LIGHT UNFLAVORED MESONS
($\boldsymbol S$ = $\boldsymbol C$ = $\boldsymbol B$ = 0)
For $\mathit I = 1$ (${{\mathit \pi}}$, ${{\mathit b}}$, ${{\mathit \rho}}$, ${{\mathit a}}$): ${\mathit {\mathit u}}$ ${\mathit {\overline{\mathit d}}}$, ( ${\mathit {\mathit u}}$ ${\mathit {\overline{\mathit u}}}−$ ${\mathit {\mathit d}}$ ${\mathit {\overline{\mathit d}}})/\sqrt {2 }$, ${\mathit {\mathit d}}$ ${\mathit {\overline{\mathit u}}}$;
for $\mathit I = 0$ (${{\mathit \eta}}$, ${{\mathit \eta}^{\,'}}$, ${{\mathit h}}$, ${{\mathit h}^{\,'}}$, ${{\mathit \omega}}$, ${{\mathit \phi}}$, ${{\mathit f}}$, ${{\mathit f}^{\,'}}$): ${\mathit {\mathit c}}_{{\mathrm {1}}}$( ${{\mathit u}}{{\overline{\mathit u}}}$ $+$ ${{\mathit d}}{{\overline{\mathit d}}}$ ) $+$ ${\mathit {\mathit c}}_{{\mathrm {2}}}$( ${{\mathit s}}{{\overline{\mathit s}}}$ )
INSPIRE search

${{\boldsymbol \pi}^{\pm}}$ $I^G(J^{P})$ = $1^-(0^{-})$ 

We have omitted some results that have been superseded by later experiments. The omitted results may be found in our 1988 edition Physics Letters B204 1 (1988).
See related review:
Form Factors for Radiative Pion and Kaon Decays
${{\mathit \pi}^{\pm}}$ 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${}^{3}$ 
${{\boldsymbol \pi}^{+}}$ $-$ POLARIZATION OF EMITTED ${{\boldsymbol \mu}^{+}}$
${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}}$
${{\boldsymbol \pi}^{\pm}}$ FORM FACTORS
$\mathit F_{\mathit V}$, 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.
$\Gamma_{1}$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}$ [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