Muon capture on the proton and deuteron

Abstract

By measuring the lifetime of the negative muon in pure protium ( 1 H), the MuCap experiment determines the rate of muon capture on the proton, from which the proton's pseudoscalar coupling gp may be inferred. A precision of 15% for gp has been published; this is a step along the way to a goal of 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD's chiral symmetry. Meanwhile, the MuSun experiment is in its final design stage; it will measure the rate of muon capture on the deuteron using a similar technique. This process can be related through pionless effective field theory and chiral perturbation theory to other two-nucleon reactions of astrophysical interest, including proton-proton fusion and deuteron breakup. Muon capture on the proton: theoretical motivationMuon capture arises from the interaction between a leptonic current (representing the muon's transformation into its neutrino) and a hadronic current (the proton's transformation into a neutron). The hadronic current may be parameterized by writing down terms with all possible a