First search for invisible decays of ortho-positronium confined in a vacuum cavity

TL;DR

This paper reports the first experimental search for invisible decays of ortho-positronium confined in a vacuum cavity, setting new limits on decay probabilities and kinetic mixing with mirror matter, relevant for dark matter models.

Contribution

It presents the first vacuum-based search for invisible o-Ps decays, providing new upper limits on decay branching ratio and photon kinetic mixing, free from matter collision systematic effects.

Findings

No evidence of invisible decays was observed.

Upper limit on branching ratio: < 5.9×10^{-4} (90% C.L).

Upper limit on kinetic mixing: < 3.1×10^{-7} (90% C.L).

Abstract

The experimental setup and results of the first search for invisible decays of ortho-positronium (o-Ps) confined in a vacuum cavity are reported. No evidence of invisible decays at a level $\text{Br}\left(\text{o-Ps}\to\text{invisible}\right) < 5.9\times 10^{-4}$ (90% C. L.) was found. This decay channel is predicted in Hidden Sector models such as the Mirror Matter (MM), which could be a candidate for Dark Matter. Analyzed within the MM context, this result provides an upper limit on the kinetic mixing strength between ordinary and mirror photons of $\epsilon < 3.1 \times 10^{-7}$ (90% C. L.). This limit was obtained for the first time in vacuum free of systematic effects due to collisions with matter.