The results of a new search for positronium decays into invisible final states are reported. Convincing detection of this decay mode would be a strong evidence for new physics beyond the standard model (SM): for example, the existence of extra dimensions, of milli-charged particles, of new light gauge bosons or of mirror particles. Mirror matter could be a relevant dark matter candidate. In this paper the setup and the results of a new experiment are presented. In a collected sample of about (6.31±0.28)×106 orthopositronium decays, no evidence for invisible decays in an energy [0,80] keV was found and an upper limit on the branching ratio of orthopositronium o-Ps→invisible could be set: Br(o-Ps→invisible)<4.2×10-7(90%C.L.) Our results provide a limit on the photon mirror-photon mixing strength γ≤1.55×10-7(90%C.L.) and rule out particles lighter than the electron mass with a fraction Qx≤3.4×10-5 of the electron charge. Furthermore, upper limits on the branching ratios for the decay of parapositronium Br(p-Ps→invisible)≤4.3×10-7(90%C.L.) and the direct annihilation Br(e+e-→invisible)≤2.1×10-8(90%C.L.) could be set.
Physical Review D
- Pub Date:
- February 2007
- Electromagnetic processes and properties;
- Electromagnetic decays;
- High Energy Physics - Experiment
- 17 pages, 7 figures, added references, fixed limit on millicharged particles and changed two plots accordingly