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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.
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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

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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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