Possible Existence of Light Hypernuclei

Abstract

The possible existence of light Σ hypernuclei is discussed together with their general binding mechanism. The coupling between the isotriplet Σ particle (Σ+, Σ0 and Σ−) and the corresponding nuclear core isomultiplet and supermultiplet which comes from the strong isospin dependent and isospin-spin dependent terms of Σ-N interaction plays a crucial role to produce bound states of light Σ hypernuclei. It is found that 1) an almost pure isospin 1/2 bound (ground) state appears in Σ4He mainly due to the cooperative contribution of the (tN·tΣ) and (tN·tΣ)(sN·sΣ) terms of Σ-N interaction, and 2) an isospin-breaking bound (ground) state appears in Σ7Li mainly due to the (tN·tΣ)(sN·sΣ) term of Σ-N interaction. We discuss in detail the different binding mechanism between Σ4He and Σ7Li and propose a threshold rule for the formation of bound Σ hypernuclear states. From the viewpoint of the threshold rule, the possible existence of other typical light Σ hypernuclei, Σ7H, Σ9Be and Σ11B, are investigated together with their binding mechanism on the same footing as Σ4He and Σ7Li.