Double-Λ and Ξ hypernuclei : Findings and Prospects
Kazuma Nakazawa 1, 2
1 High Energy Nuclear Physics Laboratory, RIKEN
2 Faculty of education, Gifu University, Japan
Since the discovery of the doubly-strange hypernucleus in 1963, many efforts have been made but no new discoveries have been made. In the 1980s, we introduced the Emulsion-Counter "Hybrid-method" combining real-time detectors and nuclear emulsion, which led to the discovery of the charn and beauty particles, to our experiment to search for doubly-strange hypernucleus. As a result, we confirmed the existence of double-Λ hypernucleus, which decayed sequentially, at an absorption point of a Ξ- particle in the KEK-E176 experiment. With developed hybrid method, the E373 (KEK) experiment succeeded in the unique identification of 6ΛΛHe, where the interaction between Λ and Λ particles was understood to be weakly attractive. In the further improved E07 (J-PARC) experiment, we succeeded in detecting 33 cases of doubly-strange hypernuclei and the ground state of Ξ hypernuclei. From the 47 cases we have detected so far and one case in 1963, we found that the interaction between two Λ particles is a weak attraction and that the energy at which two Λ particles bind to a nucleus seems to depend linearly on the nuclear mass number. Additionally, the existence of the Ξ hypernucleus was confirmed, then the interaction between the Ξ and nucleon works attractively. Regarding the 15ΞC hypernuclei, the level stracture can be seen. We are currently developing an efficient detection method for the production and decay of doubly-strange hypernuclei by probing the entire volume of the emulsion and applying a machine learning model, without relying on information from real-time detectors. This development is expected to detect a large number of double-Λ hypernuclei emitted from the K- reaction point as well as the Ξ- absorption, which shall conduce to very important and more reliable information for understanding baryons in a unified manner under SU(3)f symmetry.