Muonium hyperfine structure and hadronic effects

Abstract

A new result for the hadronic vacuum polarization correction to the muonium hyperfine splitting (HFS) is presented: $\Delta \nu \left(\mathrm{had}\mathrm{-}\mathrm{vp}\right)=(0.233\mathrm{}\pm 0.003)\mathrm{kHz}.$ Compared with previous calculations, the accuracy is improved by using the latest data on $e^{+}{e}^{-}\to$ hadrons. The status of the QED prediction for HFS is discussed.