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

${{\mathit e}^{-}}$ ASYMMETRY PARAMETER $\mathit A$ INSPIRE search

This is the neutron-spin electron-momentum correlation coefficient. The coefficient itself is not well defined in any measurement once higher-order radiative and recoil corrections, which are experiment dependent, are included. By contrast, measurements of the ratio $\lambda {}\equiv\mathit g_{A}/\mathit g_{V}$ (see data block above) incorporate such higher-order effects. For this reason, and in order to meaningfully compare results from different measurements, we list here the zero-recoil-order A-coefficient, which in the Standard Model and at zero recoil order, is related to $\lambda {}\equiv\mathit g_{A}/\mathit g_{V}$ by $\mathit A$ = $-2$ $\lambda $ ($\lambda $ + 1) $/$ (1 + 3$\lambda {}^{2}$); this assumes that $\mathit g_{A}$ and $\mathit g_{V}$ are real. See e.g. MAERKISCH 2019 and BROWN 2018.
S017BA
VALUE DOCUMENT ID TECN  COMMENT
$\bf{ -0.11958 \pm0.00021}$ OUR AVERAGE  Error includes scale factor of 1.2.
$-0.11985$ $\pm0.00017$ $\pm0.00012$ 1
MAERKISCH
2019
SPEC pulsed cold ${{\mathit n}}$, polarized
$-0.12015$ $\pm0.00034$ $\pm0.00063$ 2
BROWN
2018
UCNA Ultracold ${{\mathit n}}$, polarized
$-0.11926$ $\pm0.00031$ ${}^{+0.00036}_{-0.00042}$ 3
MUND
2013
SPEC Cold ${{\mathit n}}$, polarized
$-0.1160$ $\pm0.0009$ $\pm0.0012$
LIAUD
1997
TPC Cold ${{\mathit n}}$, polarized
$-0.1135$ $\pm0.0014$ 4
YEROZOLIMSKY
1997
CNTR Cold ${{\mathit n}}$, polarized
$-0.1146$ $\pm0.0019$
BOPP
1986
SPEC Cold ${{\mathit n}}$, polarized
• • • We do not use the following data for averages, fits, limits, etc. • • •
$-0.11972$ $\pm0.00025$ 5
SAUL
2020
SPEC Cold ${{\mathit n}}$, polarized
$-0.11952$ $\pm0.00110$ 6
MENDENHALL
2013
UCNA See BROWN 2018
$-0.11966$ $\pm0.00089$ ${}^{+0.00123}_{-0.00140}$ 7
PLASTER
2012
UCNA See MENDENHALL 2013
$-0.11966$ $\pm0.00089$ ${}^{+0.00123}_{-0.00140}$
LIU
2010
UCNA See PLASTER 2012
$-0.1138$ $\pm0.0046$ $\pm0.0021$
PATTIE
2009
SPEC Ultracold ${{\mathit n}}$, polarized
$-0.1189$ $\pm0.0007$ 8
ABELE
2002
SPEC See MUND 2013
$-0.1168$ $\pm0.0017$ 9
MOSTOVOI
2001
CNTR Inferred
$-0.1189$ $\pm0.0012$
ABELE
1997D
 SPEC Cold ${{\mathit n}}$, polarized
$-0.1160$ $\pm0.0009$ $\pm0.0011$
SCHRECKENBACH
1995
TPC See LIAUD 1997
$-0.1116$ $\pm0.0014$
EROZOLIMSKII
1991
CNTR See YEROZOLIMSKY 1997
$-0.114$ $\pm0.005$ 10
EROZOLIMSKII
1979
CNTR Cold ${{\mathit n}}$, polarized
$-0.113$ $\pm0.006$ 10
KROHN
1975
CNTR Cold ${{\mathit n}}$, polarized
1  MAERKISCH 2019 further derive a value for the CKM-element $\vert {{\mathit V}_{{{ud}}}}\vert $ = $0.97351$ $\pm0.00060$, using ${\mathit \tau}_{{{\mathit n}}}$ = 879.7(8) sec and the relation from CZARNECKI 2018.
2  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).
3  This MUND 2013 value includes earlier PERKEO II measurements (ABELE 2002 and ABELE 1997D), with a correction to those results.
4  YEROZOLIMSKY 1997 makes a correction to the EROZOLIMSKII 1991 value.
5  Under the SM assumption that the Fierz term ${{\mathit b}}$ = 0, SAUL 2020 obtain the quoted asymmetry parameter ${{\mathit A}}$ and $\lambda $ = $-1.27607$ $\pm0.00068$. In a combined fit authors extract the values ${{\mathit A}}$ = $-0.1209$ $\pm0.0015$, $\lambda $ = $-1.2792$ $\pm0.0060$, and ${{\mathit b}}$ = $0.017$ $\pm0.021$.
6  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.
7  This PLASTER 2012 value is identical with that given in LIU 2010, but the experiment is now described in detail.
8  This is the combined result of ABELE 2002 and ABELE 1997D.
9  MOSTOVOI 2001 calculates this from its measurement of $\lambda =\mathit g_{\mathit A}/\mathit g_{\mathit V}$ above.
10  These results are not corrected for radiative effects and weak magnetism, but the corrections are small compared to the errors.

           ${{\mathit e}^{-}}$ asymmetry parameter $\mathit A$
  References:
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
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
PATTIE 2009
PRL 102 012301 First Measurement of the Neutron $\beta $ Asymmetry with Ultracold Neutrons
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
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
KROHN 1975
PL 55B 175 $\mathit G_{A}/G_{V}$ Measured in the Decay of Polarized Neutrons