EPJ A Highlight - Nuclear physics with a medium-energy Electron-Ion Collider

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Published on 21 October 2012

Quarks and gluons are the fundamental constituents of most of the matter in the visible Universe; Quantum Chromodynamics (QCD), a relativistic quantum field theory based on color gauge symmetry, describes their strong interactions. The understanding of the static and dynamical properties of the visible strongly interacting particles - hadrons - in terms of quarks and gluons is one of the most fascinating issues in hadron physics and QCD. In particular the exploration of the internal structure of protons and neutrons is one of the outstanding questions in experimental and theoretical nuclear and hadron physics. Impressive progress has been achieved recently.

The paper, clearly and concisely, addresses several of the issues related to the microscopic structure of hadrons and nuclei: (i) the three–dimensional structure of the nucleon in QCD, which involves the spatial distributions of quark and gluons , their orbital motion, possible correlations between spin and intrinsic motion; (ii) the fundamental color fields in nuclei (nuclear parton densities, shadowing, coherence effects, color transparency); (iii) the conversion of color charge to hadrons (fragmentation, parton propagation through matter, in–medium jets).

The conceptual aspects of these questions are briefly reviewed and the measurements that would address them are discussed, with emphasis on the new information that could be obtained with experiments at an electron-ion collider collider (EIC). Such a medium–energy EIC could be realized at Jefferson Lab after the 12 GeV upgrade (MEIC), or at Brookhaven National Lab as the low–energy stage of eRHIC.