6533b820fe1ef96bd1279c29

RESEARCH PRODUCT

Consistent large-scale shell-model analysis of the two-neutrino ββ and single β branchings in 48Ca and 96Zr

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Abstract Two-neutrino double-beta-decay matrix elements M 2 ν and single beta-decay branching ratios were calculated for 48Ca and 96Zr in the interacting nuclear shell model using large single-particle valence spaces with well-tested two-body Hamiltonians. For 48Ca the matrix element M 2 ν = 0.0511 is obtained, which is 5.5% smaller than the previously reported value of 0.0539. For 96Zr this work reports the first large-scale shell-model calculation of the nuclear matrix element, yielding a value M 2 ν = 0.0747 with extreme single-state dominance. These matrix elements, combined with the available ββ-decay half-life data, yield effective values of the weak axial coupling which in turn are used to produce in a consistent way the β-decay branching ratios of ( 7.5 ± 2.8 ) % for 48Ca and ( 18.4 ± 0.09 ) % for 96Zr. These are larger than obtained in previous studies, implying that the detection of the β-decay branches could be possible in dedicated experiments sometime in the (near) future.