S. N. Gninenko, N. V. Krasnikov, V. A. Matveev
The invisible decay of muonium atom M->invisible, M=\mu+ e- bound state, is expected to be a very rare process which has never been experimentally tested. In the standard model it goes via the \mu+ e- annihilation into two neutrinos, with the branching fraction predicted to be Br(M -> \nu_\mu \nu_e) = 6.6 \times 10^{-12} with respect to the ordinary muon decay rate. Using the reported experimental results on searches for muonium-antimuonium conversion at PSI we set the first limit Br(M -> invisible) < 4.6 \times 10^{-3} (90% C.L.), while still leaving a big gap of about nine orders of magnitude between this bound and the predictions. To improve substantially the limit, we proposed to perform an experiment dedicated to the sensitive search for the M-> invisible decay. A feasibility study of the experimental setup shows that the sensitivity of the search for this decay mode in branching fraction Br(M -> invisible) at the level of 10^{-12} could be achieved. If the proposed search results in a substantially higher branching fraction than predicted, say Br(M -> invisible) ~ 10^{-10}, this would unambiguously indicate the presence of new physics. We point out that such a possibility may occur due the muonium transition into a hidden sector and consider, as an example, muonium-mirror muonium conversion in the mirror matter model. A result in agreement with the Standard Model prediction would provide a theoretically clean check of the pure leptonic bound state annihilation through the charged current weak interactions, and provide constraints for further attempts beyond the Standard Model. We believe our work provides strong motivations to perform the proposed experiment on search for the invisible decay of muonium in near future.
View original:
http://arxiv.org/abs/1209.0060
No comments:
Post a Comment