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

INSPIRE   JSON PDGID: S018

${{\mathit \Lambda}}$ $I(J^P)$ = $0(1/2^{+})$

We have omitted some results that have been superseded by later experiments.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

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${{\mathit \Lambda}}$ MASS $1115.683$ $\pm0.006$ MeV

(${\mathit m}_{{{\mathit \Lambda}}}-{\mathit m}_{{{\overline{\mathit \Lambda}}}}$) $/$ ${\mathit m}_{{{\mathit \Lambda}}}$ ($-0.1$ $\pm1.1$) $ \times 10^{-5}$  (S = 1.6)

${{\mathit \Lambda}}$ MEAN LIFE ($2.617$ $\pm0.010$) $ \times 10^{-10}$ s (S = 1.5)

(${\mathit \tau}_{{{\mathit \Lambda}}}-{\mathit \tau}_{{{\overline{\mathit \Lambda}}}}$) / ${\mathit \tau}_{{{\mathit \Lambda}}}$ $0.0009$ $\pm0.0032$

${{\mathit \Lambda}}$ MAGNETIC MOMENT $-0.613$ $\pm0.004$ $\mu _{\mathit N}$

${{\mathit \Lambda}}$ ELECTRIC DIPOLE MOMENT $<1.5$ $\times 10^{-16}$ $\mathit e~$cm  CL=95%

▸  exp ${{\mathit \Lambda}}$ $\mathit CP$-violating decay-rate asymmetries

$\mathit A_{CP}({{\mathit p}}{{\mathit \mu}^{-}}{{\overline{\mathit \nu}}_{{{\mu}}}}$) in ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \mu}^{-}}{{\overline{\mathit \nu}}_{{{\mu}}}}$, ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \mu}^{+}}{{\mathit \nu}_{{{\mu}}}}$ $0.02$ $\pm0.14$

Limit on ${{\overline{\mathit \Lambda}}}{{\mathit \Lambda}}$ oscillations $<3.8$ $\times 10^{-18}$ GeV  CL=90%

▸  exp ${{\mathit \Lambda}}$ DECAY PARAMETERS

$\alpha _{−}$ FOR ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{-}}$ $0.746$ $\pm0.008$  (S = 2.4)

$\alpha _{+}$ FOR ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \pi}^{+}}$ $-0.758$ $\pm0.005$  (S = 1.2)

${{\overline{\mathit \alpha}}_{{{0}}}}$ FOR ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit n}}}{{\mathit \pi}^{0}}$ $-0.675$ $\pm0.011$  (S = 1.2)

${{\mathit \alpha}_{{{0}}}}$ FOR ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \pi}^{0}}$ $0.670$ $\pm0.012$

$\alpha _{{{\mathit \gamma}}}$ FOR ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \gamma}}$ $-0.16$ $\pm0.11$

$\phi $ ANGLE FOR ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{-}}$ (tan$\phi $ = $\beta $ / $\gamma $) $-6.5$ $\pm3.5$ $^\circ{}$

$\alpha _{0}$ / $\alpha _{−}$ = $\alpha\mathrm {({{\mathit \Lambda}} \rightarrow {{\mathit n}} {{\mathit \pi}^{0}})}$ / $\alpha\mathrm {({{\mathit \Lambda}} \rightarrow {{\mathit p}} {{\mathit \pi}^{-}})}$ $0.888^{+0.034}_{-0.030}$  (S = 1.7)

${{\overline{\mathit \alpha}}_{{{0}}}}$ / ${{\mathit \alpha}_{{{+}}}}$ in ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit n}}}{{\mathit \pi}^{0}}$, ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \pi}^{+}}$ $0.876^{+0.022}_{-0.020}$  (S = 1.4)

(${{\mathit \alpha}_{{{-}}}}$ + ${{\mathit \alpha}_{{{+}}}})/({{\mathit \alpha}_{{{-}}}}−{{\mathit \alpha}_{{{+}}}}$) in ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{-}}$, ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \pi}^{+}}$ $-0.003$ $\pm0.004$

(${{\mathit \alpha}_{{{0}}}}$ + ${{\overline{\mathit \alpha}}_{{{0}}}})/({{\mathit \alpha}_{{{0}}}}−{{\overline{\mathit \alpha}}_{{{0}}}}$) in ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit n}}{{\mathit \pi}^{0}}$, ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit n}}}{{\mathit \pi}^{0}}$ $0.001^{+0.010}_{-0.011}$

R = $\vert G_{E}/G_{M}\vert $ in ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{-}}$, ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \pi}^{+}}$ $0.96$ $\pm0.14$

$\Delta \Phi $ = $\Phi _{E}$ $−$ $\Phi _{M}$ in ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit p}}{{\mathit \pi}^{-}}$, ${{\overline{\mathit \Lambda}}}$ $\rightarrow$ ${{\overline{\mathit p}}}{{\mathit \pi}^{+}}$ $37$ $\pm13$ degrees

