Summary of the K⁻pp bound-state observation in E15 and future prospects

¹ RIKEN Cluster for Pioneering Research, RIKEN, Wako 351-0198, Japan
² Research Center for Nuclear Physics (RCNP), Osaka University, Osaka 567-0047, Japan
³ Department of Physics, Osaka University, Osaka 560-0043, Japan
⁴ Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia V8W 3P6, Canada
⁵ Department of Physics, Seoul National University, Seoul 151-742, South Korea
⁶ National Institute of Physics and Nuclear Engineering - IFIN HH, Bucharest, Romania
⁷ Stefan-Meyer-Institut für subatomare Physik, A-1020 Vienna, Austria
⁸ Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Torino, Torino, Italy
⁹ Dipartimento di Fisica Generale, Universita’ di Torino, Torino, Italy
¹⁰ Laboratori Nazionali di Frascati dell’ INFN, I-00044 Frascati, Italy
¹¹ High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
¹² Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan
¹³ Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
¹⁴ Laboratory of Physics, Osaka Electro-Communication University, Osaka 572-8530, Japan
¹⁵ ASRC, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan
¹⁶ Department of Physics, Kyoto University, Kyoto 606-8502, Japan
¹⁷ Technische Universität München, D-85748, Garching, Germany
¹⁸ Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan
¹⁹ Research Center for Electron Photon Science (ELPH), Tohoku University, Sendai 982-0826, Japan
²⁰ Engineering Science Laboratory, Chubu University, Aichi 487-8501, Japan
²¹ Centro Ricerche Fermi-Museo Storico della Fisica e Centro studi e ricerche “Enrico Fermi”, 000184 Rome, Italy
²² Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan
²³ Institute for Chemical Research, Kyoto University, Kyoto 611-0011, Japan

^* e-mail: sakuma@ribf.riken.jp

Published online: 27 April 2022

Abstract

The possible existence of deeply-bound $\bar K$$\overline{K}$-nuclear bound states, kaonic nuclei, has been widely discussed as products of the strongly attractive $\bar K$$\overline{K}$N interaction in I = 0 channels. Investigations of those exotic states will provide us unique information of the $\bar K$$\overline{K}$N interaction below the threshold, which is still not fully understood so far. Recently, we observed the simplest kaonic nuclei, $\bar K$$\overline{K}$NN, having a much deeper binding energy than normal nuclei via inflight (K⁻, N) reactions at the J-PARC E15 experiment. For further studies, we have proposed a series of experimental programs for the systematic investigation of light kaonic nuclei, from $\bar K$$\overline{K}$N (Λ(1405)) to $\bar K$$\overline{K}$NNNN. We will measure the $\bar K$$\overline{K}$NNN (A = 3) system at the new experiment approved as J-PARC E80, as a first step toward a comprehensive study.