and 
mesons in the scattering of 160 GeV polarized muons on nucleons or nuclei from the COMPASS polarized target.
A recent renewed interest in studying exclusive precesses in deep inelastic leptoproduction is related to a new direction of studies of the quark and gluon structure of nucleons in terms of Generalised Parton Distributions – (GPDs), which provide a complete description of the partonic structure of the nucleon. GPDs, which embody correlations of the momentum and space distributions of quarks and qluons, allow, for instance, a new description of the nucleon as an extended object, as well as provide an insight on the role of the orbital angular momentum of quarks in explaining the proton spin.
Although the theoretical studies of GPDs are well advanced, the available experimental information is still limited. Beside the GPD studies started few years ago by experiments in the Jefferson Laboratory (USA) and by the HERMES experiment at DESY, COMPASS is presently the only experiment, which will provide the data at higher energy and in a wider kinematical range.
Studies of diffractive processe at STAR encompass both elastic proton-proton scattering as well as various processes of inelastic diffraction. Among the later ones the the central production is particularly interesting, when hadrons are produced only in the central region (rapidity y≈0) and both protons are subject only to slight changes of their momenta. Centrally produced hadrons may originate from a production of exotic particles (e.g. glueballs) or from a production of a pair of gluonic jets with large transverse momenta. The unique feature of RHIC, in contrast to other colliders, is possibility to polarise proton beams, which provides a possibility to study the role of the spin in the mentioned processes.
More information:
Assoc. Professor Andrzej Sandacz
The Andrzej Soltan Institute for Nuclear Studies
High Energy Physics Department
69 Hoża st.
Warszawa, Poland
phone ++(4822) 5532207
Andrzej.Sandacz@fuw.edu.pl