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${{\mathit \Sigma}}$ BARYONS
($\mathit S$ = $-1$, $\mathit I$ = 1)
${{\mathit \Sigma}^{+}}$ = ${\mathit {\mathit u}}$ ${\mathit {\mathit u}}$ ${\mathit {\mathit s}}$, ${{\mathit \Sigma}^{0}}$ = ${\mathit {\mathit u}}$ ${\mathit {\mathit d}}$ ${\mathit {\mathit s}}$, ${{\mathit \Sigma}^{-}}$ = ${\mathit {\mathit d}}$ ${\mathit {\mathit d}}$ ${\mathit {\mathit s}}$

INSPIRE JSON (beta) PDGID:

${{\mathit \Sigma}^{+}}$

$I(J^P)$ = $1(1/2^{+})$

We have omitted some results that have been superseded by later experiments. See our earlier editions.

${{\mathit \Sigma}^{+}}$ MASS

$1189.37 \pm0.07$ MeV (S = 2.2)

${{\mathit \Sigma}^{+}}$ MEAN LIFE

$(8.018 \pm0.026) \times 10^{-11}$ s

(${\mathit \tau}_{{{\mathit \Sigma}^{+}}}–{\mathit \tau}_{{{\overline{\mathit \Sigma}}^{-}}}$) $/$ ${\mathit \tau}_{{{\mathit \Sigma}^{+}}}$

$-0.0006 \pm0.0012$

${{\mathit \Sigma}^{+}}$ MAGNETIC MOMENT

$2.458 \pm0.010$ $\mu _{\mathit N}$ (S = 2.1)

(${\mathit \mu}_{{{\mathit \Sigma}^{+}}}$ $+$ ${\mathit \mu}_{{{\overline{\mathit \Sigma}}^{-}}}$) $/$ ${\mathit \mu}_{{{\mathit \Sigma}^{+}}}$

$0.014 \pm0.015$

${{\mathit \Sigma}^{+}}$ DECAY PARAMETERS

$\alpha _{0}$ FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{0}}$

$-0.982 \pm0.014$

${{\overline{\mathit \alpha}}_{{0}}}$ FOR ${{\overline{\mathit \Sigma}}^{-}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \pi}^{0}}$

(${{\mathit \alpha}_{{0}}}$ + ${{\overline{\mathit \alpha}}_{{0}}}$) $/$ (${{\mathit \alpha}_{{0}}}$ $−$ ${{\overline{\mathit \alpha}}_{{0}}}$)

$\phi _{0}$ ANGLE FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{0}}$ ($\phi _{0}$ = $\beta /\gamma $)

$36 \pm34$ $^\circ{}$

$\alpha _{+}$ $/$ $\alpha _{0}$

$-0.069 \pm0.013$

$\alpha _{+}$ FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \pi}^{+}}$

$0.068 \pm0.013$

$\phi _{+}$ ANGLE FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \pi}^{+}}$ ($\phi _{+}$ = $\beta /\gamma $)

$167 \pm20$ $^\circ{}$ (S = 1.1)

$\alpha _{\gamma }$ FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \gamma}}$

$-0.76 \pm0.08$

${{\mathit \Sigma}^{+}}$ DECAY MODES ▸ Expand all decays

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

$(51.57\pm{0.30})\%$

${{\mathit n}}{{\mathit \pi}^{+}}$

$(48.31\pm{0.30})\%$

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

$(1.23\pm{0.05})\times 10^{-3}$

${{\mathit n}}{{\mathit \pi}^{+}}{{\mathit \gamma}}$

$(4.5\pm{0.5})\times 10^{-4}$

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

$(2.0\pm{0.5})\times 10^{-5}$

▸	$\Delta \mathit S$ = $\Delta \mathit Q$ ($\mathit SQ$) violating modes or $\Delta \mathit S$ = 1 weak neutral current ($\mathit S1$) 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.