High resolution Λ hypernuclei spectroscopy by the (e, e' K+) reaction

It is scheduled to run a Λ hypernuclear spectroscopy experiment (E01-011) by using (e, e' K+) reaction at Jefferson Laboratory in 2004. Based on the experience of E89-009, a newly developed K+ spectrometer (HKS) is planned to be installed on the K+ side and 'Tilt Method' is planned to be taken on the scattered electron side spectrometer. HKS is a high resolution K+ spectrometer designed for the (e, e' K+) reaction specifically. The tilt method, in which the whole spectrometer is tilted by 7.75 degrees vertically, reduces injection of both the bremsstrahlung electrons and the elastically scattered electrons while collects as many electrons as possible related to the virtual photons. Consequently, S/N ratio will be greatly improved and the hypernuclei yield is expected to increase by about fifty times compared to the last experiment by increasing both the incident beam intensity and the target thickness. Planned targets are p(e, e' K+) Λ, Σ, 12C(e, e' K+)Λ12B, 28Si(e, e' K+)Λ28Al and so on. It is contemplated that the highest energy resolution for the hypernuclei spectroscopy of a few hundred keV(FWHM) will be achieved by using the high quality electron beam of CEBAF and the high performance of HKS in combination. Status of the E01-011 preparation is described. (S. Funahashi)