Shell Model description of the ββ decay of 136Xe

We study in this Letter the double beta decay of Xe-136 with emission of two neutrinos which has been recently measured by the EXO-200 Collaboration. We use the same shell model framework, valence space, and effective interaction that we have already employed in our calculation of the nuclear matrix element (NME) of its neutrinoless double beta decay. Using the quenching factor of the Gamow-Teller operator which is needed to reproduce the very recent high resolution Xe-136 (He-3, t) Cs-136 data, we obtain a nuclear matrix element M-2 nu = 0.025 MeV-1 compared with the experimental value M-2 nu =0.019(2) MeV-1. (C) 2012 Elsevier B.V. All rights reserved.