Evidence for Octupole Vibration in the Triaxial Superdeformed Well Oflu164

High-spin states in Lu-164 were populated in the Sb-121(Ca-48,5n) reaction at 215 MeV and gamma-ray coincidences were measured with the Gammasphere spectrometer. Through this experiment the eight known triaxial superdeformed bands in Lu-164 could be confirmed. Some of these bands were extended to higher as well as to lower spins. Evidence is reported for the first time for weak Delta I=1,E1 transitions linking TSD3 and TSD1. This observation may imply coupling to octupole vibrational degrees of freedom. The decay mechanism is different from the one observed in the neighboring even-N isotopes, which exhibit wobbling excitations built on the pi i(13/2) structure with E2(M1),Delta I=1 interband decay. An additional sequence decaying at high spin into TSD1 was observed up to I-pi=(50(-)). This band has a constant dynamic moment of inertia of similar to 70h(2)MeV(-1) and an alignment that is similar to 2h larger than that found for TSD1. A revision of the assumed spin-parity-assignment of TSD2 is based on the observed decay-out to normal-deformed structures. The parity and signature quantum numbers of TSD2 are now firmly assigned as (pi,alpha)=(+,0), in disagreement with the former assignment of (pi,alpha)=(-,1), which was based on the assumption that TSD2 is the signature partner of TSD1. TSD1 and TSD2 show an alignment gain at h omega similar to 0.67 and 0.60 MeV, respectively. In TSD1 the involvement of the j(15/2) neutron orbital is suggested to be responsible for the high-frequency crossing.