[en] We report on the design and commissioning of two silica aerogel Cherenkov detectors with different refractive indices. In particular, extraordinary performance in terms of the number of detected photoelectrons was achieved through an appropriate choice of PMT type and reflector, along with some design considerations. After four years of operation, the number of detected photoelectrons was found to be noticeably reduced in both detectors as a result of contamination, yellowing, of the aerogel material. Along with the details of the set-up, we illustrate the characteristics of the detectors during different time periods and the probable causes of the contamination. In particular we show that the replacement of the contaminated aerogel and parts of the reflecting material has almost restored the initial performance of the detectors.

[en] The HKS (Jlab E01-011) experiment on spectroscopy of Lambda-hypernuclei using (e,e'K+) reaction was successfully carried out in 2005. This paper gives a brief description of the experiment and its technique and shows some of the preliminary spectra that are still under analysis.

[en] An experimental study of the 16O(e, e'K+)16N_#Lambda# reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e, e'K+)Λ,Σ₀ exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76 ± 0.16 MeV was obtained for 16N_#Lambda# with better precision than previous measurements on the mirror hypernucleus 16O_#Lambda#. Precise energies have been determined for peaks arising from a Lambda in s and p orbits coupled to the p1/2 and p3/2 hole states of the 15N core nucleus.