The (3He,t) reaction on 76Ge, and the double-β-decay matrix element

A 76Ge(3He,t)76As charge-exchange experiment at an incident energy of 420 MeV has been performed with an energy resolution of 30 keV. The Gamow-Teller GT− strength distribution in 76As, which is the intermediate nucleus in the double-beta (ββ) decay of 76Ge, has been extracted. An unusually strong fragmentation of the GT− strength is observed even at low excitation energies of Ex⩽5MeV. By combining the data with those for GT+ transitions from a recent 76Se(d,2He)76As measurement, the nuclear matrix element for the 76Ge 2νββ decay has been evaluated. A lack of correlation among the GT transition strengths feeding the same levels from the two different directions is observed. The impact on the 76Ge 2νββ decay nuclear matrix element is discussed.