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 neutrinophysics 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 g free A /gA ≈ 4, where g free 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 4th 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 (pnQRPA), 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.PACS numbers: 21.60.Jz, 23.40.Hc, 27.50.+e, 27.60.+j Keywords: Detectability of the neutrinoless double beta decay, nuclear matrix elements, quenching of the axial-vector coupling strength, sensitivity of the double-beta experiments

Calculation of the neutrinoless double- β decay matrix element within the realistic shell model

“…For the sake of the completeness, we point out that our results of the J π decomposition are similar to those obtained in other SM calculations, as for example in Ref. [24,68,74,75] for 48 Ca, 76 Ge, 82 Se, 130 Te, and 136 Xe decays, respectively.…”

“…We recall that the per- turbative behavior of the single β-decay operator provides a difference between the M 2ν values calculated at second and third order in perturbation theory which does not exceed 10% [61]. Here, we observe a less satisfactory perturbative behavior for our calculation of M 0ν , the difference between second-and third-order results being about 15% and 30% for 76 Ge, 82 Se, and 130 Te, 136 Xe 0νββ decays, respectively. The calculation of M 0ν for 48 Ca 0νββ decay exhibits the worst perturbative behavior.…”

“…It is worth to observe that, from our results of the calculation of M 2ν s using both bare and effective single-β decay operators (see Tables II, IV, VI, and VIII in Ref. [48]), we may induce quenching factors of the axial coupling constant g A that are q = 0.83, 0.58, 0.56, 0.68, 0.61 for 48 Ca, 76 Ge, 82 Se, 130 Te, and 136 Xe decays, respectively.…”

“…Now, we consider the order-by-order convergence behavior by reporting in Figs. 5-9 the calculated values of M 0ν , M 0ν GT , and M 0ν F for 48 Ca, 76 Ge, 82 Se, 130 Te, and 136 Xe0νββ decay, respectively, from first-up to thirdorder in perturbation theory. We compare the order-byorder results also with their Padé approximant [2|1], as an indicator of the quality of the perturbative behavior [73].…”

“…In Section II details about the derivation of the effective SM Hamiltonian and 0νββ operator from a realistic V N N are reported. We show the results of calculations of M 0ν for 48 Ca, 76 Ge, 82 Se, 130 Te, and 136 Xe double-β decay in Section III, and present also a detailed study of the perturbative properties of O 0ν eff , together with an analysis of the angular momentum-parity matrix-element distributions and a comparison with recent SM results. The conclusions of this study are drawn in Section IV, together with the perspectives of our current project.…”