919 The $\beta $ Decay Asymmetry of the Neutron and $\mathit g_{a}$/g$_{v}$
Also
ZPHY C37 179 The $\beta $ Decay Asymmetry of the Neutron
MOSTOVOY 1983
JETPL 37 196 Determination of $\mathit G_{A}/G_{V}$ from the Set of Three Angular Correlation Coefficients Observed in the Decay of the Free Neutron
EROZOLIMSKII 1979
SJNP 30 356 Measurement of the Spin Electron Correlation Coefficient in the Decay of Polarized Neutrons and the Determination of the $\mathit g_{a}$/g$_{v}$ Ratio
STRATOWA 1978
PR D18 3970 Ratio $\vert \mathit g_{A}$/g$_{V}\vert $ Derived from the Proton Spectrum in Free Neutron Decay
EROZOLIMSKII 1977
JETPL 23 663 New Measurements of Spin Electron Angular Correlation in Polarized Neutron Decay
DOBROZEMSKY 1975
PR D11 510 ${{\overline{\mathit \nu}}_{{{e}}}}$ Angular Correlation Coefficient as Measured from Free Neutron Decay
KROHN 1975
PL 55B 175 $\mathit G_{A}/G_{V}$ Measured in the Decay of Polarized Neutrons
KROPF 1974
ZPHY 267 129 Least Squares Adjustment of the Coupling Constants in Nuclear ${{\mathit \beta}}$-Decay
Also
NP A154 160 Least-Squares Adjustment of the Coupling Constants in ${{\mathit \beta}}$-Decay