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The three-dimensional quark-gluon structure of the nucleon

The theoretical study and the experimental exploration of the internal structure of protons and neutrons (nucleons) have recently entered a new phase. Over the past 40 years an understanding of nucleons in terms of elementary constituents (partons, i.e. quarks and gluons) has gradually and successfully emerged. Much has been learned about the nucleon in terms of its “one-dimensional” parton structure, relevant when partons are assumed to move co-linearly with their parent nucleon, and encoded in the so-called parton distribution functions (PDFs). In the last few years theoretical breakthroughs have extended this simple picture, leading to new concepts, like the “Generalized Parton Distributions” (GPDs) and the “Transverse Momentum Dependent parton distributions” (TMDs). These concepts help to address long-standing questions concerning the motion of quarks and gluons inside the nucleon, their orbital motion, their spin and their spatial distribution. Dedicated experiments, either running or proposed, and a related intense theoretical activity have made, and keep making, enormous progress towards a true 3-dimensional unraveling of the nucleon structure. Our aim is to continue our participation in this program of collaboration.


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Petr Závada