Λ polarization measurement of the π − p → K 0 Λ reaction in J-PARC E40 experiment

We performed the J-PARC E40 experiment to measure the Σ p scattering cross sections from 2018 to 2020. Together with the π − p → K + Σ − data, the π − p → K 0 Λ data were accumulated as a byproduct. The analysis confirmed that Λ could be identified with an S/N ratio of ∼ 2.67. The polarization of Λ( P Λ ) was preliminarily derived as 1.009 ± 0.049 for the K 0 angular range of 0.7 < cos θ K 0 , CM < 0.8. It is more accurate than the past data [1]. The high polarization enables us to measure not only the differential cross section but also spin observables of the Λ p scattering in the future J-PARC experiment.