This book presents an experiment at J-PARC E15 experiment, which explores an strangeness S = -1 dibaryonic state in the 1.0GeV/c K− beam on a Helium-3 target, together with the first demonstration of multi-nucleon absorption processes of K− in in-flight reactions. The book describes the successful identification of two components using the Dalitz plot of K−ppn → Λ+p+n events. One is widely and uniformly distributed in the three-body phase space, which provides the first evidence of genuine three-nucleon absorption following the three-body phase space. The second is concentrated at specific neutron energy in the forward direction in a low momentum transfer to the Λp system, which is found to imply a weakly bound K̄NN state.
Providing an overview of the J-PARC apparatus, beam line, detectors and data acquisition system, it is a valuable source for the readers interested in large-scale accelerator facilities. Further, it comprehensively reviews the data analysis to offer insights into how the dibaryonic states are experimentally demonstrated.