Abstract. Quark-hadron duality addresses some of the most fundamental issues in strong interaction physics, in particular the nature of the transition from the perturbative to non-perturbative regions of QCD. I summarize recent developments in quarkhadron duality in lepton-hadron scattering, and outline how duality can be studied at future high-luminosity facilities such as Jefferson Lab at 12 GeV or an electron-hadron collider such as EPIC. I INTRODUCTIONUnderstanding the structure and interaction of hadrons in terms of the quark and gluon degrees of freedom of QCD is the greatest unsolved problem of the Standard Model of nuclear and particle physics. If one accepts QCD as the correct theory of the strong interactions, then the transition from quark-gluon to hadron degrees of freedom should in principle amount to a change of basis, with all physical quantities independent of which basis is used. However, although the duality between quark and hadron descriptions is formally exact, in practice the necessity of truncating any Fock state expansion means that the extent to which duality holds reflects the validity of the truncations under different kinematical conditions and in different physical processes. Quark-hadron duality is therefore an expression of the relationship between confinement and asymptotic freedom, and is intimately related to the nature of the transition from non-perturbative to perturbative QCD.In nature, the phenomenon of duality is in fact quite general and can be studied in a variety of processes, such as e + e − → hadrons, or heavy quark decays [1]. One of the more intriguing examples, initially observed some 30 years ago, is in inclusive inelastic electron-nucleon scattering.

New Jefferson Lab data are presented on the nuclear dependence of the inclusive cross section from (2)H, (3)He, (4)He, (9)Be and (12)C for 0.3 < x < 0.9, Q(2) approximately 3-6 GeV(2). These data represent the first measurement of the EMC effect for (3)He at large x and a significant improvement for (4)He. The data do not support previous A-dependent or density-dependent fits to the EMC effect and suggest that the nuclear dependence of the quark distributions may depend on the local nuclear environment.

We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate.

Quantum chromodynamics (QCD), the microscopic theory of strong interactions, has not yet been applied to the calculation of nuclear wavefunctions. However, it certainly provokes a number of specific questions and suggests the existence of novel phenomena in nuclear physics which are not part of the traditional framework of the meson-nucleon description of nuclei. Many of these phenomena are related to high nuclear densities and the role of colour in nucleonic interactions. Quantum fluctuations in the spatial separation between nucleons may lead to local high-density configurations of cold nuclear matter in nuclei, up to four times larger than typical nuclear densities. We argue here that experiments utilizing the higher energies available upon completion of the Jefferson Laboratory energy upgrade will be able to probe the quarkgluon structure of such high-density configurations and therefore elucidate the fundamental nature of nuclear matter. We review three key experimental programmes: quasi-elastic electro-disintegration of light nuclei, deep inelastic scattering from nuclei at x > 1 and the measurement of tagged structure functions. These interrelated programmes are all aimed at the exploration of the quark structure of high-density nuclear configurations.The study of the QCD dynamics of elementary hard processes is another important research direction and nuclei provide a unique avenue to explore these dynamics. In particular, we argue that the use of nuclear targets and large values of momentum transfer at energies available with the Jefferson Laboratory upgrade would allow us to determine whether the physics of the

Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this Letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5  GeV2. By extending the range of Q2 for which G(E)(p) is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the nonperturbative regime.