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${{\mathit \mu}}$

$J$ = $1/2$

See related reviews:

Muon Anomalous Magnetic Moment
Muon Decay Parameters

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${{\mathit \mu}}$ MASS (atomic mass units u)

$0.1134289259$ $\pm0.0000000025$ u

${{\mathit \mu}}$ MASS ^[1]

$105.6583755$ $\pm0.0000023$ MeV

${{\mathit \mu}}$ MEAN LIFE $\tau $

($2.1969811$ $\pm0.0000022$) $ \times 10^{-6}$ s

${\mathit \tau}_{{{\mathit \mu}^{+}}}/{\mathit \tau}_{{{\mathit \mu}^{-}}}$ MEAN LIFE RATIO

$1.00002$ $\pm0.00008$

$({\mathit \tau}_{{{\mathit \mu}^{+}}}-{\mathit \tau}_{{{\mathit \mu}^{-}}})/{\mathit \tau}_{\mathrm {average}}$

($2$ $\pm8$) $ \times 10^{-5}$

${{\mathit \mu}}/{{\mathit p}}$ MAGNETIC MOMENT RATIO

$3.18334514$ $\pm0.00000007$

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

$({\mathit g}_{{{\mathit \mu}^{+}}}-{\mathit g}_{{{\mathit \mu}^{-}}})/{\mathit g}_{average}$

($-1.1$ $\pm1.2$) $ \times 10^{-9}$

${{\mathit \mu}}$ ELECTRIC DIPOLE MOMENT (d)

$< 1.8$ $\times 10^{-19}$ $\mathit e~$cm CL=95%

MUON-ELECTRON CHARGE RATIO ANOMALY $\mathit q_{{{\mathit \mu}^{+}}}/\mathit q_{{{\mathit e}^{-}}}$ $+$ 1

($1.1$ $\pm2.1$) $ \times 10^{-9}$

▸ LIMIT ON ${{\mathit \mu}^{-}}$ $\rightarrow$ ${{\mathit e}^{-}}$ CONVERSION

▸ LIMIT ON ${{\mathit \mu}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}$ CONVERSION

▸ LIMIT ON MUONIUM $\rightarrow$ ANTIMUONIUM CONVERSION

▸ ${{\mathit \mu}}$ DECAY PARAMETERS

${{\mathit \mu}^{-}}$ DECAY MODES

${{\mathit \mu}^{+}}$ modes are charge conjugates of the modes below.

Mode

Fraction ($\Gamma_i$ / $\Gamma$)

Scale Factor/
Conf. Level

P(MeV/c)

${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}{{\mathit \nu}_{{{\mu}}}}$

${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}{{\mathit \nu}_{{{\mu}}}}{{\mathit \gamma}}$

($6.0$ $\pm0.5$) $ \times 10^{-8}$

${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}{{\mathit \nu}_{{{\mu}}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$

($3.4$ $\pm0.4$) $ \times 10^{-5}$

▸ Lepton Family number ($\mathit LF$) violating modes

[1]	The muon mass is most precisely known in u (unified atomic mass units). The conversion factor to MeV via the factor $931.49432$(28) MeV/u is more uncertain because of the electron charge uncertainty.
[2]	$\mathit P_{{{\mathit \mu}}}$ is the longitudinal polarization of the muon from pion decay. For $\mathit V−\mathit A$ coupling, $\mathit P_{{{\mathit \mu}}}$ = 1 and $\rho $ = $\delta $ = 3/4.
[3]	This only includes events with energy of ${{\mathit e}}>$ 45 MeV and energy of ${{\mathit \gamma}}>$ 40 MeV. Since the ${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}{{\mathit \nu}_{{{\mu}}}}$ and ${{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}{{\mathit \nu}_{{{\mu}}}}{{\mathit \gamma}}$ modes cannot be clearly separated, we regard the latter mode as a subset of the former.
[4]	See the Particle Listings below for the energy limits used in this measurement.
[5]	A test of additive vs. multiplicative lepton family number conservation.

Except where otherwise noted, content of the 2025 Review of Particle Physics is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy) and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2025. See LBNL disclaimers.