An event excess observed in the deeply bound region of the 12C (<i>K</i>−, <i>p</i>) missing-mass spectrum

Abstract We have measured, for the first time, the inclusive missing-mass spectrum of the $^{12}$C$(K^-, p)$ reaction at an incident kaon momentum of 1.8 GeV/$c$ at the J-PARC K1.8 beamline. We observed a prominent quasi-elastic peak ($K^-p \rightarrow K^-p$) in this spectrum. In the quasi-elastic peak region, the effect of secondary interaction is apparently observed as a peak shift, and the peak exhibits a tail in the bound region. We compared the spectrum with a theoretical calculation based on the Green’s function method by assuming different values of the parameters for the $\bar{K}$–nucleus optical potential. We found that the spectrum shape in the binding-energy region -300 \, \text{MeV} &lt; B_{K} &lt; 40 MeV is best reproduced with the potential depths $V_0 = -80$ MeV (real part) and $W_0 = -40$ MeV (imaginary part). On the other hand, we observed a significant event excess in the deeply bound region around $B_{K} \sim 100$ MeV, where the major decay channel of $K^- NN \to \pi\Sigma N$ is energetically closed, and the non-mesonic decay modes ($K^- NN \to \Lambda N$ and $\Sigma N$) should mainly contribute. The enhancement is fitted well by a Breit–Wigner function with a kaon-binding energy of 90 MeV and width 100 MeV. A possible interpretation is a deeply bound state of a $Y^{*}$-nucleus system.</jats:p

J-PARC E27 Experiment to Search for a K−pp Bound State

We have carried out an experimental search for the simplest kaonic nucleus, $K^{ - }pp$, by using the $d(\pi ^{ + },K^{ + })$ reaction at $p_{\pi ^{ + }}$ = 1.69 GeV/$c$. The differential cross section of this reaction with covering a wide missing-mass range from the $\Lambda$ production threshold to the $\Lambda (1405)/\Sigma (1385)$ region has been measured for the first time. The inclusive missing-mass shape of the $\Lambda$ and $\Sigma$ production region was understood with a simple quasi-free picture except for an enhancement at 2.13 GeV/$c^{2}$ due to a $\Sigma N$ cusp. An obtained peak attributed to $Y^{*}$ production was significantly shifted to the low mass side compared with the simulation by $- 22.4$ MeV/$c^{2}$

A Σp\Sigma p scattering Experiment at J-PARC and the Analysis Status

International audienceJ-PARC E40 aims to measure the differential cross sections of the Σ^±p elastic scatterings and the Σ^−p → Λn conversion. A clear peak of Σ^− was observed in a missing mass spectrum of the π^−p → K^+X reaction and recoil protons from the πp elastic scattering were successfully observed in the data taken in the summer 2018. The rest of data taking is coming in the spring 2019