Microscopic optical potentials for calcium isotopes

Abstract

We construct nucleonic microscopic optical potentials by combining the Green's function approach with the coupled-cluster method for 40Ca and 48Ca. For the computation of the ground states of 40Ca and 48Ca, we use the coupled-cluster method in the singles-and-doubles approximation, while for the A = ±1 nuclei we use particle-attached and particle-removed equation-of-motion method truncated at two-particle–one-hole and one-particle–two-hole excitations, respectively. Our calculations are based on the chiral nucleon-nucleon and three-nucleon interaction NNLOsat, which reproduces the charge radii of 40Ca and 48Ca, and the chiral nucleon-nucleon interaction NNLOopt. In all cases considered here, we observe that the overall form of the neutron scattering cross section is reproduced for both interactions, but the imaginary part of the potential, which reflects the loss of flux in the elastic channel, is negligible. The latter points to neglected many-body correlations that would appear beyond the coupled-cluster truncation level considered in this work. We show that, by artificially increasing the parameter η in the Green's function, practical results can be further improved.