Arnaldo Pomodoro Sfera n.6

2nd Workshop on the QCD Structure of the Nucleon

June 12-16, 2006

Villa Mondragone Monte Porzio Catone, Rome, Italy

A. Pomodoro, Sfera n.6


Among the presently most interesting topics in hadron physics, besides inclusive deep-inelastic scattering, are exclusive photon or meson and semi-inclusive meson electroproduction. They constitute the main focus of the current generation of fixed-target facilities at CERN (COMPASS), DESY (HERMES) and JLab. Their ongoing and planned measurements, in conjunction with the upcoming nucleon spin results from proton-proton collisions at RHIC, will significantly improve the knowledge on the spin structure of the nucleon.

Information on the longitudinal (helicity) spin structure, recently explored for valence and also sea quarks by HERMES, will be soon complemented by new results on the gluon contribution to the nucleon spin. More accurate information is expected soon on the Sivers distribution and Collins fragmentation functions, as well as new data on hitherto unmeasured transversity distribution functions describing the transverse spin structure of the nucleon.

On the other hand, by studying (quasi-) exclusive reactions HERMES, JLab, H1 and ZEUS have made first steps into the unexplored field of Generalized Parton Distributions (GPDs). These are non-perturbative, process-independent, multi-variable distribution functions which occur in the description of a variety of different hard processes, from inclusive to hard exclusive scattering. GPDs can also be accessed in wide-angle exclusive processes, such as real Compton scattering, and in the time-like region. GPDs are of interest to theory and experiment because they open access to the angular momentum of the partons inside the nucleon. Here, only a very first experimental result from HERMES exists till now. Lattice gauge theory recently provided first reliable results on intrinsic and orbital angular momenta of u and d-quarks. Phenomenological analyses already provided information on the GPDs at zero skewness. Global fits to data from several independent deeply virtual exclusive reactions may later allow for an extraction of the GPDs at non-zero skewness.

The workshop on "The QCD Structure of the Nucleon" will address the present status and the future of the field, as sketched above. The close connection between experiment and theory will be accounted for by discussing theoretical interpretation and modeling of the data, and the status of Effective Field Theory and Lattice QCD. Common efforts towards accessing Generalized Parton Distributions, as well as theoretical and experimental efforts towards measuring new distribution and fragmentation functions (in particular the transversity distributions) will play a major role in the workshop. The workshop will be completed by presentations of projects planned all over the world at future high performance facilities for studying the nucleon spin structure.

Physics Topics:

  • Exclusive Reactions and Generalized Parton Distributions
  • Distribution and Fragmentation Functions. Transversity
  • Future facilities

Last edited by F. Ronchetti, November 9, 2005