High resolution spectroscopy of the "N cusp" at J-PARC (J-PARC P90)

Ichikawa, Yudai   

Recently, we have proposed a new experiment (J-PARC P90 experiment) to measure the missing-mass spectrum around the threshold in the d(K, ) reaction at 1.4 GeV/c. A clear enhancement was observed near the N threshold, so called "N cusp", for a long time ago. However, the dynamical origin of this enhancement remains unclear as yet. Especially, whether "N cusp", is cusp or unstable bound state has not been determined yet. One of the key to make it clear is to improve the missing-mass resolution and statistics. In this experiment, we can achieve the missing-mass resolution of 0.4 MeV in by using K1.8 beam line and S-2S spectrometers at J-PARC. Moreover, we will additionally install the time projection chamber (HypTPC), which was developed for the other J-PARC experiment (E42: H-dibaryon search), to suppress quasi-free backgrounds by detecting the charged tracks of the decay products. We can deduce the scattering length of N system with isospin T = 1/2 and spin triplet channel in this experiment.