High Resolution Quasi-Free (e,e′p) Experiments

Abstract

The purpose of these lectures is to provide an introduction to recent state-of-the-art developments in the field of the quasi-free proton-knock-out process induced by high-energy (=500 MeV) electrons. In the electron scattering (e,e′) response function d²σ/dΩde′ of a nucleus the quasi-free process becomes the dominant feature when the wavelength of the virtual photon becomes of the order of the nucleon dimension δ r=0.8 fm. Since the average internucleon distance amounts to = 2 fm and provided that the mean free path of the knocked-out nucleon is substantially larger than the internucleon distance, the dominant reaction mechanism involves incoherent scattering off individual (quasi-free) nucleons. In this incoherent scattering limit the probability distribution of momentum and energy of the struck nucleon can be reconstructed if a coincidence (e,e′p) experiment is performed. Due to the, in principle, straightforward simplicity of interpretation the quasi-free process has found widespread application in diverse fields varying from the few kilo electron volt (e,2e) process¹ at the level of atomic dimensions, to the deep-inelastic scattering of multi-GeV electrons from point-like constituents (partons) in the nucleon.²