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

Abstract

We have performed an exclusive measurement of the $K^{-}+{}^3\mathrm{He}\to \Lambda pn$ reaction at an incident kaon momentum of $1\mathrm{GeV}/c$.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 $B_K=42\pm 3(stat.{)}_{-4}^{+3}(syst.)\mathrm{MeV}$, ${\Gamma }_K=100\pm 7(stat.{)}_{-9}^{+19}(syst.)\mathrm{MeV}$, and $Q_K=383\pm 11(stat.{)}_{-1}^{+4}(syst.)\mathrm{MeV}/c$, respectively. The total production cross-section of $\bar{K}NN$, determined by its $\Lambda p$ decay mode, was ${\sigma }_K^{tot}\cdot B{R}_{\Lambda p}=9.3\pm 0.8(stat.{)}_{-1.0}^{+1.4}(syst.)\mu \mathrm{b}$.We estimated the branching ratio of the $\bar{K}NN$ state to the $\Lambda p$ and ${\Sigma }^{0}p$ decay modes as $B{R}_{\Lambda p}/B{R}_{{\Sigma }^{0}p}\sim 1.7$, by assuming that the physical processes leading to the $\Sigma NN$ final states are analogous to those of $\Lambda pn$.

arXiv comment13 pages, 12 figures

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• 50 Years of Quantum Chromodynamics
• Cross-channel constraints on resonant antikaon-nucleon scattering
• Chiral symmetry restoration at high matter density observed in pionic atoms
• Pole position of $\Lambda (1405)$ measured in $d(K^{-},n)\pi \Sigma$ reactions
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• Feasibility of an experimental search for a resonance of a pion and a light nucleus