Nuclear structure calculation of? + ? +,? +/EC and EC/EC decay matrix elements

Abstract

Abstract. Nuclear matrix elements for double positron emisson ~+/?+), positron emission/electron capture (/?+/ EC) and double electron capture (EC/EC) in the 2v/?/? decay mode and for fl+/~+ and/~+/EC decay in the 0 v/?/~ mode are calculated for the experimentally most promising isotopes 58Ni, 78Kr, 96Ru, l~ 124Xe, 13~ and 136Ce within pn-QRPA. We point out that the matrix element for the 2vfl+/EC decay differs from the 2vfl+fl + matrix element, an effect not considered previously. For the neutrino accompanied decays our calculation predicts for the fl+/EC and the EC/EC mode half lives which are shorter typically by 4-7 orders of magnitude than those for the double positron emission. However, even for the best candidates typical values for 2vfi+/EC (2vEC/EC) are still in the range of ~ 1022 ((some) 1021) years. For 0 v/~/~ decay we have calculated all matrix elements relevant for both, the mass mechanism and the right-handed currents for the first time complete. A detailed discussion of the differences between the 0v/~+/q +, the Ovfl+/EC and Ovfi-fl decay is given.

Realistic shell-model calculations of the 2νββ nuclear matrix elements and the role of the shell structure in intermediate states

“…As a result, half-lives of T 2ν 1/2 (EC/EC; 36 Ar → 36 S) = 1.7 × 10 29 yr, T 2ν 1/2 (EC/EC; 54 Fe → 54 Cr) = 1.5 × 10 27 yr are obtained from the present nuclear matrix-elements. The half-lives of the 58 Ni decay is shown in Table 1, in comparison with the QRPA results [6] and the data [23]. The present calculation gives half-lives somewhat longer, but comparable to those by the QRPA calculation.…”

“…Since the electron capture (EC) and positron emission (β + ) are possible in a single-GT + transition, we have three cases in the double-GT + transitions; EC/EC, β + /EC and β + β + [4,5]. It has been pointed out that, in the 0ν mode, they seem to yield quite a different constraint on the neutrino masses and right-handed weak-current parameters [6], although the double-GT + transitions are more difficult to be observed than the β − β − cases. From the viewpoint of the nuclear structure theories, there is no essential distinction in the algorithm to compute the ββ matrix-elements, between the β − and the β + cases.…”

Neutrinoless double-beta decay and physics beyond the standard model

“…More directly, it is also possible to infer the dominant mechanism purely within the context of neutrinoless double beta decay and closely related processes. Relevant techniques discussed in the literature include (i) the comparison of 0νββ decay rates in different isotopes [104][105][106] (this possibility is discussed in detail in the contribution by Fogli et al), (ii) the comparison of 0νβ − β − with 0νβ + β + [107], (iii) the comparison of 0νββ with electron capture [107], (iv) the comparison of of 0νββ decay to the ground state and an excited state [108] and (v) the experimental determination of the angular and energy distribution of the outgoing electrons in 0νββ [4,[109][110][111][112][113][114].…”

Analysis of mechanisms that could contribute to neutrinoless double-beta decay

“…Refs. [40][41][42][43][44] among other). Our analysis is however more detailed and more specific to the decay of the 82 Se isotope.…”