hypernucleus

A hypernucleus is a bound state in which one or more nucleons in a ordinary atomic nucleus are replaced by one or more hyperons, baryons that contain strange quarks. The most common hyperon in hypernuclei is the Lambda (Λ). The addition of a hyperon introduces strangeness into the nucleus while the overall charge is determined by the remaining protons and neutrons. Single-hypernuclei contain one Λ; double-hypernuclei contain two hyperons, typically ΛΛ.

Hypernuclei are produced in high-energy reactions, such as kaon capture on nuclear targets, meson-induced reactions, or relativistic heavy-ion collisions. They are studied through spectroscopy, decay products, and gamma-ray signatures that reveal their energy levels and binding energies. The bound hyperon decays weakly, so a hypernucleus can be identified by characteristic weak-decay modes and by its relatively long lifetime compared with typical strong-interaction processes. Nonmesonic decays, such as ΛN → NN, also contribute to the decay channels inside the nucleus.

Studying hypernuclei provides information about hyperon–nucleon and hyperon–hyperon interactions, which are not accessible in ordinary nuclei. This helps refine models of the strong force in systems with strangeness and informs the behavior of dense nuclear matter, including conditions relevant to neutron stars where hyperons may appear.

Historical milestones include the initial observation of Λ-hypernuclei in the 1950s, and notable measurements such as the Nagara event in 2001, which offered precise data on the ΛΛ interaction in double-hypernuclei. Examples of hypernuclei include light to medium-mass Λ-hypernuclei such as 12ΛC.