Editing Hypernucleus (section)

=== Σ hypernuclei ===
The existence of hypernuclei containing a Σ baryon is less clear. Several experiments in the early 1980s reported bound hypernuclear states above the Λ [[separation energy]] and presumed to contain one of the slightly heavier Σ baryons, but experiments later in the decade ruled out the existence of such states.<ref name="Feliciello"/> Results from [[exotic atoms]] containing a Σ<sup>−</sup> bound to a nucleus by the [[electromagnetic force]] have found a net repulsive Σ–nucleon interaction in medium-sized and large hypernuclei, which means that no Σ hypernuclei exist in such mass range.<ref name="Feliciello"/> However, an experiment in 1998 definitively observed the light Σ hypernucleus {{PhysicsParticle|[[Helium|He]]|TL=4|BL=Σ}}.<ref name="Feliciello"/>