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LIGHT UNFLAVORED MESONS ($\mathit S$ = $\mathit C$ = $\mathit B$ = 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   JSON  (beta) PDGID: S008

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

We have omitted some results that have been superseded by later experiments.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 Semileptonic Kaon (${{\mathit K}}_{{{\mathit \ell}}3}$), Radiative Pion (${{\mathit \pi}}_{ {{\mathit \ell}}2 {{\mathit \gamma}} }$) and Kaon (${{\mathit K}}_{ {{\mathit \ell}}2 {{\mathit \gamma}} }$) Decays

${{\mathit \pi}^{\pm}}$ MASS   $139.57039 \pm0.00018$ MeV (S = 1.8)

${\mathit m}_{{{\mathit \pi}^{+}}}–{\mathit m}_{{{\mathit \mu}^{+}}}$

$({\mathit m}_{{{\mathit \pi}^{+}}}–{\mathit m}_{{{\mathit \pi}^{-}}})/{\mathit m}_{\mathrm {average}}$   $(2 \pm5) \times 10^{-4}$

${{\mathit \pi}^{\pm}}$ 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${}^{3}$

${{\mathit \pi}^{+}}$ $-$ POLARIZATION OF EMITTED ${{\mathit \mu}^{+}}$

${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}}$

${{\mathit \pi}^{\pm}}$ 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

${{\mathit \pi}^{+}}$ 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.
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   $\Gamma_{7}$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$   $<9\times 10^{-6}$ CL=90% 30   $\Gamma_{8}$ ${{\mathit e}^{+}}{{\mathit \nu}_{{e}}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$   $<1.6\times 10^{-7}$ CL=90% 70   ▸ Lepton Family number ($\mathit LF$) or Lepton number ($\mathit L$) violating modes
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