Production of the “K−pp”-like structure in the d(π+,K+) reaction at 1.69 GeV/c

We have investigated the π++d→K++Xπ++d→K++X reaction at 1.69 GeV/c   at the hadron experimental hall of J-PARC. Systems with baryon number B=2B=2 and strangeness S=−1S=−1 are produced in this reaction. Owing to the very wide momentum acceptance of the spectrometer, we were able to search from the ΛN   threshold to above the K¯NN threshold, which covers the energy region where the K−ppK−pp bound state and/or the Σ(1385)NΣ(1385)N bound state could show up.We observed a significant shift of the quasi-free Σ(1385)/Λ(1405)Σ(1385)/Λ(1405) production peak by approximately 30 MeV to the lighter mass side. Further, with the coincidence of two protons in the final state, a broad bump structure was observed with a mass and width of 2275−18+17(stat.)−30+21(syst.) MeV/c2 and 162−45+87(stat.)−78+66(syst.) MeV coming from the K−pp→Σ0+pK−pp→Σ0+p decay.