First Measurement of the Imaginary Part of the Transverse-Longitudinal Nuclear Response.
We have measured a new electron scattering observable, the fifth'' structure function, [ital f][sub 01][sup [prime]], which is the imaginary part of the transverse-longitudinal interference response. Its observation requires a longitudinally polarized beam and coincident, out-of-plane particle detection. [ital f][sub 01][sup [prime]] arises from interference between reaction channels and provides an additional means for their disentanglement. In the quasielastic [sup 12]C([ital [rvec e]],[ital e][prime],[ital p]) measurements reported here, [ital f][sub 01][sup [prime]] is driven by the interference of the direct knockout and rescattering amplitudes.