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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:

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

$I^G(J^{P})$ = $1^-(0^{-})$

We have omitted some results that have been superseded by later experiments.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 $\mathit a$

$\mathit R$, 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.

${{\mathit \mu}^{+}}{{\mathit \nu}_{{{\mu}}}}$

$(99.98770\pm{0.00004})\%$

${{\mathit \mu}^{+}}{{\mathit \nu}_{{{\mu}}}}{{\mathit \gamma}}$

$(2.00\pm{0.25})\times 10^{-4}$

${{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}$

$(1.230\pm{0.004})\times 10^{-4}$

${{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}{{\mathit \gamma}}$

$(7.39\pm{0.05})\times 10^{-7}$

${{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}{{\mathit \pi}^{0}}$

$(1.036\pm{0.006})\times 10^{-8}$

${{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$

$(3.2\pm{0.5})\times 10^{-9}$

${{\mathit \mu}^{+}}{{\mathit \nu}_{{{\mu}}}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$

$<9\times 10^{-6}$

${{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}{{\mathit \nu}}{{\overline{\mathit \nu}}}$

$<1.6\times 10^{-7}$

▸	Lepton Family number ($\mathit LF$) or Lepton number ($\mathit L$) violating modes

FOOTNOTES

Except where otherwise noted, content of the 2024 Review of Particle Physics is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy) and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2024. See LBNL disclaimers.