Hypernucleus and γray spectroscopy experiments

This paper consists on two parts, the first part is introduction of hypernucleus and the second one γray spectroscopy experiments of Λ hypernucleus. Hypernucleus indicates new interactions and new phenomena depend on strangeness, new freedom. The γray spectroscopy becomes a very strong method to research the hypernucleus structure using the large energy resolution. KEK-PS E419 experiment was a simultaneous measurement of γrays from 7ΛLi hypernucleus produced by 7Li(π+, K+) reaction. The γray spectrum has two peaks such as 690 keV and 2050 keV, which were assigned to M1(3/2+ →1/2+) and E2(5/2+→1/2+), respectively. The former peak was 691.7±0.7 ±1.0 KeV, which value showed Δ parameter was about 0.5 MeV , strength of the spin-spin force. From the shape of E2 transition peak, life time of parent level (5/2+) was determined as 5.8+0.9-0.7±0.7 ps. This value was 1/3 times of B(E2;3+→1+) of 6Li. So that, it indicated 7ΛLi shrinked much more than 6Li. (S.Y.)