0νββ decay of 136Xe using the nonclosure approach in the nuclear shell model

In this investigation, we compute the nuclear matrix elements (NMEs) relevant to the light neutrino-exchange mechanism governing neutrinoless double beta (0 nu beta beta) decay in 136Xe. Our method is based on the nonclosure approach within the interacting nuclear shell model framework. This approach considers the genuine effects arising from the excitation energies of the first 200 states for each spin-parity of the intermediary nucleus 136Cs. All computations are performed using the effective shell model Hamiltonian GCN5082. To understand the impact of nuclear structure on 0 nu beta beta decay, we explore the dependence of the NME on various factors, including the number of intermediate states and their spin-parity characteristics. We identify an optimal closure energy of approximately 3.7 MeV for the 0 nu beta beta decay of 136Xe that reproduces the nonclosure NME using the closure approach. The calculated total NME for the light neutrino-exchange 0 nu beta beta decay of 136Xe is 2.06 with the CD-Bonn short-range correlation. These results can be valuable for future experimental investigations into the 0 nu beta beta decay of 136Xe.