Measurement of the polarization degree of accelerated polarized electrons at the 2.5 GeV synchrotron in Bonn for energies between 0.85 and 2 GeV

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Experimental check of the Gerasimov-Drell-Hearn sum rule for ¹H

For the first time we checked the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the proton experimentally in the photon energy range from 0.2–2.9 GeV with the tagged photon facilities at MAMI (Mainz) and ELSA (Bonn). New data of the doubly polarized total cross section difference are presented in the energy range from 1.6 to 2.9 GeV. The contribution to the GDH integral from 0.2–2.9 GeV yields [254±5(stat)±12(syst)]  μb with negative contributions in the Regge regime at photon energies above 2.1 GeV. This trend supports the validity of the GDH sum rule

First measurement of the Gerasimov-Drell-Hearn sum rule for ¹H from 0.7 to 1.8 GeV at ELSA

To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68–1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4π detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9±2.4(stat)±2.2(syst)]   μb