Freiburg 2008 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 27: QCD IV

T 27.3: Vortrag

Freitag, 7. März 2008, 14:35–14:50, KGI-HS 1021

DVCS at HERMES — •Caroline Riedl for the HERMES collaboration — DESY/Zeuthen, Germany

The HERMES experiment at DESY, Hamburg used the HERA polarized electron or positron beam with an energy of 27.6 GeV to scatter off polarized or unpolarized pure gas targets (H, D or heavier nuclei). In the past 11 years, the experiment has collected a rich data set for the analysis of Deeply Virtual Compton Scattering (DVCS).
The azimuthal asymmetries measured for the exclusive DVCS reaction allow to access the imaginary and/or real part of certain Generalized Parton Distributions (GPDs). Those GPDs are of great theoretical interest as they embody both spatial and momentum density information of the quarks and gluons making up the nucleon. Moreover, in a certain kinematic limit, certain moments of the quark (gluon) GPDs E and H deliver the total angular momentum carried by quarks (gluons) in the nucleon.
Until the year 2005, the recoiling target nucleon from the DVCS reaction was not detected. Exclusivity was ensured indirectly by a missing-mass-technique. In 2006 and 2007, data were taken with a new Recoil Detector installed around the HERMES target region. The Recoil Detector can identify the recoiling target nucleon and the particles from underlying background processes and can thus be used to directly tag exclusive events and to reject background channels. An overview over DVCS results will be shown and first results from the HERMES Recoil Detector will be presented.