An update of muon capture on hydrogen

Understand

The successful precision measurement of the rate of muon capture on a proton by the MuCap Collaboration allows for a stringent test of the current theoretical understanding of this process.

• Chiral perturbation theory, which is a low-energy effective field theory that preserves the symmetries and the pattern of symmetry breaking in the underlying theory of QCD, offers a systematic framework for describing $\mu p$ capture and provides a basic test of QCD at the hadronic level.
• We describe how this effective theory with no free parameters reproduces the measured capture rate.
• A recent study has addressed new sources of uncertainties that were not considered in the previous works, and we review to what extent these uncertainties are now under control.