A fiber detector to monitor ortho-Ps formation and decay

We describe a novel method to use a scintillating fiber detector similar to the Fast Annihilation Cryogenic Tracking (FACT) used at the antimatter experiment AEḡIS to monitor the presence of ortho-positronium. A single scintillating fiber was coupled to a photomultiplier tube and irradiated by flashes of about 6 <math display="inline" id="d1e518" altimg="si8.svg"><mo>×</mo></math> 10<sup loc="post">6</sup> gamma quanta with 511keV energy, produced by approximately 10ns long positron pulses. The results were used to demonstrate the ability to track the creation and annihilation of ortho-positronium atoms over time in cryogenic and highly magnetic environments by using the FACT detector as a “digital calorimeter”.