Why do we never observe the decay of this particle?

[oosgood]

Hey why do we observe the Ʃ(minus) decay into n+e+anti-e-neutrino?But never

Ʃ+--->n + positron+ ve( electron neutrino)

 

[ofirg]

First (although the notation is confusing) $Ʃ^{+}$ and $Ʃ^{-}$ are not a particle-antiparticle pair, they are patners in an isospin triplet. So there is no reason that the two decays should be related. $Ʃ^{+}$ is composed of suu and it would two W exchanges (netral vector bosons don't mix flavour), while $Ʃ^{-}$ is composed of sdd which requires only one W exchange.