The strong elliptic flow seen at RHIC in non-central Au+Au collisions has been interpreted as a strong indication for early thermalization in a quark-gluon plasma state. The elliptic flow makes the collision zone expand more rapidly into the reaction plane than perpendicular to it. I show how pion interferometry as a function of the azimuthal
emission angle relative to the reaction plane allows to investigate the spatial and temporal consequences of elliptic flow. At energies
between RHIC and LHC the pion source at freeze-out is predicted to change from out-of-plane elongation to in-plane elongation. This can be anambiguously identified by a change of the azimuthal oscillation
pattern of the sideward HBT radius. The meaning of other features of the oscillation pattern will also be discussed.
Organiser(s): Yiota Foka, Guy Paic and Urs Wiedemann