A variational Monte Carlo approach for the study of medium-mass nuclei

We report on an accurate variational many-body technique (cluster variational Monte Carlo) suitable for the study of medium-mass nuclei. The employed many-body nuclear Hamiltonian contains realistic two- and three-nucleon interactions and the trial wave function is constructed from pair- and triplet-correlation operators acting on a product of single-particle determinants. As opposed to traditional variational Monte Carlo calculations, that are limited to $A=12$ nuclei, expectation values are evaluated with a cluster expansion for the non-central correlations. The cluster expansion drastically reduces the computational effort necessary for the study of an $A$-body system, allowing us to extend the calculations in the medium-mass region, currently up to $40$ nucleons. We present results for the closed-shell nuclei $^{16}$O and $^{40}$Ca and prospects for open-shell nuclei like $^{40}$Ar. Of particular interest is the derivation of the momentum distributions that can be used to constrain the spectral functions of these nuclei. This has a crucial interplay with electron-nucleon and neutrino-nucleon scattering experiments, where Argon is among the typical targets and the scattering data at high momentum transfer can be analyzed by means of the spectral function formalism.