Estimates of the isospin-violating Λb→Σ0

We analyse the two purely isospin-violating decays $\Lambda_b\rightarrow \Sigma^0 \phi$ and $\Lambda_b\rightarrow \Sigma^0 J/\psi$, proceed merely via the exchange topologies, in the framework of perturbative QCD approach. Assuming $\Sigma^0$ baryon belongs to the idealized isospin triplet with quark components of $usd$, the branching ratios of the two decay modes are predicted to be tiny, of the order $10^{-8}-10^{-9}$, leading to a difficulty in observing them. We then extend our study to include the $\Sigma-\Lambda$ mixing.It is found that the mixing has significant effect on the $\Lambda_b\rightarrow \Sigma$ decays, especially it can greatly increase the rate of the $J/\psi$ process, by as much as two orders of magnitude, yield $10^{-7}$, which should be searchable in the future. We also estimate a set of asymmetry observables with and without the mixing effect, which will be tested in coming experiments.