Muon Capture on 3He and the Weak Structure of the Nucleon

The weak form factors of the nucleon, including the induced pseudoscalar form factor and second class terms, are constrained using a microscopic calculation of the weak capture process ${}^{3}He({\mu }^{-},{\nu }_{\mu }{)}^{3}H$. The calculation is parameter free, and yields a rate of 1499(16) Hz, in agreement with the remarkable experimental measurement 1496(4) Hz. The nuclear wave functions are obtained using the EIHH method with the Argonne V18 nucleon–nucleon potential and the Urbana-IX three nucleon force. The weak currents in the nuclei are described using HB$\chi$PT formalism. The induced pseudoscalar form factor is found to agree with HB$\chi$PT prediction. The result is compatible with vanishing second class currents, with the tightest constraint to date on the conservation of vector current (CVC) hypothesis.