Impact of the quenching of gA on the sensitivity of 0νββ experiments

Abstract

Detection of the neutrinoless ββ (0νββ) decay is of high priority in the particle- and neutrino-physics communities. The detectability of this decay mode is strongly influenced by the value of the weak axial-vector coupling constant gA. The recent nuclear-model analyses of β and ββ decays suggest that the value of gA could be dramatically quenched, reaching ratios of gfree A /gA ≈ 4, where gfree A = 1.27 is the free, neutron-decay, value of gA. The effects of this quenching appear devastating for the sensitivity of the present and future 0νββ experiments since the fourth power of this ratio scales the 0νββ half-lives. This, in turn, could lead to some two orders of magnitude less sensitivity for the 0νββ experiments. In the present article it is shown that by using a consistent approach to both the two-neutrino ββ and 0νββ decays by the proton-neutron quasiparticle random-phase approximation, the feared two-orders-of-magnitude reduction in the sensitivity of the 0νββ experiments actually shrinks to a reduction by factors in the range 2–6. This certainly has dramatic consequences for the potential to detect the 0νββ decay.