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${{\mathit \pi}^{\pm}}$ MASS
$139.57061 \pm0.00024$ MeV (S = 1.6)
${\mathit m}_{{{\mathit \pi}^{+}}}{\mathit m}_{{{\mathit \mu}^{+}}}$
$({\mathit m}_{{{\mathit \pi}^{+}}}{\mathit m}_{{{\mathit \pi}^{-}}})/{\mathit m}_{\mathrm {average}}$
$(2 \pm5) \times 10^{-4}$
${{\mathit \pi}^{\pm}}$ MEAN LIFE
$(2.6033 \pm0.0005) \times 10^{-8}$ s (S = 1.2)
$({\mathit \tau}_{{{\mathit \pi}^{+}}}{\mathit \tau}_{{{\mathit \pi}^{-}}})/{\mathit \tau}_{\mathrm {average}}$
$(6 \pm7) \times 10^{-4}$
${{\mathit \pi}}$ ELECTRIC POLARIZABILITY ${{\mathit \alpha}}_{{{\mathit \pi}}}$
$(2.0 \pm0.9) \times 10^{-4}$ fm${}^{3}$
${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}}$
$\mathit F_{\mathit V}$, VECTOR FORM FACTOR
$0.0254 \pm0.0017$
$\mathit F_{\mathit A}$, AXIAL-VECTOR FORM FACTOR
$0.0119 \pm0.0001$
VECTOR FORM FACTOR SLOPE PARAMETER $\mathit a$
$0.10 \pm0.06$
$\mathit R$, SECOND AXIAL-VECTOR FORM FACTOR
$0.059 {}^{+0.009}_{-0.008}$
${{\mathit \pi}^{\pm}}$ CHARGE RADIUS
$0.659 \pm0.004$ fm
${{\mathit \pi}^{-}}$ modes are charge conjugates of the modes below. For decay limits to particles which are not established, see the section on Searches for Axions and Other Very Light Bosons.
Mode
Fraction ($\Gamma_i$ / $\Gamma$)
Scale Factor/ Conf. Level
P (MeV/c)
$\Gamma_{1}$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}$ [1] $(99.98770\pm{0.00004})\%$ 30
$\Gamma_{2}$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}{{\mathit \gamma}}$ [2] $(2.00\pm{0.25})\times 10^{-4}$ 30
$\Gamma_{3}$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}$ [1] $(1.230\pm{0.004})\times 10^{-4}$ 70
$\Gamma_{4}$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit \gamma}}$ [2] $(7.39\pm{0.05})\times 10^{-7}$ 70
$\Gamma_{5}$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit \pi}^{0}}$ $(1.036\pm{0.006})\times 10^{-8}$ 4
$\Gamma_{6}$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ $(3.2\pm{0.5})\times 10^{-9}$ 70
$\Gamma_{7}$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ $<5\times 10^{-6}$ CL=90% 70
▸ Lepton Family number ($\mathit LF$) or Lepton number ($\mathit L$) violating modes