[en] Selected results of diffractive vector meson leptoproduction and inclusive deep-inelastic lepton scattering are presented. The data have been obtained by the HERMES collaboration using polarized ¹H, ²H, ³He, and unpolarized ¹⁴N targets that were internal to the HERA 27.5 GeV positron beam. Three topics are addressed: (i) The longitudinal part of the ρ⁰ production cross section is shown to be fairly well described by a pQCD calculation based on the Off-Forward Parton Distribution (OFPD) framework; (ii) The ρ⁰ production data reveal a non-zero asymmetry with respect to the spin orientation of the ¹H target; and (iii) The ratio of inclusive deep-inelastic scattering data on ¹⁴N (or ³He) and ²H targets shows a surprising deviation with respect to existing NMC and E665 data on ¹²C, which is interpreted in terms of an A-dependence of the quantity R σ_L/σ_T

[en] In this thesis the results of an investigation into two aspects of the mechanism of the quasi-elastic (e,e'p) reaction: the interaction between the incident electron and the bound proton and the residual nucleus (final-state interaction (FSI)), are presented and used in the extraction of nuclear-structure information from (e,e'p) measurements on ¹²C. The experiments were carried out at NIKHEF-K with a high-resolution spectrometer. Two kinds of experiments have been performed on ¹²C. The first was aimed at obtaining accurate momentum distributions for various final states in ¹¹B. Some special measurements were carried out in order to vary the parameters influencing the FSI. The role of coupled-channels effects in the ¹²C(e,e'p)¹¹Be reaction is discussed. It is discussed whether some of the weak transitions observed in this reaction, can be associated with knockout from normally unoccupied shell-model orbitals. The second experiment on ¹²C was devoted to the e-p coupling. These measurements were supplemented with data taken on ⁶Li. The latter measurement allowed for measuring simultaneously knockout from the relatively dense ⁴He core and the relatively dilute deuteron. In this way the density dependence of the e-p coupling in the nucleus could be studied. The results of these experiments have been compared to various models that take into account the effect of the nuclear medium upon the e-p coupling. The possible role of charge-exchange and meson-exchange currents in the interpretation of these experiments is also considered. A brief survey of the formalism of the quasi-elastic (e,e'p) reaction is also presented. (author). 196 refs.; 53 figs.; 21 tabs

[en] The production of mesons (or photons) in deep-inelastic lepton scattering gives access to information on the structure of hadrons that is otherwise hard to obtain. When the production process involves at least one hard scale and is exclusive, the data can be interpreted in terms of the recently introduced generalized parton distributions (GPDs). These GPDs provide a unified description of hadronic structure, which can be applied to many different reactions. It will be shown how new data collected by the HERMES experiment at DESY are used to obtain first information on GPDs. Examples of hard exclusive processes observed at HERMES include the production of pseudoscalar and vector mesons, and deeply-virtual Compton scattering

[en] Fixed target experiments at future deep-inelastic scattering facilities, such as the proposed TESLA-N and EVELIN projects, require the detection of particles at larger angles than will be covered by the forward-angle spectrometers, typically foreseen in such high-luminosity experiments. The large-angle particles mostly correspond to recoil protons that can be used to identify exclusive processes, which currently are of high interest as they give access to the Generalized Parton Distributions. For this purpose a large-angle detector needs to be developed. The resolution and particle identification capability that can be achieved with a small detector consisting of a few silicon layers has been investigated. The detector is assumed to perform multiple sampling of the ionization tracks caused by high momentum (<2 GeV c^-1) pions, kaons, and protons in the silicon. Realistic models for the noise of the read-out electronics and segmentation of the detectors are used. The result of the study which is based on Monte Carlo simulations and--partly--calibrated by data, is a conceptual detector design with π, p, K separation up to 1.3 GeV c^-1

[en] A review is given of new ²H(e,e'p) data that include a determination of individual structure functions. Two experiments performed in quasi-elastic (inplane) kinematics at NIKHEF-K provided data for the longitudinal, transverse and longitudinal-transverse interference structure functions, f₀₀, f₁₁, and f₀₁. The f₀₁ data show the need for a calculation that treats the electro-disintegration process in a consistent relativistic framework at surprisingly low momentum transfer values (460 MeV/c). A third experiment performed at Tohoku University has measured for the first time the transverse-transverse interference structure function f_-11 using an out-of-plane detection system. (author)

[en] A review is given of recent results obtained in quasi-elastic (e,e'p) experiments performed at MIT/Bates, NIKHEF and Saclay. Both the possible modification of the electron-proton coupling in the nuclear medium and the effects of long- and short-range correlations are discussed. (orig.)

[en] The recent experiments carried out at the Bates Linear Accelerator Center, involving (γ,p), (γ,n) and (γ,π^-p) reactions on ¹⁶O are discussed, as well as some possible future experiments. 41 refs, 5 figs

[en] The HARP detection system is a novel device which can be used for both neutron detection and for the determination of neutron and proton polarizations in nuclear physics experiments. It is currently under construction by the HARP collaboration, comprising Utrecht University, ISN-Grenoble and NIKHEF-Amsterdam. The instrument will be completed in 1995. A brief description of HARP is given. (author)

[en] A selection of new data obtained by the HERMES experiment at DESY is presented, which provides new insight into the QCD structure of the nucleon. Using polarized lepton beams and polarized targets, the spin-dependent structure function g₁(x) has been determined for ¹H, ²H and ³He. By also observing one of the produced hadrons it has been possible to extract the polarization distribution of individual quark flavours in the nucleon as well. Further information on nucleon structure has been obtained by observing (almost) exclusive reactions, which can be interpreted in terms of the recently introduced generalized parton distributions (GPDs). As an example of such data measurements of both the beam-spin and beam-charge asymmetries resulting from deeply virtual Compton scattering (DVCS) are presented. By embedding the deep-inelastic scattering process in the nuclear environment additional information can be obtained on nucleon structure and some QCD effects. The potential of this technique is illustrated by showing new results on tagged structure functions and hadronization in nuclei. (orig.)

[en] Quantum Chromodynamics (QCD) provides the framework for our understanding of the strong interaction, and is therefore at the basis of our understanding of nuclear physics. The difficulty encountered when applying QCD to the length scales appropriate for nucleons, however, is the fact that the perturbative techniques used to solve QCD at high energies cannot be used. Nevertheless considerable progress is being made in this domain through a series of very precise experiments that were analysed in a QCD framework. In this way the quark-gluon structure of hadrons has been investigated successfully. In recent years these studies were extended in various directions. Striking results in the areas of hadron spectroscopy and hadron form factors revived the interest in the corresponding experiments, while the (theoretical) introduction of the transverse spin distributions and the generalized parton distributions led to a whole set of newly proposed experiments. Initial results obtained in each of these areas of research are used to illustrate likely future directions of experiments aimed at unraveling the QCD structure of the nucleon