Sensitivity of nuclear matrix elements of 0νββ of Ca48 to different components of the two-nucleon interaction

Abstract

In the present work, we examine the sensitivity of nuclear matrix elements (NMEs) for light neutrino-exchange mechanism of neutrinoless double beta decay (0νββ) of 48Ca to the central, spin-orbit, and tensor components of two-nucleon interaction. The NMEs are calculated in the nuclear shell-model framework in f p-model space using frequently used GXPF1A interaction and a new effective interaction named GX1R of pf shell. The decomposition of the shell-model two-nucleon interactions into their individual components is performed using spin-tensor decomposition. The NMEs are calculated in closure approximation by using optimal value of the closure energy. The results shows that the total NMEs calculated with the central component of the interactions are of positive sign. By adding spin-orbit part to central part of the interactions, sign of the total NMEs gets change, and in absolute value, NMEs decreases by about 15–18%. Sign change in total NMEs are again seen by adding tensor part to the central+spin−orbit part of the interactions. Similar trends of sign change are also observed for Fermi, Gamow-Teller, and tensor matrix elements. Thus we infer that SO and T part mostly cancel the effects of each other in NMEs calculations. For both the interactions, the total NMEs calculated with the C part is found to be 20% enhanced as compared to the NMEs calculated with the total interactions. With new GX1R interaction, there is about 1–3% increments in the total NMEs as compared to NMEs with GXPF1A interaction. This increments comes from the modifications of isospin T = 1 tensor force two-nucleon matrix elements to bring the characteristic properties of tensor force into the GX1R interaction.