Abstract
High precision measurements of the ground state hyperfine structure (HFS) of muonium is a stringent tool for testing bound-state quantum electrodynamics (QED) theory, determining fundamental constants of the muon magnetic moment and mass, and searches for new physics. Muonium is the most suitable system to test QED because both theoretical and experimental values can be precisely determined. Previous measurements were performed decades ago at LAMPF with uncertainties mostly dominated by statistical errors. At the J-PARC Muon Science Facility (MUSE), the MuSEUM collaboration is planning complementary measurements of muonium HFS both at zero and high magnetic field. The new high-intensity muon beam that will soon be available at H-Line will provide an opportunity to improve the precision of these measurements by one order of magnitude. An overview of the different aspects of these new muonium HFS measurements, the current status of the preparation for high-field measurements, and the latest results at zero field are presented.
Highlights
Muonium is a hydrogen-like atom made of a bound state of a positive muon and an electron
The hyperfine structure of positronium, which is a bound state of a positron and an electron, is limited experimentally by its mean lifetime (i.e. 140 ns for ortho-positronium) and measured with an accuracy of only 3.3 ppm [3,4,5], while its theoretical value is calculated at a level of 1.1 ppm [6] with uncertainties from unknown nonlogarithmic higher-order terms
The previous muonium hyperfine structure (HFS) measurement at zero field [7] reached a precision of 310 ppb, while the one at high field [8] achieved 12 ppb, both performed at LAMPF and with experimental uncertainties mostly dominated by statistical errors
Summary
Muonium is a hydrogen-like atom made of a bound state of a positive muon and an electron. High precision measurements of the muonium ground state hyperfine structure (HFS) can be regarded as the most sensitive tool for testing quantum electrodynamics (QED), and for determining precisely fundamental constants of the muon magnetic moment and its mass. The previous muonium HFS measurement at zero field [7] reached a precision of 310 ppb, while the one at high field [8] achieved 12 ppb, both performed at LAMPF and with experimental uncertainties mostly dominated by statistical errors. In addition to test QED, it should be noted that the experimental values of the muon magnetic moment and mass are still currently determined by the previous muonium HFS experiment at high field [8]. An overview of the different aspects of these new precise muonium HFS measurements, the current status of the preparation for high-field measurements, and the latest measurements at zero field are presented
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