# An Improved Limit on Invisible Decays of Positronium

Abstract : 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 $(6.31\pm0.28) \times 10^6$ 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: $\binvdecay<4.2\times 10^{-7}$ (90% C.L.) Our results provide a limit on the photon mirror-photon mixing strength $\epsilon \leq 1.55\times 10^{-7}$ (90% C.L.) and rule out particles lighter than the electron mass with a fraction $Q_x \leq 3.4 \times 10^{-5}$ of the electron charge. Furthermore, upper limits on the branching ratios for the decay of parapositronium $Br(p-Ps\to invisible)\leq 4.3 \times 10^{-7}$ (90% C.L.) and the direct annihilation $Br(e^+e^-\to invisible)\leq 2.1 \times 10^{-8}$ (90% C.L.) could be set.
Document type :
Journal articles

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Submitted on : Thursday, November 16, 2006 - 5:45:16 PM
Last modification on : Friday, November 6, 2020 - 3:25:40 AM

### Citation

A. Badertscher, P. Crivelli, W. Fetscher, U. Gendotti, S. Gninenko, et al.. An Improved Limit on Invisible Decays of Positronium. Physical Review D, American Physical Society, 2007, 75, pp.032004. ⟨10.1103/PhysRevD.75.032004⟩. ⟨in2p3-00114512⟩

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