Benchmarking ${}^{136}$Xe Neutrinoless $\beta \beta$ Decay Matrix Element Calculations with the ${}^{138}\mathrm{Ba}(p,t)$ Reaction

Abstract

We used a high-resolution magnetic spectrograph to study neutron pair-correlated $0^{+}$ states in ${}^{136}$Ba, produced via the ${}^{138}\mathrm{Ba}(p,t)$ reaction. In conjunction with state-of-the-art shell model calculations, these data benchmark part of the dominant Gamow-Teller component of the nuclear matrix element (NME) for ${}^{136}$Xe neutrinoless double beta ($0\nu \beta \beta$) decay. We demonstrate for the first time an evaluation of part of a $0\nu \beta \beta$ decay NME by use of an experimental observable, presenting a new avenue of approach for more accurate calculations of $0\nu \beta \beta$ decay matrix elements.