Experiment on Positronium Invisible decay Channels (EPIC)

Positronium, being a particle - anti-particle system, is a very sensitive probe to new interactions beyond the Standard Model. In particular, the triplet state of Ps with parallel spins, ortho-positronium (oPs), can be used to search for New Physics beyond the Standard Model such as Hidden Sectors, Extra dimensions or milli-charged particles.

In particular we are currently testing a specifc class of Hidden Sector in which the mediator is massless. This is so called the Mirror Matter model, which states that each ordinary particle has a mirror twin with the same properties (e.g. mass and charge) but opposite chirality. Such a mirror sector would provide an explanation of parity violation and it is a very good candidate for dark matter, being mirror particles naturally stable and massive. The model also allows interactions between colourless, neutral particles (e.g. photons and mirror photons) which could lead to oPs oscillations into mirror–oPs. Such an oscillation would result in a photon-less decay of oPs (as opposed to the usual 3-photon decay totalling 1.022 MeV), whose experimental signature is events with missing energy. Our goal is to improve the sensitivity of such a search compared to our previous results by two orders of magnitude in order to cover an interesting region well motivated theoretically and that cannot be excluded by astrophysical observations.