Observation of the "$K^{-}pp$"-like structure in the $d({\pi }^{+},K^{+})$ reaction at 1.69 GeV/$c$

Abstract

We have observed a "$K^{-}pp$"-like structure in the $d({\pi }^{+},K^{+})$ reaction at 1.69 GeV/$c$. In this reaction $\Lambda (1405)$ hyperon resonance is expected to be produced as a doorway to form the $K^{-}pp$ through the ${\Lambda }^{\ast }p\to K^{-}pp$ process. However, most of the produced $\Lambda (1405)$'s would escape from deuteron without secondary reactions. Therefore, coincidence of high-momentum ($>$ 250~MeV/$c$) proton(s) in large emission angles ($39^{\circ }<{\theta }_{lab.}<122^{\circ }$) was requested to enhance the signal-to-background ratio. A broad enhancement in the proton coincidence spectra are observed around the missing-mass of 2.27 GeV/$c^2$, which corresponds to the $K^{-}pp$ binding energy of 95 ${}_{-17}^{+18}$ (stat.) ${}_{-21}^{+30}$ (syst.) MeV and the width of 162 ${}_{-45}^{+87}$ (stat.) ${}_{-78}^{+66}$ (syst.) MeV.

arXiv comment8 pages, 4 figures, submitted to PTEP

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