Majorana parameters of the interacting boson model of nuclear structure and their implication for 0νββ decay

Abstract

The well-known spherical-deformed-transitional nucleus and potential $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}\phantom{\rule{4pt}{0ex}}$emitter $^{150}\mathrm{Nd}\phantom{\rule{4pt}{0ex}}$and its daughter $^{150}\mathrm{Sm}\phantom{\rule{4pt}{0ex}}$were investigated in nuclear resonance fluorescence experiments using quasimonoenergetic, linearly polarized $\ensuremath{\gamma}$-ray beams. For both nuclei transitions from the ${1}^{+}$ scissors mode to the ${0}_{2}^{+}$ and ${2}_{2}^{+}$ states were observed for the first time and their respective $M1$ transition strengths were determined. Through a systematic investigation, a sensitivity of these transition strengths to the three Majorana parameters of the interacting boson model-2 (IBM-2) was established. In combination with the novel experimental data, this poses strong constraints to the Majorana parameters in improved IBM-2 representations of both nuclei. A subsequent recalculation of the nuclear matrix elements (NMEs) for the $^{150}\mathrm{Nd}\ensuremath{\rightarrow}^{150}\mathrm{Sm} 0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}\phantom{\rule{4pt}{0ex}}$decay in the IBM-2 with these improved representations results in ${M}_{\text{IBM-2}}^{(0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta})}[{0}_{1}^{+}]=3.35$ for the NME for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}\phantom{\rule{4pt}{0ex}}$decay into the ground state of $^{150}\mathrm{Sm}\phantom{\rule{4pt}{0ex}}$and ${M}_{\text{IBM-2}}^{(0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta})}[{0}_{2}^{+}]=1.30$ for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}\phantom{\rule{4pt}{0ex}}$decay to its ${0}_{2}^{+}$ state.