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Register a new userNew Bounds from Searching for Muonium to Antimuonium Conversion
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L.Willmann
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A new upper limit for the probability of spontaneous muonium to antimuonium conversion was established at ${rm P_{Mbar{M}}} leq 8.2 cdot 10^{-11}$ (90%C.L.) in 0.1~T magnetic field, which implies consequences for speculative extensions to the standard model. Coupling parameters in R-parity violating supersymmetry and the mass of a flavour diagonal bileptonic gauge boson can be significantly restricted. A Z$_8$ model with radiative mass generation through heavy lepton seed and the minimal version of 331-GUT models are ruled out.
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A new result from searching for muonium to antimuonium conversion is reported which sets an upper limit on the coupling constant in an assumed $(V-A) times (V-A)$ type interaction of $G_{Mbar{M}} leq 3cdot 10^{-3} G_F$ ~ (90% C.L.). A particular Z_8 and a minimal 331 GUT model can be ruled out. Further new and stringent limits can be set for masses of bileptonic gauge bosons and $lambda$ parameters in R-parity breaking supersymmetric models.
A new experimental search for muonium-antimuonium conversion was conducted at the Paul Scherrer Institute, Villigen, Switzerland. The preliminary analysis yielded one event fulfilling all required criteria at an expected background of 1.7(2) events due to accidental coincidences. An upper limit for the conversion probability in 0.1 T magnetic field is extracted as $8 cdot 10^{-11}$ (90% CL).
A new experiment has been set up at the Paul Scherrer Institut to search for muonium to antimuonium conversion. No event was found to fulfil the requested signature which consists of the coincident detection of both constituents of the antiatom in its decay. Assuming an effective (V-A)$times$(V-A) type interaction an improved upper limit is established for the conversion probability of ${rm P_{Mbar{M}}} leq 8 cdot 10^{-9}$ (90%C.L.), which is almost two orders of magnitude lower compared to previous results and provides a sensitive test for theoretical extensions of the standard model.
The spontaneous muonium-to-antimuonium conversion is one of the interesting charged lepton flavor violation processes. MACE is the next generation experiment to probe such a phenomenon. In models with a triplet Higgs to generate neutrino masses, such as Type-II seesaw and its variant, this process can be induced by the doubly-charged Higgs contained in it. In this article, we study the prospect of MACE to probe these models via the muonium-to-antimuonium transitions. After considering the limits from $mu^+ rightarrow e^+ gamma $ and $mu^+ rightarrow e^+ e^- e^+$, we find that MACE could probe a parameter space for the doubly-charged Higgs which is beyond the reach of LHC and other flavor experiments.
The electron and muon number violating muonium-antimuonium oscillation process in an extended Minimal Supersymmetric Standard Model is investigated. The Minimal Supersymmetric Standard Model is modified by the inclusion of three right-handed neutrino superfields. While the model allows the neutrino mass terms to mix among the different generations, the sneutrino and slepton mass terms have only intra-generation lepton number violation but not inter-generation lepton number mixing. So doing, the muonium-antimuonium conversion can then be used to constrain those model parameters which avoid further constraint from the $muto egamma$ decay bounds. For a wide range of parameter values, the contributions to the muonium-antimuonium oscillation time scale are at least two orders of magnitude below the sensivity of current experiments. However, if the ratio of the two Higgs field VEVs, $tanbeta$, is very small, there is a limited possibility that the contributions are large enough for the present experimental limit to provide an inequality relating $tanbeta$ with the light neutrino mass scale $m_ u$ which is generated by see-saw mechanism. The resultant lower bound on $tanbeta$ as a function of $m_ u$ is more stringent than the analogous bounds arising from the muon and electron anomalous magnetic moments as computed using this model.
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