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HK: Physik der Hadronen und Kerne

HK 36: Hauptvortr
äge

HK 36.3: Invited Talk

Wednesday, March 9, 2005, 11:15–11:45, TU MA001

Present understanding of single spin asymmetries — •Andreas Metz — Institut für Theoretische Physik II, Ruhr-Uni Bochum

The talk summarizes the intriguing physics of single spin asymmetries in hard scattering processes by focussing on the recent developments. Currently such asymmetries are studied in semi-inclusive lepton-nucleon scattering at DESY (HERMES Collaboration), at CERN (COMPASS Collaboration), and at the Jefferson Laboratory. Measurements in proton-proton collisions are performed at RHIC.

It is known for a long time that socalled time-reversal odd correlation functions (parton distributions and fragmentation functions) can generate single spin asymmetries. But only recently it was shown that T-odd parton distributions don’t vanish, where the presence of the Wilson line in the operator definition, which ensures color gauge invariance, plays a crucial role. In addition to this issue we discuss the universality of T-odd correlation functions, the discovery of previously unknown T-odd functions at subleading twist, and an interesting connection between single-spin phenomena and generalized parton distributions.