Separation of structure functions and electron distortion in quasifree (e, e′p) reactions

In the one-photon exchange approximation the coincidence cross section of the quasifree (e, e′p) reaction can be written in terms of four structure functions, which represent the response of the nucleus to the various components of the electromagnetic interaction. The role of Coulomb distortion of electrons on the separation of these structure functions is investigated. The distorted-electron wave functions are given by an expansion in powers of Zα, whose validity is discussed. The effect of electron distortion on the separation of longitudinal and transverse responses in parallel kinematics is considered, taking 40Ca and 208Pb as study cases. The effect is found to be significant. However, whereas for 40Ca it can be eliminated, with a good degree of accuracy, by correcting the cross section through effective momentum transfer, in 208Pb also large contributions due to the focusing of the electron wave must be carefully subtracted. The determination of longitudinal-transverse interference structure function in coplanar perpendicular kinematics is also discussed.