Two-neutrino Decay of Xe to the first excited 0 State in Ba
L. Jokiniemi (TRIUMF, Vancouver, Canada)
; B. Romeo (Donostia International Physics Center, San Sebastián, Spain); C. Brase (Max-Planck-Institut für Kernphysik, Heidelberg, Germany, ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany, Technische Universität Darmstadt, Department of Physics, Darmstadt, Germany); J. Kotila (Department of Physics, University of Jyväskylä, Jyväskylä, Finland, Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, USA, Finnish Institute for Educational Research, University of Jyväskylä, Jyväskylä, Finland); P. Soriano (Departament de Física Quàntica i Astrofísica, Universitat de Barcelona, Barcelona, Spain, Institut de Ciències del Cosmos, Universitat de Barcelona, Barcelona, Spain); et al - Show all 7 authors
We calculate the nuclear matrix element for the two-neutrino ββ decay of $^{136}$Xe into the first excited state of $^{136}$Ba. We use different many-body methods: the quasiparticle random-phase approximation (QRPA) framework, the nuclear shell model, the interacting boson model (IBM-2), and an effective field theory (EFT) for β and ββ decays. While the QRPA suggests a decay rate at the edge of current experimental limits, the shell model points to a half-life about two orders of magnitude longer. The predictions of the IBM-2 and the EFT lie in between, and the latter provides systematic uncertainties at leading order. An analysis of the running sum of the nuclear matrix element indicates that subtle cancellations between the contributions of intermediate states can explain the different theoretical predictions. For the EFT, we also present results for two-neutrino ββ decays to the first excited state in other nuclei.
