Strength Functions for Photoproduction of Medium-Mass Hypernuclei

Strength functions have been calculated for the photoproduction of $\Lambda$-hypernuclei by choosing typical medium-mass nuclear targets such as $^{28}$Si, $^{40}$Ca, and $^{52}$Cr. The DWIA framework has been adopted together with the modern amplitudes for the elementary $\gamma p\rightarrow \Lambda K^+$ process. For the targets with surface proton $jj$-closed orbit (or the similar situation), the unnatural parity high-spin states such as $4^-$, $5^+$, $6^-$ and $7^+$ are selectively excited due to the spin-flip dominant character of the elementary amplitudes. On the other hand, for the proton LS-closed target ($^{40}$Ca), natural parity high-spin states are excited as well. In both cases, it is important to obtain well-separated clear spectra. The nuclear level fragmentation caused by the one-proton annihilation is taken into account. The theoretical spectrum predicted for the first target ($^{28}$Si) proved to be in very good agreement with the result of recent analysis for the $^{28}$Si$(e,e'K^+)^{28}_{\Lambda}$Al experiment done at JLab. Thus predictions for the latter two targets seem to give the promising and reliable spectra to encourage further extention of the $(e,e'K^+)$ experiments. Novel aspects of medium-mass hypernuclear spectroscopy will be discussed.