Positronium decay into a photon and neutrinos

Abstract

We determine the rates and energy and angular distributions of the positronium decays into a photon and a neutrino-antineutrino pair, Ps → γν ν . We find that both positronium spin states have access to this decay channel, contrary to a previously published result. The low-energy tails of the spectra are shown to be sensitive to the binding effects and agree with Low's theorem. Additionally, we find a connection between the behaviour of the soft photon spectrum in both o-Ps → γν ν and o-Ps → 3γ decays, and the Stark effect.

First search for invisible decays of orthopositronium confined in a vacuum cavity

“…Note that, within the SM, photonless (and thus invisible) decays of both o-Ps and p-Ps into neutrinos are mediated by the weak interaction and are heavily suppressed with a branching ratio below 10 −17 due to the small mass of the positronium atom [37,38]. The above calculations do not consider incoherent processes (e.g.…”

QED and Fundamental Symmetries in Positronium Decays

“…For example, the three photon decay of p-Ps is forbidden in QED but can occur through weak interactions involving a W-boson loop with branching ratio BR(p-Ps → 3γ) = 4.4 × 10 −77 [51]. Tiny branching ratios are found for decays into a photon and two neutrinos [52], less than about 10 −21 for o-Ps and 10 −24 for p-Ps. Exotic decays to a single photon and possible light mass "dark photon" (dark matter candidate) have been postulated with branching ratio up to O(10 −10 ) [53].…”

Parapositronium can decay into three photons

“…Similar to the π 0 → 3γ and o-Ps → γν ν decays, the diagrams that contribute to p-Ps → 3γ must contain an axial-vector interaction in the trace along the fermion line in order to break C-symmetry [4,8]. At the one-loop level, this restricts the relevant diagrams to those that do not contain virtual photons.…”