Aspects of pion and muon capture

This dissertation reviews particle, nuclear, and atomic physics aspects of negative pion and muon capture, as illustrated by experiment. Atomic-capture of negative pions was studied in an high precision pionic x-ray measurement. The charged-pion mass was determined to seven parts-per-million uncertainty; and the pionic x-ray fine-structure predicted by the Klein-Gordan equation was observed. This experiment also established an upper limit on the muon neutrino mass of 570 keV at the 90% confidence level. Particle-physics aspects have been investigated in the pion-like process of nuclear muon capture on the deuteron. By selecting back-to-back neutron events where little momentum is carried by the muon neutrino, it was possible to observe the enhancement to the neutron energy spectrum predicted by meson-exchange current corrections to the muon capture-reaction calculations. Nuclear reactions following stopped negative pion capture in 165Ho and 181Ta have been investigated by coincidence measurements of gamma rays and neutrons emitted by the reaction products. The observed neutron spectra are compared to spectra calculated by a hybrid exciton model calculation of pre-equilibrium neutron emission. The model was modified to include the kinematics of pion capture on a pair of correlated nucleons