Microscopic calculation of two-particle-two-hole meson-exchange currents in 40Ar and asymmetric scaling properties for neutrino and electron scattering

Abstract

We present a microscopic calculation of two-particle–two-hole meson-exchange current response functions in asymmetric nuclei, with particular emphasis on the 40Ar nucleus. Employing a relativistic mean-field and relativistic Fermi gas framework, we compute the nuclear response for 40Ar and compare it with that of the symmetric 40Ca nucleus, analyzing the role of proton-neutron imbalance. The model incorporates distinct proton and neutron Fermi momenta to accurately capture the nuclear dynamics of systems with Z ≠ N. Our results indicate that using 40Ca as a proxy for 40Ar leads to a systematic error of approximately 10%. Additionally, we propose an asymmetric scaling formula to obtain the two-particle–two-hole response for arbitrary nuclei from the 12C response, improving the description of asymmetric nuclei. Finally, we benchmark our predictions against inclusive electron scattering and neutrino cross sections.