The ^{150}Nd(^{3}He,t) and ^{150}Sm(t,^{3}He) reactions with applications to ββ decay of ^{150}Nd

The 150 Nd( 3 He, t ) reaction at 140 MeV/u and 150 Sm( t , 3 He) reaction at 115 MeV/u were measured, populating excited states in 150 Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) ββ decay of 150 Nd to 150 Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless ββ decay (0 νββ ) of 150 Nd. The present results thus provide useful information on the neutrino responses for evaluating the 0 νββ and 2 νββ matrix elements. The 2 νββ matrix element calculated from the Gamow-Teller transitions through the lowest 1 + state in the intermediate nucleus is maximally about half of that deduced from the half-life measured in 2 νββ direct counting experiments and at least several transitions through 1 + intermediate states in 150 Pm are required to explain the 2 νββ half-life. Because Gamow-Teller transitions in the 150 Sm( t , 3 He) experiment are strongly Pauli-blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the 2 ~ ω , ∆ L = 0, ∆ S = 1 isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.