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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 PDGID: S009

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

We have omitted some results that have been superseded by later experiments.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

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${{\mathit \pi}^{0}}$ MASS [1] $134.9768$ $\pm0.0005$ MeV (S = 1.1)

${\mathit m}_{{{\mathit \pi}^{\pm}}}-{\mathit m}_{{{\mathit \pi}^{0}}}$ $4.5936$ $\pm0.0005$ MeV

${{\mathit \pi}^{0}}$ MEAN LIFE ($8.43$ $\pm0.13$) $ \times 10^{-17}$ s (S = 1.2)

▸  exp ${{\mathit \pi}^{0}}$ ELECTROMAGNETIC FORM FACTOR

LINEAR COEFFICIENT OF ${{\mathit \pi}^{0}}$ ELECTROMAGNETIC FORM FACTOR $0.0335$ $\pm0.0031$

${{\mathit \pi}^{0}}$ DECAY MODES
For decay limits to particles which are not established, see the appropriate Search sections (${{\mathit A}^{0}}$ (axion) and Other Light Boson (${{\mathit X}^{0}}$) Searches, etc.).
Mode   Fraction ($\Gamma_i$ / $\Gamma$) Scale Factor/ Conf. Level P(MeV/c)   $\Gamma_{1}$ 2 ${{\mathit \gamma}}$ ($98.823$ $\pm0.034$ ) $\%$ S=1.5  67   $\Gamma_{2}$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \gamma}}$ ($1.174$ $\pm0.035$ ) $\%$ S=1.5  67   $\Gamma_{3}$ ${{\mathit \gamma}}$ positronium ($1.82$ $\pm0.29$) $ \times 10^{-9}$ 67   $\Gamma_{4}$ ${{\mathit e}^{+}}{{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit e}^{-}}$ ($3.34$ $\pm0.16$) $ \times 10^{-5}$ 67   $\Gamma_{5}$ ${{\mathit e}^{+}}{{\mathit e}^{-}}$ ($6.46$ $\pm0.33$) $ \times 10^{-8}$ 67   $\Gamma_{6}$ 4 ${{\mathit \gamma}}$ $<2$ $\times 10^{-8}$ CL=90% 67   $\Gamma_{7}$ invisible $<4.4$ $\times 10^{-9}$ CL=90%     $\Gamma_{8}$ ${{\mathit \nu}_{{{e}}}}{{\overline{\mathit \nu}}_{{{e}}}}$ $<1.7$ $\times 10^{-6}$ CL=90% 67   $\Gamma_{9}$ ${{\mathit \nu}_{{{\mu}}}}{{\overline{\mathit \nu}}_{{{\mu}}}}$ $<1.6$ $\times 10^{-6}$ CL=90% 67   $\Gamma_{10}$ ${{\mathit \nu}_{{{\tau}}}}{{\overline{\mathit \nu}}_{{{\tau}}}}$ $<2.1$ $\times 10^{-6}$ CL=90% 67   $\Gamma_{11}$ ${{\mathit \gamma}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$ $<1.9$ $\times 10^{-7}$ CL=90% 67   ▸  exp Charge conjugation ($\mathit C$) or Lepton Family number ($\mathit LF$) violating modes $\Gamma_{12}$ 3 ${{\mathit \gamma}}$ C $<3.1$ $\times 10^{-8}$ CL=90% 67   $\Gamma_{13}$ ${{\mathit \mu}^{+}}{{\mathit e}^{-}}$ LF $<3.8$ $\times 10^{-10}$ CL=90% 26   $\Gamma_{14}$ ${{\mathit \mu}^{-}}{{\mathit e}^{+}}$ LF $<3.2$ $\times 10^{-10}$ CL=90% 26   $\Gamma_{15}$ ${{\mathit \mu}^{+}}{{\mathit e}^{-}}{+}$ ${{\mathit \mu}^{-}}{{\mathit e}^{+}}$ LF $<3.6$ $\times 10^{-10}$ CL=90% 26

[1] The ${{\mathit \pi}^{\pm}}$ mass has increased by three (old) standard deviations since our 1992 edition, and the ${{\mathit \pi}^{0}}$ mass, which is determined using the mass difference (${\mathit m}_{{{\mathit \pi}^{\pm}}}–{\mathit m}_{{{\mathit \pi}^{0}}}$), has increased accordingly. See the ``Note on the Charged Pion Mass'' in these Particle Listings for a discussion.

Constrained Fit information