Berlin 2005 – scientific programme

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T: Teilchenphysik

T 208: Diffraktion

T 208.2: Talk

Friday, March 4, 2005, 14:15–14:30, TU H3002

A Measurement of Deeply Virtual Compton Scattering with HERA II data — •Raquel Santamarta^1,2 and Uta Stösslein¹ — ¹DESY Hamburg — ²Universität Hamburg

At HERA II, longitudinally polarized electrons and positrons collide with unpolarized protons at centre-of-mass-energies of 318 GeV and at high luminosities. This offers unique opportunities to investigate new observables as provided by deeply virtual, or off-forward, Compton scattering (DVCS). The DVCS process has been revelead as one of the most promissing tools to obtain new information about the structure of the nucleon via generalised parton distributions (GPDs).

Using the ZEUS detector at HERA II, the DVCS related beam-spin and beam-charge asymmetries can be measured in addition to the DVCS cross section. In contrast to existing DVCS asymmetry measurements from the fixed target experiments HERMES and CLAS, this analysis explores a new kinematic range of high γ^⋆p c.m.s. energies of ∼ 90 GeV and small Bjorken-x<0.01 values.

The feasibility of such new asymmetry measurements will be presented based on data taken in 2003/2004 with ZEUS. The data taking and trigger efficiencies as well as related systematics and resolutions studies will be shown. First results for the beam-spin asymmetry using positrons will be presented.