Neutrinoless double-electron capture

Abstract

Direct determination of the neutrino mass is at the present time one of the most important aims of experimental and theoretical research in nuclear and particle physics. A possible way of detection is through neutrinoless double-electron capture, $0\ensuremath{\nu}\mathrm{ECEC}$. This process can only occur when the energy of the initial state matches precisely that of the final state. We present here a calculation of prefactors (PFs) and nuclear matrix elements (NMEs) within the framework of the microscopic interacting boson model (IBM-2) for $^{124}\mathrm{Xe}$, $^{152}\mathrm{Gd}$, $^{156}\mathrm{Dy}$, $^{164}\mathrm{Er}$, and $^{180}\mathrm{W}$. From the PF and NME we calculate the expected half-lives and obtain results that are of the same order as those of $0\ensuremath{\nu}{\ensuremath{\beta}}^{+}{\ensuremath{\beta}}^{+}$ decay, but considerably longer than those of $0\ensuremath{\nu}{\ensuremath{\beta}}^{\ensuremath{-}}{\ensuremath{\beta}}^{\ensuremath{-}}$ decay.