Nuclear matrix elements for0νββdecays with light or heavy Majorana-neutrino exchange

Abstract

We compute the nuclear matrix elements (NMEs) corresponding to the neutrinoless double beta (OvfiP) decays of nuclei which attract current experimental interest. We concentrate on ground-state-to-ground-state decay transitions mediated by light (1-NMEs) or heavy (h-NMEs) Majorana neutrinos. The computations are done in realistic single-particle model spaces using the proton-neutron quasiparticle random-phase approximation (pnQRPA) with two-nucleon interactions based on the Bonn one-boson-exchange G matrix. Both the 1-NMEs and the h-NMEs include the appropriate short-range correlations, nucleon form factors, and higher-order nucleonic weak currents. In addition, both types of NMEs are corrected for the isospin symmetry by the recently proposed method in which the particle-particle proton-neutron interaction parameter (gpp) is decomposed into isoscalar (£pp=°) and isovector ( g^1) parts. A detailed analysis of the 1-NMEs and the h-NMEs is performed to benchmark our computer code and to compare with other recent calculations which produce h-NMEs that are in tension with each other.

Neutrinoless double beta decay in chiral effective field theory: lepton number violation at dimension seven

“…Here we follow refs. [67,73,74,76] and separate the direct axial, induced pseudoscalar, and magnetic contributions. We then have the following expressions for h F , h GT , and…”

“…those of ref. [76], and define the following neutrino potentials 7 Having defined the neutrino potentials, we express the nuclear matrix elements (NMEs) as…”

“…The observation of 0νββ would have far reaching implications: it would demonstrate that neutrinos are Majorana fermions [2], shed light on the mechanism of neutrino mass generation, and give insight on leptogenesis scenarios for the generation of the matterantimatter asymmetry in the universe [3]. The current experimental limits on the halflives are already impressive [4][5][6][7][8][9][10][11][12][13], at the level of T 0ν 1/2 > 5.3 × 10 25 y for 76 Ge [12] and T 0ν 1/2 > 1.07 × 10 26 y for 136 Xe [13], with next generation ton-scale experiments aiming at a sensitivity of T 0ν 1/2 ∼ 10 27−28 y. By itself, the observation of 0νββ would not immediately point to the underlying physical origin of LNV.…”

Search for Neutrinoless Double-Beta Decay ofTe130with CUORE-0

“…[32], the most recent nuclear matrix element (NME) calculations for a broad range of models [33][34][35][36][37], and assuming g A ≃ 1.27 for the axial coupling constant. The resulting range for the 90% C.L.…”

Global constraints on absolute neutrino masses and their ordering

“…A worldwide search is underway to find possible 0νββ decay signatures in a variety of nuclei, and lower limits on the corresponding half lives have been placed [53][54][55]. Transforming lower bounds on T into upper bounds on m ββ requires theoretical input on the NME and their uncertainties [15,[50][51][52][56][57][58]. The strongest m ββ limit to date is provided by the KamLAND-Zen experiment with 136 Xe, that finds T > 1.07 × 10 26 yr (90% C.L.…”