Study of light hypernuclei in Europe: The hypertriton and nnΛ puzzles

¹ Instituto de Estructura de la Materia - CSIC, Madrid, Spain
² Institute for Nuclear Physics, Johannes Gutenberg University, Mainz, Germany,
³ Helmholtz Institute Mainz, Johannes Gutenberg University, Mainz, Germany,
⁴ GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany,
⁵ Institut für Kernphysik, Universität Köln, Koln, Germany,
⁶ IGFAE, Universidade de Santiago de Compostela, Santiago de Compostela, Spain,
⁷ Jozef Stefan Institute, Ljubljana, Slovenia,
⁸ University of Ljubljana, Ljubljana, Slovenia,
⁹ Justus-Liebig Universität Giessen, Giessen, Germany,
¹⁰ University of Groningen, Groningen, The Netherlands,
¹¹ High Energy Nuclear Physics Laboratory, RIKEN Cluster for Pioneering Research, RIKEN, Wako, Japan,
¹² Tokyo Institute of Technology, Tokyo, Japan,
¹³ Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China,
¹⁴ School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing, China,
¹⁵ Institut fur Kernphysik, Forschungszentrum Julich, Julich, Germany,
¹⁶ Institut fur Kernphysik, Technische Universitat Darmstadt, Darmstadt, Germany,
¹⁷ Meson Science Laboratory, Cluster for Pioneering Research, RIKEN, Wako, Japan,
¹⁸ Nishina Center for Accelerator-Based Science, RIKEN, Wako, Japan,
¹⁹ Graduate School of Engineering, Gifu University, Gifu, Japan
²⁰ INFN, Laboratori Nazionali di Frascati, Frascati, Roma, Italy,
²¹ Institute of Physics, Jagiellonian University, Krakow, Poland,
²² TH Mittelhessen University of Applied Sciences, Giessen, Germany,
²³ National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, USA,
²⁴ Center for Theranostics, Jagiellonian University, Krakow, Poland,
²⁵ Faculty of Engineering Sciences, Ghulam Ishaq Khan Institute of Engineering Sciences and Technology, Topi, Pakistan,
²⁶ Joint Department for Nuclear Physics, Lanzhou University and Institute of Modern Physics, Lanzhou, China,
²⁷ Research Center for Nuclear Physics, Osaka University, Osaka, Japan,
²⁸ Uppsala University, Uppsala, Sweden,
²⁹ Kyoto University, Kyoto, Japan,
³⁰ Ruhr-Universität Bochum, Institut für Experimentalphysik I, Bochum, Germany,
³¹ KEK, Tsukuba, Japan,
³² Saitama University, Sakura-ku, Japan,
³³ Tohoku University, Sendai, Japan,
³⁴ Peking University, Beijing, China,

^* e-mail: christophe.rappold@csic.es

Published online: 8 December 2023

Abstract

The current understanding of light hypernuclei, which are sub-atomic nuclei with strangeness, is being challenged and studied in detail by several European research groups and collaborations. In recent years, studies of hypernuclei using high-energy heavy ion beams have reported unexpected results on the three-body hypernuclear state ³_ΛH, named the hypertriton. For some time, reports of a shorter lifetime and larger binding energy than what was previously accepted have created a puzzling situation for its theoretical description; this is known as the "hypertriton puzzle". With the inclusion of the most recent experimental measurements, the current status of the hypertriton puzzle is evolving. Additionally, the possible neutral bound state of a Λ hyperon with two neutrons, nnΛ, has raised questions about our understanding of the formation of light hypernuclei either in bound or resonance states. These results have initiated several ongoing experimental programs all over the world to study these three-body hypernuclear states precisely. We are studying these light hypernuclear states by employing heavy ion beams at 2AGeV on a fixed carbon target with the WASA detector system and the Fragment Separator (FRS) at GSI. The WASA-FRS experimental campaign was performed during the first quarter of 2022, and this paper presents a short overview of the campaign and how it seeks to tackle the hypertriton and nnΛ puzzles. Data analysis is ongoing, and several preliminary results will be reported.