Physics with a GeV-electron accelerator

A systematic review and theoretical analysis of the experimental data on multi GeV lepton, photon, hadron, deuteron (nucleus) reactions from nuclei forbidden in the case of scattering from free nucleons is presented. It is shown that all these data can be quantitatively described as a manifestation of short-range few nucleon correlations. Calculations for elastic and (deep)inelastic electromagnetic and weak form factors of the deuteron and other nuclei, are given. The inclusive production of leading particles in the nucleus fragmentation region in high-energy lepton, hadron or nucleus-induced collisions is analyzed. The straightforward correspondence between the Weinberg equation for the light-cone wave functions of the deuteron and the non-relativistic Schrödinger equation is found. It is shown that the predictions of quantum chromodynamics for short-distance phenomena in nuclei are in agreement both with experimental data and theoretical expectations due to short range correlations in nuclei. Several feasible experiments are considered which could establish the existence of relativistic nuclear physics.

The perspectives of Nuclear Research with electromagnetic probes are widely determined by the characteristics of the new generation of electron accelerators; the machines to be built in the future will be characterized by two parameters which for the following discussion will be quite relevant: - $\text{high duty cycle}$ (up to 100 per cent); this will allow to perform systematically coincidence experiments, which have been quite difficult and timeconsuming at the presently available machines; - $\text{high end point energies}$ (up to one or several GeV); this will lead us into a new field of Nuclear Physics, which is related to the excitation of the internal or subnucleonic degrees of freedom of a bound nucleon.

Quite naturally, this report will, therefore, be concentrated on two topics: (i) the discussion of coincidence experiments, especially of the (e,e'x) reaction as a tool to investigate nuclear properties; here, two types of mechanisms will be dealt with: the direct and the resonance reaction, respectively; (ii) the discussion of the physical phenomena that can be exploited at medium energies; as a convenient ordering parameter we will use the excitation energy which is deposited onto the nucleus in such an (e,e') reaction.

We emphasize one particular aspect which we find most attractive, both from a conceptual and from a phenomenological point of view: the (electro)excitation of the subnucleonic (or quark) degrees of freedom of a nucleon bound in a complex nucleus; in this energy domain a new frontier of Nuclear Research is presumably going to open up: the investigation of the nuclear analogues of the elementary N^∗-resonances; their properties are related both to the internal (or quark-) structure of the baryon and to the interaction between two and more baryons with each other. The corresponding many body modes of motion are obviously rather complicated; their investigation necessitates a careful analysis of highly exclusive experiments. The explanation of the corresponding excitation spectrum, however, is quite essential for a deeper understanding of the dynamics of a system of strongly interacting particles.

Some basic problems in nuclear physics which may receive positive response from electro- and photonuclear research, are discussed. Future directions for this research are outlined and some specific experimental proposals compiled by a study group under the sponsorship of the Bates (MIT) Users Group are described.