Inclusive electron scattering from 2H,3He, and 4He.

We present new results for inclusive electron scattering in $^{2}\mathrm{H}$, $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ in order to test the reaction mechanism for quasielastic scattering as a function of nuclear density. Radiative corrections are applied to the cross section data and Rosenbluth separations are made for three-momentum transfer (q) between 300 and 600 MeV/c. The A and q dependencies of the data are discussed for the quasielastic peak and the region between the quasielastic peak and the \ensuremath{\Delta} resonance peak (dip region). Comparisons are shown between the data and models based on a quasielastic reaction mechanism. The models give a reasonable representation of the peak at q\ensuremath{\sim}500 MeV/c, but the longitudinal data for the helium isotopes are significantly suppressed with respect to the quasielastic predictions at q<400 MeV/c. None of the calculations predict the rapid rise with q and A in the transverse strength in the dip region seen in the data. A significant breakdown of the quasielastic picture is seen in the data as A increases from 2 to 4.