Density dependence of 2p-2h meson-exchange currents

We analyze the density dependence of the contribution of meson-exchange currents to the lepton-nucleus inclusive cross section in the two-particle two-hole channel. The model is based on the relativistic Fermi gas, where each nucleus is characterized by its Fermi momentum k F . We find that the 2p-2h nuclear response functions at their peaks scale as Ak F 2 for Fermi momentum going from 200 to 300 MeV/c and momentum transfer q from 2k F to 2 GeV/c. This behavior is different from what is found for the quasielastic response, which scales as A/k F . Additionally, the deep scaling region is also discussed and there the usual scaling behavior is found to be preferable.