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

Abstract

On general grounds based on quantum field theory the decay amplitude for Σ 0 → Λγ consists of a parity conserving magnetic and a parity violating electric dipole transition moment. Because of the subsequent self-analyzing weak decay of the Λ hyperon the interference between magnetic and electric dipole transition moment leads to an asymmetry in the angular distribution. Comparing the decay distributions for the Σ 0 hyperon and its antiparticle gives access to possible C and CP violation. Based on flavor SU(3) symmetry the present upper limit on the neutron electric dipole moment can be translated to an upper limit for the angular asymmetry. It turns out to be far below any experimental resolution that one can expect in the foreseeable future. Thus any true observation of a CP violating angular asymmetry would constitute physics beyond the standard model, even if extended by a CP violating QCD theta-vacuum-angle term.

Electromagnetic transition form factors and Dalitz decays of hyperons

“…The second concrete example for which we will provide quantitative results is the Λ(1520). It is the strange baryon next in mass after covering Σ and Σ(1385) previously [1,4,5,27,28] and the Λ(1405) in the present work. Above the Λ(1520) our low-energy techniques might fail to work.…”

“…Examples for the latter are the states Σ(1385) and Σ 0 , respectively. Transitions of those states have been studied by the group of one of the authors in [1,4,5,27,28].…”

Polarised and entangled hyperon-antihyperon pairs in BESIII

“…[17,29]. Furthermore, electromagnetic decays of polarised Σ 0 hyperons provide a test for strong CP violation [30]. The formalism for + − → Σ 0Σ0 is derived in Ref.…”

Hyperons - a strange key to the strong interaction

“…[57]. The latter is an electromagnetic decay and is therefore very unlikely to violate CP symmetry [58]. However, this means that even small signals would indicate new physics.…”