An experiment with a newly developed high-resolution kaon spectrometer (HKS) and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab (JLab). The ground state of a neutron-rich hypernucleus,

A pioneering experiment in Λ hypernuclear spectroscopy, undertaken at the Thomas Jefferson National Accelerator Facility (Jlab), was recently reported. The experiment used the high-precision, continuous electron beam at Jlab, and a special arrangement of spectrometer magnets to measure the spectrum from nat C and 7 Li targets using the (e, e ′ K + ) reaction. The 12 Λ B spectrum was previously published. This experiment is now reported in more detail, with improved results for the 12 Λ B spectrum. In addition, unpublished results of the 7 Λ He spectrum are also shown. This later spectrum indicates the need for a more detailed few-body calculation of the hypernucleus and the reaction process. The success of this experiment demonstrates that the (e, e ′ K + ) reaction can be effectively used as a high resolution tool to study hypernuclear spectra, ant its use should be vigorously pursued.

High energy CW electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the usefulness of the (e,e ′ K + ) reaction. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed resolution, ∼ 900 keV, of the 12 Λ B spectrum is the best yet attained using magnetic spectrometers. The positions of the major excitations are in agreement with theoretical predictions and the previous binding energy measurements.

Since the pioneering experiment, E89-009 studying hypernuclear spectroscopy using the (e, e K + ) reaction was completed, two additional experiments, E01-011 and E05-115, were performed at Jefferson Lab. These later experiments used a modified experimental design, the "tilt method", to dramatically suppress the large electromagnetic background, and allowed for a substantial increase in luminosity. Additionally, a new kaon spectrometer, HKS (E01-011), a new electron spectrometer, HES and a new splitting magnet (E05-115), were added to produce new data sets of precision, highresolution hypernuclear spectroscopy. All three experiments obtained a spectrum for B 12 Λ , which is the most characteristic p-shell hypernucleus and is commonly used for calibration. Independent arXiv:1406.2353v2 [nucl-ex] 13 Aug 2014 2 analyses of these different experiments demonstrate excellent consistency and provide the clearest level structure to date of this hypernucleus as produced by the (e, e K + ) reaction. This paper presents details of these experiments, and the extraction and analysis of the observed B 12 Λ spectrum.

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