Highly deformed band structures due to core excitations in 123 Xe

High-spin states in $^{123}\mathrm{Xe}$ were populated in the $^{80}\mathrm{Se}(^{48}\mathrm{Ca}, 5\mathrm{n})^{123}\mathrm{Xe}$ reaction at a beam energy of 207 MeV. $\ensuremath{\gamma}$-ray coincidence events were recorded with the Gammasphere spectrometer. Four new high-spin bands have been discovered in this nucleus. The bands are compared with those calculated within the framework of cranked Nilsson-Strutinsky and cranked Nilsson-Strutinsky-Bogoliubov models. It is concluded that the configurations of the bands involve two-proton excitations across the $Z=50$ as well as excitation of neutrons across the $N=82$ shell gaps resulting in a large deformation, ${\ensuremath{\varepsilon}}_{2}\ensuremath{\approx}0.30$ and $\ensuremath{\gamma}\ensuremath{\approx}{5}^{\ensuremath{\circ}}$.