Observation of the Helium 7 {Lambda} hypernucleus by the (e,e'K+) reaction

An experiment with a newly developed high-resolution kaon spectrometer (HKS) and a scattered electron spectrometerwith a novel configuration was performed in Hall C at Jefferson Lab (JLab). The ground state of a neutron-rich hypernucleus, He 7 { Lambda}, was observed for the first time with the (e,e'K+) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The He 7 { Lambda} binding energy suppliesthe last missing information of the A=7, T=1 hypernuclear iso-triplet, providing a new input for the charge symmetry breaking (CSB) effect of { Lambda} N potential.