pdgLive

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:

${{\mathit \eta}^{\,'}{(958)}}$

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

${{\mathit \eta}^{\,'}{(958)}}$ MASS

$957.78 \pm0.06$ MeV

${{\mathit \eta}^{\,'}{(958)}}$ WIDTH

$0.188 \pm0.006$ MeV

${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}}{{\mathit \pi}}$ DECAY PARAMETERS $\vert $MATRIX ELEMENT$\vert ^2$ = $\vert $1 + $\alpha {}\mathit Y\vert ^2$ + $\mathit C{}\mathit X$ + $\mathit D{}\mathit X{}^{2}$

$\mathit Re(\alpha $) decay parameter

$\mathit Im(\alpha $) decay parameter

$\mathit C$ decay parameter

$\mathit D$ decay parameter

${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}}{{\mathit \pi}}$ DECAY PARAMETERS $\vert $MATRIX ELEMENT$\vert ^2$ ${}\propto$ 1 + $\mathit a~Y$ + $\mathit b~Y{}^{2}$ + $\mathit c~X$ + $\mathit d~X{}^{2}$

$\mathit a$ decay parameter

$\mathit b$ decay parameter

$\mathit c$ decay parameter

$\mathit d$ decay parameter

${{\mathit \eta}^{\,'}{(958)}}$ $\beta $ PARAMETER $\vert $MATRIX ELEMENT$\vert ^2$ = (1 + 2$\beta {{\mathit Z}}$)

$\beta $ decay parameter

$-0.61 \pm0.08$ (S = 1.2)

${{\mathit \eta}^{\,'}{(958)}}{}^{C}$-NONCONSERVING DECAY PARAMETER

DECAY ASYMMETRY PARAMETER FOR ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$

$-0.03 \pm0.04$

${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ TRANSITION FORM FACTOR SLOPE

$1.62 \pm0.17$ GeV${}^{-2}$

${{\mathit \eta}^{\,'}{(958)}}$ DECAY MODES ▸ Expand all decays

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \eta}}$

$(42.5\pm{0.5})\%$

${{\mathit \rho}^{0}}{{\mathit \gamma}}$ (including non-resonant ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$)

$(29.5\pm{0.4})\%$

${{\mathit \rho}^{0}}{{\mathit \gamma}}$

${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit \eta}}$

$(22.4\pm{0.5})\%$

${{\mathit \omega}}{{\mathit \gamma}}$

$(2.52\pm{0.07})\%$

${{\mathit \omega}}{{\mathit e}^{+}}{{\mathit e}^{-}}$

$(2.0\pm{0.4})\times 10^{-4}$

${{\mathit \gamma}}{{\mathit \gamma}}$

$(2.307\pm{0.033})\%$

3 ${{\mathit \pi}^{0}}$

$(2.50\pm{0.17})\times 10^{-3}$

${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \gamma}}$

$(1.13\pm{0.28})\times 10^{-4}$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$

$(2.0\pm{0.4})\times 10^{-5}$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$

$(3.61\pm{0.17})\times 10^{-3}$

( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{0}}$) S-wave

$(3.8\pm{0.5})\times 10^{-3}$

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

$(7.4\pm{2.3})\times 10^{-4}$

2( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$)

$(8.4\pm{0.9})\times 10^{-5}$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$2 ${{\mathit \pi}^{0}}$

$(1.8\pm{0.4})\times 10^{-4}$

2( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$) neutrals

2( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$) ${{\mathit \pi}^{0}}$

$<1.8\times 10^{-3}$

2( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$) 2 ${{\mathit \pi}^{0}}$

3( ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$)

$<3.1\times 10^{-5}$

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

$<4\times 10^{-5}$

${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$

$(2.42\pm{0.10})\times 10^{-3}$

${{\mathit \pi}^{+}}{{\mathit e}^{-}}{{\mathit \nu}_{{e}}}$ + c.c.

$<2.1\times 10^{-4}$

${{\mathit \gamma}}{{\mathit e}^{+}}{{\mathit e}^{-}}$

$(4.91\pm{0.27})\times 10^{-4}$

${{\mathit \pi}^{0}}{{\mathit \gamma}}{{\mathit \gamma}}$

$(3.20\pm{0.24})\times 10^{-3}$

${{\mathit \pi}^{0}}{{\mathit \gamma}}{{\mathit \gamma}}$ (non resonant)

$(6.2\pm{0.9})\times 10^{-4}$

${{\mathit \eta}}{{\mathit \gamma}}{{\mathit \gamma}}$

$<1.33\times 10^{-4}$

4 ${{\mathit \pi}^{0}}$

$<4.94\times 10^{-5}$

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

$<5.6\times 10^{-9}$

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

$(4.5\pm{1.1})\times 10^{-6}$

$<6\times 10^{-4}$

▸	Charge conjugation ($\mathit C$), Parity ($\mathit P$), Lepton family number ($\mathit LF$) violating modes

FOOTNOTES

Constrained Fit information

Except where otherwise noted, content of the 2023 Review of Particle Physics is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy), JPS and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2023. See LBNL disclaimers.