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LEPTONS

INSPIRE JSON (beta) PDGID:

${{\mathit \mu}}$

$J$ = $1/2$

See related reviews:

Muon Anomalous Magnetic Moment
Muon Decay Parameters

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

$0.1134289259 \pm0.0000000025$ u

${{\mathit \mu}}$ MASS

$105.6583755 \pm0.0000023$ 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 \mu}_{{\mu}}}/({{\mathit e}}\hbar{}/2{{\mathit m}_{{\mu}}})−$1 = (${{\mathit g}_{{\mu}}}−$2)/2

$0.0011659206 \pm0.0000000004$

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

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

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

$<1.8 \times 10^{-19}$ $\mathit e~$cm CL=95.0%

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

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{32}\mathrm {S}$ $\rightarrow$ ${{\mathit e}^{-}}{}^{32}\mathrm {S}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{32}\mathrm {S}$ $\rightarrow$ ${{\mathit \nu}_{{\mu}}}{}^{32}\mathrm {P}^{*}{)}$

$<7 \times 10^{-11}$ CL=90.0%

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Cu}$ $\rightarrow$ ${{\mathit e}^{-}}{}^{}\mathrm {Cu}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Cu}$ $\rightarrow$ capture${)}$

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Ti}$ $\rightarrow$ ${{\mathit e}^{-}}{}^{}\mathrm {Ti}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Ti}$ $\rightarrow$ capture${)}$

$<4.3 \times 10^{-12}$ CL=90.0%

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Pb}$ $\rightarrow$ ${{\mathit e}^{-}}{}^{}\mathrm {Pb}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Pb}$ $\rightarrow$ capture${)}$

$<4.6 \times 10^{-11}$ CL=90.0%

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Au}$ $\rightarrow$ ${{\mathit e}^{-}}{}^{}\mathrm {Au}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Au}$ $\rightarrow$ capture${)}$

$<7 \times 10^{-13}$ CL=90.0%

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

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{32}\mathrm {S}$ $\rightarrow$ ${{\mathit e}^{+}}{}^{32}\mathrm {Si}^{*}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{32}\mathrm {S}$ $\rightarrow$ ${{\mathit \nu}_{{\mu}}}{}^{32}\mathrm {P}^{*}{)}$

$<9 \times 10^{-10}$ CL=90.0%

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{127}\mathrm {I}$ $\rightarrow$ ${{\mathit e}^{+}}{}^{127}\mathrm {Sb}^{*}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{127}\mathrm {I}$ $\rightarrow$ anything${)}$

$<3 \times 10^{-10}$ CL=90.0%

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Cu}$ $\rightarrow$ ${{\mathit e}^{+}}{}^{}\mathrm {Co}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Cu}$ $\rightarrow$ ${{\mathit \nu}_{{\mu}}}{}^{}\mathrm {Ni}{)}$

${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Ti}$ $\rightarrow$ ${{\mathit e}^{+}}{}^{}\mathrm {Ca}{)}$ / ${\mathit \sigma (}$ ${{\mathit \mu}^{-}}$ ${}^{}\mathrm {Ti}$ $\rightarrow$ capture${)}$

$<3.6 \times 10^{-11}$ CL=90.0%

LIMIT ON MUONIUM $\rightarrow$ ANTIMUONIUM CONVERSION

$\mathit R_{\mathit g}$ = $\mathit G_{\mathit C}$ $/$ $\mathit G_{\mathit F}$

$<0.0030$ CL=90.0%

${{\mathit \mu}}$ DECAY PARAMETERS

$\rho $ PARAMETER

$0.74979 \pm0.00026$

$\eta $ PARAMETER

$0.057 \pm0.034$

$\delta $ PARAMETER

$0.75047 \pm0.00034$

$\vert (\xi $ PARAMETER)${\times }({{\mathit \mu}}$ LONGITUDINAL POLARIZATION)$\vert $

$1.0009 {}^{+0.0016}_{-0.0007}$

$\xi $ ${\times }$ (${{\mathit \mu}}$ LONGITUDINAL POLARIZATION) ${\times }$ $\delta $ $/$ $\rho $

$1.0018 {}^{+0.0016}_{-0.0007}$

$\xi {{}^\prime}$ = LONGITUDINAL POLARIZATION OF ${{\mathit e}^{+}}$

$\xi {{}^\prime}{{}^\prime}$ PARAMETER

TRANSVERSE ${{\mathit e}^{+}}$ POLARIZATION IN PLANE OF ${{\mathit \mu}}$ SPIN, ${{\mathit e}^{+}}$ MOMENTUM

$0.007 \pm0.008$

TRANSVERSE ${{\mathit e}^{+}}$ POLARIZATION NORMAL TO PLANE OF ${{\mathit \mu}}$ SPIN, ${{\mathit e}^{+}}$ MOMENTUM

$-0.002 \pm0.008$

$\alpha /\mathit A$

$0.000 \pm0.004$

$\alpha {{}^\prime}/\mathit A$

$-0.010 \pm0.020$

$\beta /\mathit A$

$0.004 \pm0.006$

$\beta {{}^\prime}/\mathit A$

$0.002 \pm0.007$

$\mathit a/\mathit A$

$\mathit a{{}^\prime}/\mathit A$

($\mathit b{{}^\prime}+\mathit b)/\mathit A$

$\mathit c/\mathit A$

$\mathit c{{}^\prime}/\mathit A$

${{\overline{\mathit \eta}}}$ PARAMETER

${{\mathit \mu}^{-}}$ DECAY MODES ▸ Expand all decays

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

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

$\approx{}100\%$

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

$(6.0\pm{0.5})\times 10^{-8}$

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

$(3.4\pm{0.4})\times 10^{-5}$

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

FOOTNOTES

Except where otherwise noted, content of the 2023 Review of Particle Physics is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy), JPS and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2023. See LBNL disclaimers.