Speaker
Description
Recently, we have proposed a new experiment (J-PARC P90 experiment) to measure the missing-mass spectrum around the $\Sigma N$ threshold in the $d(K^-, \pi^-)$ reaction at 1.4 GeV/$c$. A clear enhancement was observed near the $\Sigma N$ threshold, so called "$\Sigma N$ cusp", for a long time ago. However, the dynamical origin of this enhancement remains unclear as yet. Especially, whether "$\Sigma N$ 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 $\sigma$ 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 $\Sigma N$ system with isospin T = 1/2 and spin triplet channel in this experiment. In this presentation, we will show the detailed information of this new experiment.