${\mathit g}_{{{\mathit A}}}$ / ${\mathit g}_{{{\mathit V}}}$ FOR ${{\mathit \Lambda}}$ $\rightarrow$ ${{\mathit p}}{{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}$ [1] $-0.718$ $\pm0.015$

${{\mathit \Lambda}}$ DECAY MODES

Mode   Fraction ($\Gamma_i$ / $\Gamma$) Scale Factor/ Conf. Level P(MeV/c)   $\Gamma_{1}$ ${{\mathit p}}{{\mathit \pi}^{-}}$ ($64.1$ $\pm0.5$ ) $\%$ 101   $\Gamma_{2}$ ${{\mathit n}}{{\mathit \pi}^{0}}$ ($35.9$ $\pm0.5$ ) $\%$ 104   $\Gamma_{3}$ ${{\mathit n}}{{\mathit \gamma}}$ ($8.3$ $\pm0.7$) $ \times 10^{-4}$ 162   $\Gamma_{4}$ ${{\mathit p}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ [2] ($8.5$ $\pm1.4$) $ \times 10^{-4}$ 101   $\Gamma_{5}$ ${{\mathit p}}{{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}$ ($8.34$ $\pm0.14$) $ \times 10^{-4}$ 163   $\Gamma_{6}$ ${{\mathit p}}{{\mathit \mu}^{-}}{{\overline{\mathit \nu}}_{{{\mu}}}}$ ($1.51$ $\pm0.19$) $ \times 10^{-4}$ 131   ▸  exp Lepton ($\mathit L$) and/or Baryon ($\mathit B$) number violating decay modes $\Gamma_{7}$ ${{\mathit \pi}^{+}}{{\mathit e}^{-}}$ B|L $<6$ $\times 10^{-7}$ CL=90% 549   $\Gamma_{8}$ ${{\mathit \pi}^{+}}{{\mathit \mu}^{-}}$ B|L $<6$ $\times 10^{-7}$ CL=90% 544   $\Gamma_{9}$ ${{\mathit \pi}^{-}}{{\mathit e}^{+}}$ B|L $<4$ $\times 10^{-7}$ CL=90% 549   $\Gamma_{10}$ ${{\mathit \pi}^{-}}{{\mathit \mu}^{+}}$ B|L $<6$ $\times 10^{-7}$ CL=90% 544   $\Gamma_{11}$ ${{\mathit K}^{+}}{{\mathit e}^{-}}$ B|L $<2$ $\times 10^{-6}$ CL=90% 449   $\Gamma_{12}$ ${{\mathit K}^{+}}{{\mathit \mu}^{-}}$ B|L $<3$ $\times 10^{-6}$ CL=90% 441   $\Gamma_{13}$ ${{\mathit K}^{-}}{{\mathit e}^{+}}$ B|L $<2$ $\times 10^{-6}$ CL=90% 449   $\Gamma_{14}$ ${{\mathit K}^{-}}{{\mathit \mu}^{+}}$ B|L $<3$ $\times 10^{-6}$ CL=90% 441   $\Gamma_{15}$ ${{\mathit K}_S^0}$ ${{\mathit \nu}}$ B|L $<2$ $\times 10^{-5}$ CL=90% 447   $\Gamma_{16}$ ${{\overline{\mathit p}}}{{\mathit \pi}^{+}}$ B $<9$ $\times 10^{-7}$ CL=90% 101   $\Gamma_{17}$ invisible $<7.4$ $\times 10^{-5}$ CL=90%

[1] The parameters ${\mathit g}_{{{\mathit A}}}$, ${\mathit g}_{{{\mathit V}}}$, and ${\mathit g}_{\mathit WM}$ for semileptonic modes are defined by ${{\overline{\mathit B}}_{{{f}}}}[{{\mathit \gamma}_{{{\lambda}}}}({\mathit g}_{{{\mathit V}}}$ $+$ ${\mathit g}_{{{\mathit A}}}{{\mathit \gamma}_{{{5}}}}$) $+$ $\mathit i({\mathit g}_{\mathit WM}/{\mathit m}_{{{\mathit B}_{{{i}}}}}$) $\sigma _{\lambda \nu }$ $\mathit q{}^{\nu }]\mathit B_{\mathit i}$, and $\phi _{\mathit AV}$ is defined by ${\mathit g}_{{{\mathit A}}}/{\mathit g}_{{{\mathit V}}}$ = $\vert {\mathit g}_{{{\mathit A}}}/{\mathit g}_{{{\mathit V}}}\vert \mathit e{}^{\mathit i\phi _{\mathit AV}}$. See the ``Note on Baryon Decay Parameters'' in the neutron Particle Listings. [2] See the Listings below for the pion momentum range used in this measurement.

Constrained Fit information