Longitudinal response functions for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been obtained from inclusive electron scattering cross sections, for $200\le q\le 550$ MeV/c. The response functions are compared with several theoretical calculations, all of which use exact three-body ground-state wave functions. The response functions are found to be more similar than the calculations predict. When a direct calculation of the Coulomb sum rule is compared with our data, the agreement is good and evidence for two-proton correlations in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is clear.

• Received 9 March 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1706