Quasi-elastic Scattering and Coincidence Reactions

In the impulse approximation, the (e,ep) cross section is the product of an off-shell electron-proton cross section times the nucleon momentum distribution. It is of great interest to pursue this reaction to the most extreme kinematical situations, namely high and high internal nucleon momenta. Recently, the deuteron momentum distribution has been determined at SLAC for momentum transfers up to =6.8 (GeV/c). This represents well over an order of magnitude increase over previous intermediate-energy results. The momentum distributions are extracted from these data [Br94] by dividing out the kinematic factor and the (covariant) ``cc1''e-p cross section. The so obtained are shown in Figure compared to a calculation employing the Bonn potential. The agreement is quite reasonable. One concludes that the basic wavefunction of the deuteron is fairly well understood and that the dominant feature of the reaction process, quasi-elastic electron-nucleon scattering, appears under control (this is less true for individual response functions than it is for the total cross section).

Perhaps the most attention recently has been focused on the interference response function . The data are typically presented as the left- right asymmetry . Results are available at low from both NIKHEF and MIT/Bates and at high (1.2 (GeV/c)) from SLAC. The latter results are shown in Figure . Both the low and high data indicate a clear preference for a relativistic treatment of this observable. That proper relativistic treatment of the electron- nucleon vertex is the dominant effect is further evidenced by the dotted curve shown with the SLAC data. This is simply times a non- relativistic momentum distribution. As can be seen, it provides a description of the data that is comparable to the other, more sophisticated treatments.