title: Large-Scale Shell-Model Analysis of the Neutrinoless ββ Decay of ^{48}Ca.
abstract: We present the nuclear matrix element for the neutrinoless double-beta decay of ^{48}Ca based on large-scale shell-model calculations including two harmonic oscillator shells (sd and pf shells). The excitation spectra of ^{48}Ca and ^{48}Ti, and the two-neutrino double-beta decay of ^{48}Ca are reproduced in good agreement to the experimental data. We find that the neutrinoless double-beta decay nuclear matrix element is enhanced by about 30% compared to pf-shell calculations. This reduces the decay lifetime by almost a factor of 2. The matrix-element increase is mostly due to pairing correlations associated with cross-shell sd-pf excitations. We also investigate possible implications for heavier neutrinoless double-beta decay candidates.
authors.affiliation: Center for Nuclear Study, The University of Tokyo, 113-0033 Tokyo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Iwata
authors.affiliation: Center for Nuclear Study, The University of Tokyo, 113-0033 Tokyo, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Shimizu
authors.affiliation: Center for Nuclear Study, The University of Tokyo, 113-0033 Tokyo, Japan.|Department of Physics, The University of Tokyo, 113-0033 Tokyo, Japan.|National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium.
authors.forename: T
authors.initials: T
authors.lastname: Otsuka
authors.affiliation: Center for Nuclear Study, The University of Tokyo, 113-0033 Tokyo, Japan.|Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, 319-1195 Ibaraki, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Utsuno
authors.affiliation: Department of Physics, The University of Tokyo, 113-0033 Tokyo, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Menéndez
authors.affiliation: Center for Mathematical Sciences, University of Aizu, 965-8580 Fukushima, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Honma
authors.affiliation: Department of Physics, The University of Tokyo, 113-0033 Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Abe