High-resolution spectroscopy of neutron-rich Br isotopes and signatures for a prolate-to-oblate shape transition at N=56

The first systematic experimental study of the neutron-rich Br isotopes with two complementary state-of-the-art techniques is presented. These isotopes have been populated in the fission process at two different facilities, GANIL and ILL. New spectroscopic information has been obtained for odd-even ${}^{87-93}$Br isotopes and the experimental results have been compared with state-of-the-art Large-Scale Shell-Model and DNO Shell-Model calculations. As a result of such theoretical approaches, a transition from prolate (${}^{87,89}$Br) to oblate (${}^{91,93}$Br) shapes is obtained from the subtle balance between proton and neutron quadrupole deformations, as a clear signature of pseudo-SU3 quadrupole regime.