Shell model study of Ca40 muon capture and the (0+,0keV)→(0-,2626 keV) axial charge transition

We report results from shell-model studies of muon capture on Ca40 to low-lying levels of K40. We discuss the comparison among calculated capture rates, measured capture rates, and analogous transitions in (e,e') scattering in terms of the particle-hole structure of the Ca40-K40 nuclei. We highlight the Ca40(0+,0)→K40(0-,2626) axial charge transition and its sensitivity to the induced pseudoscalar coupling gp of the proton's weak interaction. In addition, we address the hindrance of unique first-forbidden transitions due to particle-hole interactions and the emergence of allowed Gamow-Teller transitions due to ground-state correlations. Last, we examine the longitudinal alignment of K40 recoils following muon capture and discuss this possibility for independently determining the induced coupling gp.