No abstract

Background: Direct determination of the neutrino mass through double-β decay is at the present time one of the most important areas of experimental and theoretical research in nuclear and particle physics. Purpose: We calculate nuclear matrix elements for the extraction of the average neutrino mass in neutrinoless double-β decay. Methods: The microscopic interacting boson model (IBM-2)

We introduce a method for isospin restoration in the calculation of nuclear matrix elements (NME) for 0νββ and 2νββ decay within the framework of IBM-2. With this method, we calculate NME for all processes of interest in 0νβ − β − , 2νβ − β − , and in 0νβ+ EC, and 2νECEC. With this method, the Fermi (F) matrix elements for 2νββ vanish, and those for 0νββ are considerably reduced.

Neutrinoless double-β decay is of fundamental importance for the determining neutrino mass.By combining a calculation of nuclear matrix elements within the framework of the microscopic interacting boson model (IBM-2) with an improved calculation of phase space factors, we set limits on the average light neutrino mass and on the average inverse heavy neutrino mass (flavor violating parameter).