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We have omitted some results that have been superseded by later experiments.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

Decay Modes ▸ Expand all decays

${{\mathit \pi}^{-}}$ 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.