Evolution of octupole deformation and collectivity in neutron-rich lanthanides

The onset of octupole deformation and its impact on related spectroscopic properties is studied in even-even neutron-rich lanthanide isotopes Xe, Ba, Ce, Nd with neutron number $86\leqslant N\leqslant 94$. Microscopic input comes from the Hartree-Fock-Bogoliubov approximation constrains axially symmetric quadrupole operators using Gogny-D1M interaction. At mean-field level, reflection asymmetric ground states are predicted for around $N=88$. Spectroscopic by diagonalizing interacting boson model Hamiltonian, parameters obtained via mapping potential energy surface onto expectation value Hamiltonian $s$, $d$, $f$ condensate state. results low-energy positive- negative-parity excitation spectra as well electric dipole, quadrupole, transition probabilities indicate pronounced octupolarity $Z\approx 56$ $N\approx 88$ nuclei.