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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: S014

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

We have omitted some results that have been superseded by later experiments. The omitted results may be found in our 1988 edition Physics Letters $\mathbf {B204}$ (1988).

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${{\mathit \eta}}$ MASS $547.862$ $\pm0.017$ MeV

${{\mathit \eta}}$ WIDTH $1.31$ $\pm0.05$ keV

▸  exp ${{\mathit \eta}}$ $\mathit C$-NONCONSERVING DECAY PARAMETERS

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ LEFT-RIGHT ASYMMETRY PARAMETER $0.0009^{+0.0011}_{-0.0012}$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ SEXTANT ASYMMETRY PARAMETER $0.0012^{+0.0010}_{-0.0011}$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ QUADRANT ASYMMETRY PARAMETER ($-9$ $\pm9$) $ \times 10^{-4}$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ LEFT-RIGHT ASYMMETRY PARAMETER $0.009$ $\pm0.004$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ PARAMETER $\beta $ (${\mathit D}{\mathrm -wave}$) $-0.02$ $\pm0.07$  (S = 1.3)

▸  exp ${{\mathit \eta}}$ $\mathit CP$-NONCONSERVING DECAY PARAMETER

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ DECAY-PLANE ASYMMETRY PARAMETER ${{\mathit A}_{{{\phi}}}}$ $-0.006$ $\pm0.031$

▸  exp ENERGY DEPENDENCE OF ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}}$ DALITZ PLOTS

PARAMETERS FOR ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$

$\alpha $ PARAMETER FOR ${{\mathit \eta}}$ $\rightarrow$ 3 ${{\mathit \pi}^{0}}$ $-0.0296$ $\pm0.0016$  (S = 1.7)

PARAMETER $\Lambda $ IN ${{\mathit \eta}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}{{\mathit \gamma}}$ DECAY $0.721$ $\pm0.011$ ${\mathrm {GeV/}}\mathit c{}^{2}$

${{\mathit \eta}}$ DECAY MODES

Mode   Fraction ($\Gamma_i$ / $\Gamma$) Scale Factor/ Conf. Level P(MeV/c)   ▸  exp Neutral modes $\Gamma_{1}$ neutral modes ($71.95$ $\pm0.29$ ) $\%$ S=1.3      $\Gamma_{2}$ 2 ${{\mathit \gamma}}$ ($39.36$ $\pm0.18$ ) $\%$ S=1.1  274   $\Gamma_{3}$ 3 ${{\mathit \pi}^{0}}$ ($32.56$ $\pm0.21$ ) $\%$ S=1.2  179   $\Gamma_{4}$ ${{\mathit \pi}^{0}}$2 ${{\mathit \gamma}}$ ($2.55$ $\pm0.22$) $ \times 10^{-4}$ 257   $\Gamma_{5}$ 2 ${{\mathit \pi}^{0}}$2 ${{\mathit \gamma}}$ $<1.2$ $\times 10^{-3}$ CL=90% 238   $\Gamma_{6}$ 4 ${{\mathit \gamma}}$ $<2.8$ $\times 10^{-4}$ CL=90% 274   $\Gamma_{7}$ invisible $<1.0$ $\times 10^{-4}$ CL=90%     ▸  exp Charged modes $\Gamma_{8}$ charged modes ($28.05$ $\pm0.29$ ) $\%$ S=1.3      $\Gamma_{9}$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$ ($23.02$ $\pm0.25$ ) $\%$ S=1.2  174   $\Gamma_{10}$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ ($4.28$ $\pm0.07$ ) $\%$ S=1.1  236   $\Gamma_{11}$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \gamma}}$ ($7.00$ $\pm0.22$) $ \times 10^{-3}$ S=1.1  274   $\Gamma_{12}$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \gamma}}$ ($3.1$ $\pm0.4$) $ \times 10^{-4}$ 253   $\Gamma_{13}$ ${{\mathit e}^{+}}{{\mathit e}^{-}}$ $<7$ $\times 10^{-7}$ CL=90% 274   $\Gamma_{14}$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ($5.8$ $\pm0.8$) $ \times 10^{-6}$ 253   $\Gamma_{15}$ 2 ${{\mathit e}^{+}}$2 ${{\mathit e}^{-}}$ ($2.40$ $\pm0.22$) $ \times 10^{-5}$ 274   $\Gamma_{16}$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ (${{\mathit \gamma}}$) ($2.68$ $\pm0.11$) $ \times 10^{-4}$ 235   $\Gamma_{17}$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ $<1.6$ $\times 10^{-4}$ CL=90% 253   $\Gamma_{18}$ 2 ${{\mathit \mu}^{+}}$2 ${{\mathit \mu}^{-}}$ ($5.0$ $\pm1.3$) $ \times 10^{-9}$ 161   $\Gamma_{19}$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $<3.6$ $\times 10^{-4}$ CL=90% 113   $\Gamma_{20}$ ${{\mathit \pi}^{+}}{{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}$ + c.c. $<1.7$ $\times 10^{-4}$ CL=90% 256   $\Gamma_{21}$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$2 ${{\mathit \gamma}}$ $<2.1$ $\times 10^{-3}$ 236   $\Gamma_{22}$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}{{\mathit \gamma}}$ $<6$ $\times 10^{-4}$ CL=90% 174   $\Gamma_{23}$ ${{\mathit \pi}^{0}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \gamma}}$ $<3$ $\times 10^{-6}$ CL=90% 210   ▸  exp Charge conjugation ($\mathit C$), Parity ($\mathit P$), Charge conjugation ${\times }$ Parity ($\mathit CP$), or Lepton Family number ($\mathit LF$) violating modes $\Gamma_{24}$ ${{\mathit \pi}^{0}}{{\mathit \gamma}}$ C [1] $<9$ $\times 10^{-5}$ CL=90% 257   $\Gamma_{25}$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ CP|P $<4.4$ $\times 10^{-6}$ CL=90% 236   $\Gamma_{26}$ 2 ${{\mathit \pi}^{0}}$ CP|P $<3.5$ $\times 10^{-4}$ CL=90% 238   $\Gamma_{27}$ 2 ${{\mathit \pi}^{0}}{{\mathit \gamma}}$ C $<5$ $\times 10^{-4}$ CL=90% 238   $\Gamma_{28}$ 3 ${{\mathit \pi}^{0}}{{\mathit \gamma}}$ C $<6$ $\times 10^{-5}$ CL=90% 179   $\Gamma_{29}$ 3 ${{\mathit \gamma}}$ C $<1.6$ $\times 10^{-5}$ CL=90% 274   $\Gamma_{30}$ 4 ${{\mathit \pi}^{0}}$ CP|P $<6.9$ $\times 10^{-7}$ CL=90% 40   $\Gamma_{31}$ ${{\mathit \pi}^{0}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ C [2] $<8$ $\times 10^{-6}$ CL=90% 257   $\Gamma_{32}$ ${{\mathit \pi}^{0}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ C [2] $<5$ $\times 10^{-6}$ CL=90% 210   $\Gamma_{33}$ ${{\mathit \mu}^{+}}{{\mathit e}^{-}}{+}$ ${{\mathit \mu}^{-}}{{\mathit e}^{+}}$ LF $<6$ $\times 10^{-6}$ CL=90% 264

[1] Forbidden by angular momentum conservation. [2] $\mathit C$ parity forbids this to occur as a single-photon process.

Constrained Fit information