A study of weak nuclear response by nuclear muon capture

Abstract

Nuclear matrix elements (NMEs) for double beta decays (DBD) are crucial for extracting fundamental neutrino properties from DBD experiments. In order to study the DBD NMEs, single B+ and B- NMEs are required. The present research developed an experimental approach towards the determination of weak nuclear response (square of the NME) for the importance of fundamental properties of neutrinos. Hence, the present research aims at experimental studies of muon capture strength distributions, the B+ side responses, to help/confirm theoretical evaluation for DBD NMEs. Nuclear muon capture induced the excitation of the nucleus by compound nuclear formation and de-excitation of the compound nucleus by neutron emission. However, captures on the excited states of nucleus are preferable in comparison with capture on the ground state. The gamma rays accompanied the neutron emission is from the transitions from an excited state to the ground state. The production of isotope after muon capture evaluated the capture strength via observation of nuclear gamma rays and X-rays. We used the enriched molybdenum thin film in our frst measurement at J-PARC, MLF. The statistical neutron decay calculator explained the theoretical approach with the limitation to the excitation energy which corresponds to the Q-value of muon captures. Neutron binding energy is the threshold energy for emission of neutron and their cascade process after nuclear excitation is explained by emission of the fast pre-equilibrium neutrons(PEQ) and evaporating neutrons(EQ) fraction. The second part discusses the experimental observation of isotope production after (p,xn) reaction on 100Mo target with x = 0,1,2, ... neutron emission. The isotopes are identified by their gamma-rays following the capture reaction and the observed half-life from the decay curve. The final phase elaborates the comparison of previous feasibility test on NatMo and the current 100Mo experimental observations with the neutron statistical calculations for both natural and enriched Molybdenum targets. From the population of isotopes produced by the reaction, one may get the muon-capture strength distribution, which can be used to help deduce the nuclear responses relevant to neutrino less double beta decays.