Coexistence of transverse and longitudinal wobbling modes in $^{187}$Au*

Nuclear wobbling motion has been investigated in the $^{187}$Au nucleus. The $^{174}$Yb($^{19}$F,6n)$^{187}$Au reaction was used to populate the levels of interest using the Gammasphere array. Detailed analysis has revealed two separate wobbling bands built on $(\pi h_{9/2})^{1}$ and $(\pi h_{11/2})^{-1}$ configurations. The wobbling nature of these bands has been verified by angular distribution measurements showing a $\Delta$I = 1, E2 nature of the $n_{\omega + 1}\to n_{\omega}$ transitions. Most interestingly, the two structures have been found to exhibit different types of wobbling: transverse and longitudinal. $^{187}$Au is the case of the first cleanly established longitudinal wobbler and of the coexistence of both forms of wobbling, a phenomenon never observed before. Particle Rotor Model calculations have been found to be in good agreement with the experiment.