Observation of Hypernuclear Gamma-Ray Transitions inLiΛ7andBeΛ9

$\gamma$-ray transitions of energy 2.034 ± 0.023 MeV in the hypernucleus ${}_{\Lambda }{}^7{}_{}{}^{}\mathrm{Li}$ and 3.079 ± 0.040 MeV in the hypernucleus ${}_{\Lambda }{}^9{}_{}{}^{}\mathrm{Be}$ are observed. In both cases, the energy of the $\gamma$ ray in the hypernucleus ${}_{\Lambda }{}^A{}_{}{}^{}Z$ is very close to the energy of the first excited state of the nuclear core. The $\gamma$ rays are interpreted as arising from core transitions in the presence of the $\Lambda$ particle. The size of the shift places limits on the strength of the $\Lambda N$ spin-dependent interaction.