Constraining CP violation in the main decay of the neutral Sigma hyperon

The Σ 0 and Λ hyperons are close relatives of the neutron, being related by flavour SU(3) symmetry. This allows to estimate an upper limit for the electric dipole transition moment (EDTM) of the Σ 0 -Λ transition, based on the experimental knowledge of the upper limit of the neutron electric dipole moment. The three-body decay Σ 0 → γ p π − could show an angular asymmetry due to the interference of parity violating and conserving amplitudes in both the first and second step of the decay chain Σ 0 → Λ γ → γ p π − . This angular asymmetry, which will be measured at e.g. PANDA for both particle and antiparticle decays, is determined in this work from the Σ 0 -Λ EDTM, where a CP violating QCD theta-vacuum-angle term has been included. It turns out to be below any experimental resolution that one can expect in the foreseeable future. Any experimental significance would therefore point to physics beyond the Standard Model.