Dresden 2013 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 27: Hadronenstruktur und -spektroskopie

HK 27.7: Vortrag

Dienstag, 5. März 2013, 15:45–16:00, HSZ-101

Measurements of azimuthal asymmetries in DVCS and associated processes at HERMES — •Erik Etzelmüller, Avetik Airapetian, Irina Brodski, Michael Düren, and Marian Stahl — II.Physikalisches Institut, Justus-Liebig-Universität Gießen, 35392 Gießen, Germany

Azimuthal asymmetries in exclusive electroproduction of real photons by the longitudinally polarized Hera positron beam scattering off an unpolarized hydrogen target (ep→ epγ) are measured at Hermes. The asymmetries arise from deeply virtual Compton scattering (DVCS) and its interference with the Bethe-Heitler process. These asymmetries provide the theoretically cleanest access to Generalized Parton Distributions. A recoil detector has been installed in HERMES that allows for the detection of all final state particles in the process ep→ epγ. It consisted of a silicon strip detector, a scintillating fibre tracker and a photon detector surrounded by a 1 T superconducting magnet.
In previous publications, associated processes ep→ eγ p π⁰ and ep→ e γ n π⁺ contributed as background processes about 12 % to the DVCS signal. The new ability of HERMES to detect the recoil particles allows to select and measure the associated processes, and it also allows to select clean DVCS processes by reducing the associated background processes to a negligible level. Recent HERMES results on azimuthal asymmetries obtained in DVCS and in the associated processes are presented.