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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 PDGID: S019

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

We have omitted some results that have been superseded by later experiments.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

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${{\mathit \Sigma}^{+}}$ MASS $1189.37$ $\pm0.06$ MeV (S = 1.8)

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

(${\mathit \mu}_{{{\mathit \Sigma}^{+}}}$ $+$ ${\mathit \mu}_{{{\overline{\mathit \Sigma}}^{-}}}$) $/$ ${\mathit \mu}_{{{\mathit \Sigma}^{+}}}$ $0.014$ $\pm0.015$

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

$\alpha _{0}$ FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{0}}$ $-0.982$ $\pm0.014$

${{\overline{\mathit \alpha}}_{{{0}}}}$ FOR ${{\overline{\mathit \Sigma}}^{-}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \pi}^{0}}$ $0.99$ $\pm0.04$

(${{\mathit \alpha}_{{{0}}}}$ + ${{\overline{\mathit \alpha}}_{{{0}}}}$) / (${{\mathit \alpha}_{{{0}}}}$ $−$ ${{\overline{\mathit \alpha}}_{{{0}}}}$) $0.00$ $\pm0.04$

$\phi _{0}$ ANGLE FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{0}}$ ($\phi _{0}$ = $\beta /\gamma $) $36$ $\pm34$ $^\circ{}$

$\alpha _{+}$ / $\alpha _{0}$ $-0.0498$ $\pm0.0027$

$\alpha _{+}$ FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \pi}^{+}}$ $0.0489$ $\pm0.0026$

$\phi _{+}$ ANGLE FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \pi}^{+}}$ ($\phi _{+}$ = $\beta /\gamma $) $167$ $\pm20$ $^\circ{}$ (S = 1.1)

${{\overline{\mathit \alpha}}_{{{-}}}}$ FOR ${{\overline{\mathit \Sigma}}^{-}}$ $\rightarrow$ ${{\overline{\mathit n}}}{{\mathit \pi}^{-}}$ $-0.057$ $\pm0.005$

${{\overline{\mathit \alpha}}_{{{-}}}}$ / ${{\overline{\mathit \alpha}}_{{{0}}}}$ $-0.057$ $\pm0.006$

(${{\mathit \alpha}_{{{+}}}}$ + ${{\overline{\mathit \alpha}}_{{{-}}}}$) / (${{\mathit \alpha}_{{{+}}}}$ $−$ ${{\overline{\mathit \alpha}}_{{{-}}}}$) $-0.08$ $\pm0.06$

$\alpha _{\gamma }$ FOR ${{\mathit \Sigma}^{+}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \gamma}}$ $-0.69$ $\pm0.05$

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

Mode   Fraction ($\Gamma_i$ / $\Gamma$) Scale Factor/ Conf. Level P(MeV/c)   $\Gamma_{1}$ ${{\mathit p}}{{\mathit \pi}^{0}}$ ($51.47$ $\pm0.30$ ) $\%$ 189   $\Gamma_{2}$ ${{\mathit n}}{{\mathit \pi}^{+}}$ ($48.43$ $\pm0.30$ ) $\%$ 185   $\Gamma_{3}$ ${{\mathit p}}{{\mathit \gamma}}$ ($1.04$ $\pm0.06$) $ \times 10^{-3}$ S=2.4  225   $\Gamma_{4}$ ${{\mathit n}}{{\mathit \pi}^{+}}{{\mathit \gamma}}$ [1] ($4.5$ $\pm0.5$) $ \times 10^{-4}$ 185   $\Gamma_{5}$ ${{\mathit \Lambda}}{{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}$ ($2.3$ $\pm0.4$) $ \times 10^{-5}$ 71   ▸  exp $\Delta \mathit S$ = $\Delta \mathit Q$ ($\mathit SQ$) violating modes or $\Delta \mathit S$ = 1 weak neutral current ($\mathit S1$) modes $\Gamma_{6}$ ${{\mathit n}}{{\mathit e}^{+}}{{\mathit \nu}_{{{e}}}}$ SQ $<5$ $\times 10^{-6}$ CL=90% 224   $\Gamma_{7}$ ${{\mathit n}}{{\mathit \mu}^{+}}{{\mathit \nu}_{{{\mu}}}}$ SQ $<3.0$ $\times 10^{-5}$ CL=90% 202   $\Gamma_{8}$ ${{\mathit p}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ S1 $<7$ $\times 10^{-6}$ 225   $\Gamma_{9}$ ${{\mathit p}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ S1 ($2.4^{+1.7}_{-1.3}$) $ \times 10^{-8}$ 121   $\Gamma_{10}$ ${{\mathit p}}{{\mathit \gamma}_{{{dark}}}}$ $<3.2$ $\times 10^{-5}$ CL=90%

[1] See the Listings below for the pion momentum range used in this measurement.

Constrained Fit information