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reaction at J-PARC山我 拓巳*; 橋本 直; 谷田 聖; 他66名*
JPS Conference Proceedings (Internet), 26, p.023008_1 - 023008_6, 2019/11
There is a long-standing argument of the existence of kaonic nucleus, which is a bound state of anti-kaon and nucleus. Theoretically, its existence is strongly supported, however its binding energy and width have not been established yet. It is strongly desired to have an experiment to investigate the simplest kaonic nucleus, so-called 
bound state. We performed an experiment to search for via the in-flight reaction at J-PARC. By studying 
invariant mass spectrum in the 
final state and its dependence on momentum transfer of 
, we observed a resonant state located below 
. The mass and width of this resonant state are 
MeV/
, and 
MeV, respectively, which can be naturally interpreted as a theoretically predicted bound state.
橋本 直
no journal, ,
An antikaon, the lightest meson with a strange quark, is a unique candidate for forming a nuclear-bound state because the K
N interaction is known to be strongly attractive. Such an exotic state with a meson as a constituent particle has been searched for many years, but no conclusive result has been obtained so far. We have investigated the KNN system, the simplest kaonic nucleus consisting of one antikaon and two nucleons, using an in-flight K
beam on helium-3 in J-PARC E15. We exclusively analyzed Lambda-p pairs, decay products of KNN, with a requirement of a missing neutron and found a clear peak structure below the KNN binding threshold. Since this peak position is independent of the momentum transfer to the KNN system, we interpreted it as evidence of the kaonic nuclear-bound state. Very recently, we also took a small amount of data with a helium-4 target as J-PARC T77 and found a sub-threshold peak structure in the Lambda-d invariant-mass distribution, which could be signals of KNNN. Another approach is to evaluate the basic KN interaction better. Especially, X-ray spectroscopy of kaonic atoms is essential to have established the strongly attractive interaction. In this direction, we have recently succeeded in dramatically improving the precision of X-ray measurements from kaonic helium atoms in J-PARC E62 using a novel cryogenic detector, TES. In this contribution, we will discuss an overview of above experimental results and future prospects for the systematic study of kaonic systems.
bound state in the 
final states of the in-flight 
reaction on 
He橋本 直
no journal, ,
In recent years, the possible existence of deeply-bound 
nuclear bound states has been widely discussed as a consequence of the strongly attractive 
interaction in I = 0 channels. Very recently, J-PARC E15 experiment reported an observation of the simplest kaonic nuclei, 
, in the invariant-spectrum of the in-flight reaction on helium-3. Observation of other kaonic nuclei would provide a further support for the existence of such exotic states. Furthermore, mass-number dependence of kaonic nuclear systems would be of great importance to study interplay between the attraction and the 
repulsion at short distances. We collected -induced data on helium-4 as a feasibility test of a lifetime measurement of light hypernuclei (J-PARC T77) in June 2020. In this contribution, we would like to present the latest results of the analysis, and discuss future prospects towards more comprehensive investigation of the system.
