Muon Capture on the Proton and Deuteron

TL;DR

The paper discusses measurements of muon capture on protons and deuterons to determine fundamental couplings and test QCD predictions, with implications for astrophysical processes.

Contribution

It reports on the MuCap experiment's measurement of muon capture on the proton and introduces the MuSun experiment for deuteron capture, advancing understanding of weak interactions in nucleons.

Findings

15% precision in g_p measurement from MuCap

MuSun experiment in final design stage

Connections to astrophysical reactions via effective field theories

Abstract

By measuring the lifetime of the negative muon in pure protium (hydrogen-1), the MuCap experiment determines the rate of muon capture on the proton, from which the proton's pseudoscalar coupling g_p may be inferred. A precision of 15% for g_p 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.