### Positronium Portal to the Mirror World.

Paolo Crivelli
It was realized sometime ago by Glashow that the mirror matter could have a portal to our world through photon-mirror photon mixing ($\epsilon$) which would lead to orthopositronium (oPs) to mirror orthopositronium oscillations. This would result in a modification of the oPs decay rate however this effect is too small to be observed. Another experimental signature of this process is the apparently invisible decay of oPs. In this paper, we describe an experiment to search...