Ordinary Muon Capture on 136Ba: Comparative Study Using the Shell Model and pnQRPA

In this work, we present a study of ordinary muon capture (OMC) on 136Ba, the daughter nucleus of the 136Xe double beta decay (DBD). OMC rates to low-lying nuclear states (below 1 MeV of excitation energy) in 136Cs are assessed by using both the interacting shell model (ISM) and the proton-neutron quasiparticle random-phase approximation (pnQRPA). We also add the chiral two-body (2BC) meson-exchange currents and use an exact Dirac wave function for the captured s-orbital muon. OMC can be viewed as a complementary probe of the wave functions in 136Cs, the intermediate nucleus of the 136Xe DBD. At the same time OMC can be considered as a powerful probe of the effective values of the weak axial-type couplings in a 100-MeV momentum-exchange region relevant for the neutrinoless DBD. The present work represents the first attempt to compare the ISM and pnQRPA results for the OMC on a heavy nucleus by including also the exact muon wave function and the 2BC. Sensitivity estimates of the present and future neutrinoless DBD experiments will clearly benefit from the future OMC measurements through the OMC calculations similar to the present one.