High resolution spectroscopy of the “ΣN cusp” by using the d(K⁻, π⁻) reaction

We present a new proposal, J-PARC E90, to measure a missing-mass spectrum near the ΣN threshold for the d(K−, π−) reactions at 1.4 GeV/c. While many previous experiments support apparent enhancement near the ΣN thresh-old, the dynamical origin of this so-called “ΣN cusp” remains yet unsolved. The enhancement suggests either a cusp structure or a weakly bound state. One of the keys to making it clear is improving the missing-mass resolution and statistics. Our new experiment can achieve the missing-mass resolution of 0.4 MeV in σ using the K1.8 beam line and S-2S spectrometers at J-PARC. Further-more, we can suppress quasi-free background processes with the time projection chamber (HypTPC), which operated nicely for the H-dibaryon search experi-ment (J-PARC E42). The J-PARC E90 aims to extract the scattering length of the ΣN system with isospin T = 1/2 and spin-triplet channels.