Nuclear muon capture (NMC) begins with a weak interaction process occurring within the nuclear volume. Information about NMC comes from the final-state particles, of which protons and deuterons are important components. However, published information is
rather limited despite being important for the design of some current searches for lepton flavor violation. $\mu^-$ Al data taken using the TWIST spectrometer, which was developed for a precise measurement of the Michel spectrum, were analyzed to obtain momentum spectra of protons and deuterons following NMC on aluminum.
Using a novel unfolding technique, a precision of better than 10% over the momentum range of 100–190 MeV/c for protons is obtained; for deuterons of 145–250 MeV/c the precision is better than 20%. Values for the measured partial and extrapolated total yields will be reported. A comparison is made with other measurements and model predictions.