Scope of the meeting

Topics of the Workshop

Physics case

Hadron structure from QCD on the lattice

Hadrons are composed of quarks and gluons, which interact in a complex way to form bound- and resonance states of color singlets. It is of paramount importance to understand the non-perturbative mechanisms for the formation of these states from first principles. Important contributions are made by numerical simulations of QCD, which begin to provide a degree of accuracy such that quantitative comparisons with experiment become possible.

Structure of the nucleon

Of particular interest is the internal structure of the nucleon, as probed by leptons in a wide range of Q^2 and Bjorken x. The experimental programs at ELSA, MAMI and JLAB provide important insights on low-momentum form factors and the role of the pion cloud, the onset of QCD scaling and the spatial- and momentum distributions of quarks in the nucleon. The origin of the nucleon spin remains a central problem in experimental and theoretical studies with high-energy leptons at COMPASS, RHIC and the planned EIC, for instance. This closely relates to the gluon distribution functions, for which a detailed understanding is still lacking.

Glueballs, hybrids and multi-quark states

Based on quark models it has long been suggested that there should exist hadrons composed not only of quark-antiquark states or three-quark states but also hadrons consisting of genuine "multi-quark" configurations might exist. An alternative explanation for such states is the existence of "hadronic molecules" as bound- or resonant color singlet hadrons. The interplay between these descriptions of observed data remains the focus of current debates. QCD predicts the existence of hadrons purely made of gluons, so-called "Glueballs". There are many theoretical indications for the existence of such states, but they have not yet been identified experimentally. A possible explanation is that Glueballs strongly mix with quark-antiquark states and hence acquire a large width. Glueball searches and multi-quark spectroscopy will be a central part of the future PANDA project at FAIR in proton-antiproton annihilation experiments.

Heavy quark physics

Experiments at Belle II, BESIII and LHCb for charmonium and bottomonium systems have revealed a rich spectrum of narrow states slightly above threshold that came as a total surprise. The origin of these states and their detailed structure remains a challenge to experiment and theory.

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