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論文

Observation of a $$bar{K}NN$$ bound state in the $$^{3}$$He $$(K^-, Lambda p)n$$ reaction

山我 拓巳*; 橋本 直; 谷田 聖; 他66名*

Physical Review C, 102(4), p.044002_1 - 044002_14, 2020/10

 被引用回数:13 パーセンタイル:86.7(Physics, Nuclear)

We have performed an exclusive measurement of the $$K^{-}+! ~^{3}{rm He} to Lambda pn$$ reaction at an incident kaon momentum of $$1 {rm GeV}/c$$. In the $$Lambda p$$ invariant mass spectrum, a clear peak was observed below the mass threshold of $$bar{K}+N+N$$, as a signal of the kaonic nuclear bound state, $$bar{K}NN$$. The binding energy, decay width, and $$S$$-wave Gaussian reaction form-factor of this state were observed to be $$B_{K} = 42pm3({rm stat.})^{+3}_{-4}({rm syst.}) {rm MeV}$$, $$Gamma_{K} = 100pm7({rm stat.})^{+19}_{-9}({rm syst.}) {rm MeV}$$, and $$Q_{K} = 383pm11({rm stat.})^{+4}_{-1}({rm syst.}) {rm MeV}/c$$, respectively. The total production cross-section of $$bar{K}NN$$, determined by its $$Lambda p$$ decay mode, was $$sigma^{tot}_{K} cdot BR_{Lambda p} = 9.3pm0.8({rm stat.})^{+1.4}_{-1.0}({rm syst.}) mu{rm b}$$. We estimated the branching ratio of the $$bar{K}NN$$ state to the $$Lambda p$$ and $$Sigma^{0}p$$ decay modes as $$BR_{Lambda p}/BR_{Sigma ^{0}p} sim 1.7$$, by assuming that the physical processes leading to the $$Sigma N!N$$ final states are analogous to those of $$Lambda pn$$.

論文

Results of $$bar{K}NN$$ search via the $$(K^-, n)$$ 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 $$K^-pp$$ bound state. We performed an experiment to search for $$K^-pp$$ via the in-flight $$(K^-, n)$$ reaction at J-PARC. By studying $$Lambda p$$ invariant mass spectrum in the $$Lambda pn$$ final state and its dependence on momentum transfer of $$K^{-}N to bar{K}N$$, we observed a resonant state located below $$M_{K^{-}pp}$$. The mass and width of this resonant state are $$2324 pm 3(textit{stat}.)_{-3}^{+6}(textit{syst}.)$$ MeV/$$c^2$$, and $$115 pm 7(textit{stat}.)_{-20}^{+10}(textit{syst}.)$$ MeV, respectively, which can be naturally interpreted as a theoretically predicted $$K^-pp$$ bound state.

論文

Study of the elementary $$(K^-,n)$$ reactions to search for the $$bar{K}NN$$ bound state via the $$^3$$He$$(K^-,n)$$ reaction at J-PARC

山我 拓巳*; 谷田 聖; 他74名*

AIP Conference Proceedings 1735, p.040007_1 - 040007_6, 2016/05

 被引用回数:0 パーセンタイル:0.41

We have searched for the simplest kaonic nuclear state, $$bar{K}NN$$, using the in-flight $$^3$$He$$(K^-,n)$$ reaction at the J-PARC hadron experimental facility. In the semi-inclusive neutron missing-mass spectrum at $$theta_{n}^{rm lab}=0^{circ}$$, an excess of yield was observed just below the $$K^-pp$$ mass-threshold, which cannot be explained by any elementary reactions [PTEP 2015, 061D01]. To understand the missing-mass spectrum of $$^3$$He$$(K^-,n)X$$, we investigated the elementary $$(K^-,n)$$ reactions using hydrogen and deuterium targets. The $$p(K^-,n)X$$ missing-mass spectrum was well described by the charge-exchange reaction. However, in the $$d(K^-,n)X$$ spectrum, we observed an excess of yield just below the $$K^-p$$ mass-threshold, which was similar to that in the $$^3$$He$$(K^-,n)X$$ spectrum.

論文

Spectroscopic study of hyperon resonances below $$bar{K}N$$ threshold via the $$(K^-,n)$$ reaction on deuteron

山我 拓巳*; 谷田 聖; J-PARC E31 Collaboration*; 他70名*

JPS Conference Proceedings (Internet), 8, p.021016_1 - 021016_5, 2015/09

We are planning to carry out an experimental study of hyperon resonance via the $$d(K^-,n)$$ reaction using kaon beam which has momentum of 1 GeV/$$c$$ at the J-PARC hadron experimental facility. In the presented reaction, $$Lambda(1405)$$ can be produced dynamically from meson-baryon resonant state. The performance of the counters was tested at the previous beam time of the J-PARC. The counters worked as expected. The preparation of experimental setup had been done.

口頭

Development of large acceptance spectrometer for systematic study of kaonic nuclei at J-PARC

七村 拓野; 橋本 直; 佐久間 史典*; 山我 拓巳*; 岩崎 雅彦*

no journal, , 

反K中間子と核子のアイソスピン0の状態に働く強い引力によって生み出される$$Lambda$$(1405)や反K中間子原子核は、ストレンジネスを持つ系の中でも特徴的なもののひとつである。多くの実験が最も軽い反K中間子原子核である"$$K^- pp$$"状態の存在を確立しようとしてきたが、明確な結論は得られていなかった。近年、J-PARC E15実験が"$$K^- pp$$"状態を探索する実験を、in-flight $$K^- +^3$$He反応と、$$Lambda p n$$終状態のexclusive解析を用いて行った。これにより$$Lambda p$$系の不変質量だけでなく、$$Lambda p$$系への運動量以降も再構成することにより、"$$K^- pp$$"状態であると解釈できるイベントを数多く同定した。それだけでなく、"$$K^- pp$$"状態の大きさが小さいことが示唆され、このことは反K中間子原子核の密度が通常原子核よりも大きくなっていることを意味する結果であり非常に興味深い。この成功した実験手法をより重い反K中間子原子核、$$bar{K}NNN, bar{K}NNNN,dots$$に適用する、あるいは$$bar{K}NN$$状態の基本的な性質の研究を行うために、我々は新たな磁気スぺクトロメータを開発中である。exclusive解析は反K中間子原子核からの崩壊粒子をできるだけ多く検出することが必要なため、新しいスぺクトロメータは現在のものよりも1.6倍大きい93%の立体角を持たせる。それを実現するために、超電導ソレノイド電磁石や円筒型ドリフトチェンバーや荷電粒子/中性子検出器は3mから4mの長さのものを作る必要がある。本発表では、新スぺクトロメータを構成する要素と開発状況を報告する。新スぺクトロメータを用いる物理実験についても紹介する。

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