The CLXXX Course, “Three-Dimensional Partonic Structure of the Nucleon”, of the “Enrico Fermi” School, held in Varenna from June 28 to July 8, 2011, was devoted to the study of the 3-dimensional structure of protons and neutrons (nucleons) and to the properties and motion of the nucleon internal constituents, quarks and gluons (partons).
This issue is central in many theoretical and experimental activities and has marked a real transition, in the last two decades, in our exploration of the ultimate structure of matter, addressing fundamental questions such as the orbital motion of quarks and gluons inside the nucleons, their spatial distribution and the correlation between spin and intrinsic motion. A real 3-dimensional imaging of the nucleon as a composite object, both in momentum and coordinate space, is slowly emerging.
Several dedicated experiments are either running (COMPASS, JLab and RHIC) or analyzing previously collected data (HERMES). Other experimental facilities are under construction (J-PARC and the upgrading of JLab) or being planned (PANDA, PAX, ENC, EIC). All these have a central focus in the study of the 3-dimensional nucleon structure.
Enormous theoretical progress has been achieved in the last years with the new concepts of Transverse Momentum Dependent (TMDs) and Generalized Parton Distributions (GPDs). These can be studied respectively in inclusive and exclusive processes at the above-mentioned facilities by looking at spin asymmetries and azimuthal distribution of final hadrons or leptons. The collection and interpretation of data, with theorists and experimentalists working together, is and will be one of the major activities in hadron physics; the international scientific community working in the field is constantly growing.
The proposed School had the ambitious goal of educating postgraduate students, so that they could end up becoming specialists in hard scattering and partonic azimuthal distributions analysis and could be able to join CLAS, COMPASS, RHIC, J-PARC, PAX, PANDA, EIC, ENC and any of the dedicated experiments; or they could perform theoretical and phenomenological studies of TMDs and GPDs.
The School was attended by 40 students and 3 observers from 13 different Countries. Basic introductory lectures were delivered by 7 lecturers and more specialized topics covered by 7 seminar speakers. All of them are among the world experts in their own field. Special attention was given to the interaction among lecturers and students and to favor active participation. Lectures and seminars were focused on the conceptual theoretical ideas, the experimental techniques and the phenomenological interpretation of data. Special lectures and tutorials were dedicated to data analysis and model building, with the active participation of students.
The main topics discussed can be summarized as follows:
– Partonic distributions, fragmentation functions and factorization in QCD (collinear case).
– Theory of Transverse Momentum Dependent partonic distributions (TMDs).
– Theory of Generalized Partonic Distributions (GPDs).
– Experimental methods in studies of hard scattering processes.
– Extraction of TMDs and GPDs from data.
– Analysis tools for azimuthal asymmetries.
– Models for TMDs and numerical methods.
– Future experiments.
In conclusion the organizers of the Course warmly thank the Jefferson Science Associates, the Jefferson Laboratory, and the HadronPhysics2 European Project of the FP7 framework for their generous financial support; the Wolfram Research for supporting the School with complimentary licenses of Mathematica for Students. Special thanks are due to Barbara Alzani, Monica Bonetti, Roberta Comastri and Ramona Brigatti for their precious, continuous and invaluable help both during the preparation of the Course and its organization at Villa Monastero.
M. Anselmino, H. Avakian, D. Hasch and P. Schweitzer