2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/37669We propose an experiment to search for invisible decays of orthopositronium (o-Ps) with a 90% confidence sensitivity in the branching ratio as low as $10^{-8}$. Evidence for this decay mode would unambigously signal new physics: either the existence of extra--dimensions or fractionally charged particles or new light gauge bosons. The experimental approach and the detector components of the proposed experiment are described.Based on a talk given at Workshop on Positronium Physics, Zurich, Switzerland, 30-31 May 2003High Energy Physics - Experimenttext