Search for K meson nuclei using π meson beams

The authors conducted a search experiment at J-PARC on the simplest K-meson nucleus K-pp, using (π⁺,K⁺) reaction in liquid deuterium target. As a result of the inclusive reaction analysis, in which only (π⁺,K⁺) is measured, ΣN cusp was detected with a mass resolution more than twice as high as that in the past experiments. A theoretical study that takes this data into account is expected to advance the research on ΣN-ΛN conversion power. In the generation region of Λ(1405) and Σ(1385) in the quasi-free process, the authors found that the peak centers of experimental data and simulation are deviated by about 30 MeV/c². Although this gap may be due to the interaction between Λ(1405)N or Σ(1385)N, follow-up experiments and theoretical research are indispensable for clear cause investigation. From the results of the measurement of (π⁺,K⁺), as well as the coincidence analysis that detected protons (proton pairs) using a range detector installed on the side of the target, a broad structure was detected in the vicinity of 2.3 GeV/c². Assuming that this structure is K^-_pp, the binding energy corresponds to about 100 MeV. Since it is difficult to theoretically explain this large binding energy, it may have been caused by other conditions such as strange dibaryon. (A.O.)