${{\mathit \mu}}$ MAGNETIC MOMENT ANOMALY

The parity-violating decay of muons in a storage ring is observed. The difference frequency $\omega _{\mathit a}$ between the muon spin precession and the orbital angular frequency (${{\mathit e}}/{\mathit m}_{{{\mathit \mu}}}\mathit c)\langle{}\mathit B\rangle{}$ is measured, as is the free proton NMR frequency $\omega _{{{\mathit p}}}$, thus determining the ratio $\mathit R=\omega _{\mathit a}/\omega _{{{\mathit p}}}$. Given the magnetic moment ratio $\lambda =\mu _{{{\mathit \mu}}}/\mu _{{{\mathit p}}}$ (from hyperfine structure in muonium), ($\mathit g−$2)/2 = $\mathit R/(\lambda −\mathit R$).

${{\mathit \mu}_{{{\mu}}}}/({{\mathit e}}\hbar{}/2{{\mathit m}_{{{\mu}}}})−$1 = (${{\mathit g}_{{{\mu}}}}−$2)/2

INSPIRE   JSON  (beta) PDGID:
S004MM
S004MM
VALUE ($ 10^{-10} $) DOCUMENT ID TECN CHG  COMMENT
$11659207.15$ $\pm1.45$ 1
AGUILLARD
2025
 
MUG2 $\pm{}$ Combined FNAL and BNL values
• • We do not use the following data for averages, fits, limits, etc. • •
$11659207.05$ $\pm1.48$ 2
AGUILLARD
2025
 
MUG2 + Storage ring
$11659205.5$ $\pm2.4$ 3
AGUILLARD
2023
 
MUG2 + Storage ring
$11659205.9$ $\pm2.2$ 4
AGUILLARD
2023
 
MUG2 $\pm{}$ Combined FNAL and BNL values
$11659204.0$ $\pm5.4$
ABI
2021
 
MUG2 + Storage ring
$11659206.1$ $\pm4.1$ 5
ABI
2021
 
MUG2 $\pm{}$ Combined FNAL and BNL values
$11659208.0$ $\pm5.4$ $\pm3.3$
BENNETT
2006
 
MUG2 $\pm{}$ Average ${{\mathit \mu}^{+}}$ and ${{\mathit \mu}^{-}}$
$11659208$ $\pm6$
BENNETT
2004
 
MUG2 $\pm{}$ Average ${{\mathit \mu}^{+}}$ and ${{\mathit \mu}^{-}}$
$11659214$ $\pm8$ $\pm3$
BENNETT
2004
 
MUG2 - Storage ring
$11659203$ $\pm6$ $\pm5$
BENNETT
2004
 
MUG2 + Storage ring
$11659204$ $\pm7$ $\pm5$
BENNETT
2002
 
MUG2 + Storage ring
$11659202$ $\pm14$ $\pm6$
BROWN
2001
 
MUG2 + Storage ring
$11659191$ $\pm59$
BROWN
2000
 
MUG2 +
$11659100$ $\pm110$ 6
BAILEY
1979
 
CNTR + Storage ring
$11659360$ $\pm120$ 6
BAILEY
1979
 
CNTR - Storage ring
$11659230$ $\pm85$ 6
BAILEY
1979
 
CNTR $\pm{}$ Storage ring
$11620000$ $\pm5000$
CHARPAK
1962
 
CNTR +
1  AGUILLARD 2025 combined their value with the previous independent BNL measurement of BENNETT 2006.
2  AGUILLARD 2025 quote the combined value from all RUNS $1 - 6$ (at 127 ppm precision). For the $2020 - 2023$ data (Runs 4, 5, 6) alone AGUILLARD 2025 measure a value of ($11659207.10$ $\pm1.62$) $ \times 10^{-10}$ (at precision of 139 ppb).
3  This AGUILLARD 2023 value is the combination of all 2018, 2019 and 2020 data, including the ABI 2021 value. The new FNAL 2019 and 2020 data alone combined yield ($11659205.7$ $\pm2.5$) $ \times 10^{-10}$.
4  AGUILLARD 2023 combined their value with the previous independent BNL measurement of BENNETT 2006.
5  ABI 2021 combined their value with the previous independent BNL measurement of BENNETT 2006. ABI 2021 also report that the difference of this combination with the standard model value of ($11659181.0$ $\pm4.3$) $ \times 10^{-10}$ (AOYAMA 2020) has a significance of 4.2 ${{\mathit \sigma}}$.
6  BAILEY 1979 values recalculated by HUGHES 1999 using the COHEN 1987 ${{\mathit \mu}}/{{\mathit p}}$ magnetic moment. The improved MOHR 1999 value does not change the result.
References