2006/09/30 by A. Badertscher, P. Crivelli, W. Fetscher +6 · 2 citations
Physics and Astronomy · #hep-ex
paper · pdf · doi:10.1103/physrevd.75.032004
published as Phys.Rev.D75:032004,2007 · 17 pages, 7 figures, added references, fixed limit on millicharged particles and changed two plots accordingly
arxiv created 2006/10/05 · arxiv updated 2009/12/01
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 evid ence 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 decay s, no evidence for invisible decays in an energy window [0,80] keV was found and an upper limit on the branching ratio of orthopositronium \invdecay could be set: \binvdecay<4.2× 10-7 (90% C.L.) Our results provide a limit on the photon mirror-photon mixing strength ε≤ 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.