≡ Hypernuclei

We consider the possibility of forming doubly strange Ξ hypernuclei via the (K^-, K) reactions on various nuclear targets. Because of the high momentum transfer involved, even at 0°, the formation of high spin states is strongly favored. The available experimental information on the elementary processes K^-p → K⁺Ξ^- or K⁰Ξ⁰ is reviewed, leading to the determination of an optimum incident K^- momentum of about 1.9 GeV/c for the forward formation of discrete Ξ hypernuclear states. The cross section for the process ΞN → ΛΛ, responsible for the damping width of Ξ states in nuclei, is estimated theoretically and the very limited experimental data are also reviewed. The resulting Ξ hypernuclear widths are of order 5 MeV. Emulsion data which have been interpreted as due to the existence of ΛΛ and Ξ^- hypernuclei are discussed and used to obtain an approximate Ξ nuclear well-depth of 21-24 MeV. For this range of values, spectra of single particle Ξ^- states are obtained, and calculated angular distributions for the formation of simple Ξ^- particle-proton hole states in ⁴He, ¹²C and ²⁸Si targets are presented. The peak 0° lab cross section at p_lab = 1.9 GeV/c for such states ranges from tens of nb sr to about 1 μb sr. We briefly mention other methods for forming Ξ hypernuclei, such as the three body reaction K^-N → KπΞ (or K^-p → K⁺K⁰Ω^- for Ω^- hypernuclei).