Muon Capture in Hydrogen

An experiment to measure the muon capture rate in liquid hydrogen was carried out using scintillation counter techniques. The experiment tests muon-electron universality in the weak interaction with a proton at a momentum transfer of 100 MeV/c. The use of ultrapure liquid hydrogen, a purified muon beam, and neutron-gamma ray discriminating detectors made possible the detection of the 5.2-MeV neutron from the relatively improbable capture reaction (${\mu }^{-}+p\to n+\nu$). Observation of the well-known pion capture reaction (${\pi }^{-}+p\to n+\gamma$) served as a check on many aspects of the experimental arrangement as well as on the neutron detector efficiency calculation. Several internal checks confirm that impurity captures were negligible. The muon capture rate in the ${\left(p\mu p\right)}^{+}$ ortho molecular state was obtained. The muon molecular formation rate was measured in an independent experiment, but the present result is relatively insensitive to it. The stability of the ortho state against transition to the para ground state for times comparable to the free muon lifetime is confirmed. The experimental result of 464±42 ${\sec }^{-1\mathrm{}}$ is to be compared with 562 ${\sec }^{-1\mathrm{}}$, the rate expected on the basis of muon-electron universality, the conserved vector current theory, the calculated value of the induced pseudoscalar coupling, and the axial vector and vector coupling constants as determined in the $\beta$-decay interaction.