Researchers define the parameter spaces where future tests could detect—or rule out—a novel interaction by researching physics models outside the standard model.
An antimuon and an electron are bonded together in a hydrogen-like state to form the unusual element muonium. The interaction between muonium and antimuonium, which consists of a muon and a positron, would contradict the conservation of lepton flavor number in the standard model of particle physics. Detecting a muonium-to-antimuonium transition, for example, would be an unambiguous indicator of physics beyond the standard model. Takeshi Fukuyama of Osaka University and colleagues have analyzed numerous models of beyond-standard-model physics and investigated the predictions they make regarding the muonium-to-antimuonium transition in light of recent experimental data . Their findings should help researchers analyze upcoming tests in Japan and China to look for signals of this change in the near future.
The latest direct studies on the muonium-to-antimuonium transition took place in the late 1990s. In the twenty-or-so years since, however, experiments have yielded results that indirectly relate to this transition, such as measurements of neutrino-oscillation parameters and constraints on new particles predicted by the same lepton-flavor-number-violating models that predict the muonium-to-antimuonium transition. Fukuyama and colleagues analyzed numerous theories of physics beyond the standard model based on these recent experimental discoveries and calculated the parameter spaces where future studies may detect—or rule out—the transition for a specific paradigm. The Zee-Babu model, for example, was shown to have the highest likelihood of a muonium-to-antimuonium transition happening among a class of models known as radiative neutrino mass models. Experiments to look for the transition are planned at the Japan Proton Accelerator Research Complex and the China Spallation Neutron Source, and these models might be put to the test.
1. T. Fukuyama et al., “Models of the muonium to antimuonium transition,” Phys. Rev. D 105, 015026 (2022).