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HK: Fachverband Physik der Hadronen und Kerne

HK 2: Elektromagnetische und Hadronische Sonden

HK 2.1: Group Report

Monday, March 10, 2008, 14:00–14:30, 1C

Latest results from the GDH-experiment on the deuteron — •Mauricio Martinez for the A2 collaboration — Institut für Kernphysik, Universität Mainz

Already in 1965 the Gerasimov-Drell-Hearn (GDH) sum rule, connecting the helicity dependent photoabsorption cross sections with the anomalous magnetic moment of the nucleon, was derived theoretically.

Some years ago the GDH collaboration has started an extended program at the electron accelerators MAMI in Mainz and ELSA in Bonn to measure the photoabsorption cross sections of circularly polarized photons on longitudinally polarized nucleons to determine for the first time a double polarization observable in a large kinematical range, which will provide new information about the helicity dependent excitation spectrum of the nucleon via an enhancement of small multipole amplitudes in interference terms.

The experiment has been performed using the polarized electron beam of the Mainz accelerator MAMI in the energy range 140 - 800 MeV and at the Bonn accelerator ELSA up to an energy of approximately 3 GeV. Our apparatus consisted of the Bonn frozen spin polarized target (proton and deuteron) with high angular acceptance which had been integrated into a 4 π-detector. The polarization of the photon beam was monitored using a moeller polarimeter, the target polarization was measured by a NMR system.

In this talk our recent data from the deuteron run in 2003 will be discussed.