Status of Λn interaction study via the final state interaction effect in γd → K⁺Λn production

The studies of Baryon interaction including strangeness have been mainly carried by Hypernuclear experiment, because of difficulties of the hyperon-nucleon (YN) scattering. The recent results of _Λ⁴H and _Λ⁴He measurements show the existing of a large charge symmetry breaking (CSB) in ΛN interaction. It is suggested that the ΛN CSB is due to ΛΣ coupling in ΛN interaction. On the other hand, there is lack of precise data in the Λn interaction. The measurement of ΛN interaction is one of the key issues in the strangeness nuclear physics. The Λn interaction can be extracted by comparing cross-sections of γd → K⁺Λn and γp → K⁺Λ due to the final state interaction (FSI) effect of Λn. We have been investigating strangeness photoproduction with tagged photon beam in Research Center for Electron Photon Science (ELPH), Tohoku University. The spectrometer, NKS2, was originally designed for the measurement of K⁰Λ production. Upgrades of NKS2 detectors for the Λn FSI experiment are in progress: high resolution TOF counter by Multi-gap Resistive Plate Chamber and Electron Veto by Aerogel Cherenkov counter. (author)