## Abstract

In the last twenty years, the theory of hyperfine splitting in muonium developed without any experimental input. Finally, this situation is changing and a new experiment on measuring hyperfine splitting in muonium is now in progress at J-PARC. The goal of the MuSEUM experiment is to improve by an order of magnitude experimental accuracy of the hyperfine splitting and muon-electron mass ratio. Uncertainty of the theoretical prediction for hyperfine splitting will be crucial for comparison between the forthcoming experimental data and the theory in search of a possible new physics. In the current literature estimates of the error bars of the theoretical prediction differ roughly by a factor of two. We explain the origin of this discrepancy and obtain the theoretical prediction for the muonium hyperfine splitting Δν_{HFS} ^{th}(Mu)=4463302872(515)Hz,δ=1.2×10^{−7}.

Original language | English |
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Pages (from-to) | 113-116 |

Number of pages | 4 |

Journal | Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics |

Volume | 795 |

DOIs | |

State | Published - Aug 10 2019 |

### Bibliographical note

Funding Information:Of course, I am solely responsible for the contents of this paper. This work is supported by the NSF grant PHY-1724638 .

Funding Information:

I am deeply grateful to Barry Taylor for numerous very helpful and illuminating discussions. The original version of this paper contained an about 8 Hz inaccuracy in the estimate of the uncertainty in the first parentheses in Eq. (8). It arose due to an improper account for the reduced mass factor in the Fermi frequency in Eq. (6). I am thankful to Peter Mohr for discovering this mistake. Of course, I am solely responsible for the contents of this paper. This work is supported by the NSF grant PHY-1724638.

Publisher Copyright:

© 2019 The Author(s)

## ASJC Scopus subject areas

- Nuclear and High Energy Physics