Abstract
We used a high-resolution magnetic spectrograph to study neutron pair-correlated 0+ states in 136Ba, produced via the Ba138(p,t) reaction. In conjunction with state-of-the-art shell model calculations, these data benchmark part of the dominant Gamow-Teller component of the nuclear matrix element (NME) for 136Xe neutrinoless double beta (0νββ) decay. We demonstrate for the first time an evaluation of part of a 0νββ decay NME by use of an experimental observable, presenting a new avenue of approach for more accurate calculations of 0νββ decay matrix elements.
Highlights
We used a high-resolution magnetic spectrograph to study neutron pair-correlated 0+ states in 136Ba, produced via the 138Ba(p, t) reaction
We demonstrate for the first time an evaluation of part of a 0νββ decay nuclear matrix element (NME) by use of an experimental observable, presenting a new avenue of approach for more accurate calculations of 0νββ decay matrix elements
This is consistent with most theories beyond the standard model [5], that attribute the smallness of neutrino masses to a violation of total lepton number at an energy scale of ∼ 1015 GeV [3, 5]
Summary
2.35 in large uncertainties for the NMEs, which limit the physics that can be addressed, and the planning and execution of future 0νββ decay experiments [11]. While some of these results are in reasonable agreement with each other, there still exist large discrepancies in the calculated values, depending on the method used. Two methods that have been traditionally used to calculate 0νββ decay NMEs are the interacting shell model (ISM) and the quasiparticle random phase approximation (QRPA) Unlike the latter, the shell model calculations use a limited configuration space that is comprised of relatively fewer single-particle states in the vicinity of the Fermi surface. Compared to the spherical QRPA [21], the deformed calculations yield smaller values for the NME, and are in reasonable agreement with the ISM results. It has been suggested that these values are most likely overestimated, because of the omission of both collective as well as non-collective correlations, depending on the calculation [11, 28, 38, 39]
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