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Register a new userPrecision electroweak shift of muonium hyperfine splitting
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Electroweak second order shifts of muonium ($mu^+e^-$ bound state) energy levels are calculated for the first time. Calculation starts from on-shell one-loop elastic $mu^+ e^-$ scattering amplitudes in the center of mass frame, proceed to renormalization and to derivation of muonium matrix elements by using the momentum space wave functions. This is a reliable method unlike the unjustified four-Fermi approximation in the literature. Corrections of order $alpha G_F$ (with $alpha sim 1/137$ the fine structure constant and $G_F$ the Fermi constant) and of order $alpha G_F /(m_Z a_B)$ (with $m_Z$ the Z boson mass and $a_B$ the Bohr radius) are derived from three classes of Feynman diagrams, Z self-energy, vertex and box diagrams. The ground state muonium hyperfine splitting is given in terms of the only experimentally unknown parameter, the smallest neutrino mass. It is however found that the neutrino mass dependence is very weak, making its detection difficult.
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We report a new measurement of the $n=2$ Lamb shift in Muonium using microwave spectroscopy. Our result of $1047.2(2.3)_textrm{stat}(1.1)_textrm{syst}$ MHz comprises an order of magnitude improvement upon the previous best measurement. This value matches the theoretical calculation within one standard deviation allowing us to set limits on CPT violation in the muonic sector, as well as on new physics coupled to muons and electrons which could provide an explanation of the muon $g-2$ anomaly.
We evaluate the two-photon exchange corrections to the Lamb shift and hyperfine splitting of S states in electronic hydrogen relying on modern experimental data and present the two-photon exchange on a neutron inside the electronic and muonic atoms. These results are relevant for the precise extraction of the isotope shift as well as in the analysis of the ground state hyperfine splitting in usual and muonic hydrogen.
We constrain the possibility of a new pseudoscalar coupling between the muon and proton using a recent measurement of the 2S hyperfine splitting in muonic hydrogen.
The muonium atom is the purely leptonic bound state of a positive muon and an electron. It has a lifetime of 2.2 $mu$s. The absence of any known internal structure provides for precision experiments to test fundamental physics theories and to determine accurate values of fundamental constants. In particular groun dstate hyperfine structure transitions can be measured by microwave spectroscopy to deliver the muon magnetic moment. The frequency of the 1s-2s transition in the hydrogen-like atom can be determined with laser spectroscopy to obtain the muon mass. With such measurements fundamental physical interactions, in particular Quantum Electrodynamics, can also be tested at highest precision. The results are important input parameters for experiments on the muon magnetic anomaly. The simplicity of the atom enables further precise experiments, such as a search for muonium-antimuonium conversion for testing charged lepton number conservation and searches for possible antigravity of muons and dark matter.
We revisit the global fit to electroweak precision observables in the Standard Model and present model-independent bounds on several general new physics scenarios. We present a projection of the fit based on the expected experimental improvements at future $e^+ e^-$ colliders, and compare the constraining power of some of the different experiments that have been proposed. All results have been obtained with the HEPfit code.
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