Two-neutrino $\beta \beta$ decay of ${}^{136}$Xe to the first excited $0^{+}$ state in ${}^{136}$Ba

Lotta Jokiniemi, Beatriz Romeo, Catharina Brase +4

We calculate the nuclear matrix element for the two-neutrino $\beta \beta$ decay of ${}^{136}$Xe into the first excited $0^{+}$ state of ${}^{136}$Ba. We use different many-body methods: the quas…