Entwicklung polarisierter Targets zur Messung der Gerasimov-Drell-Hearn-Summenregel an ELSA

Abstract

The Gerasimov-Drell-Hearn sum rule (GDH) relates the difference of the total absorption cross section of circularly polarized photons on parallelly and antiparallelly polarized nucleons to their well known quantities mass and anomalous magnetic moment. For the experimental examination of the sum rule experiments were performed in two different configurations: From the pion threshold up to a photon energy of 800 MeV data have been taken at the Mainzer Microtron (MAMI). At the Electron Stretcher Accelerator (ELSA) the measurement covered a photon energy range up to 2.9 GeV. The polarized target is an essential part of the experiment. During the data taking the target was run in the frozen spin mode to minimize the absorption of the ejected particles. In order to match the required detector geometry for full acceptance a new horizontal dilution refrigerator with an internal holding magnet was developed and used. This allowed to measure the spin dependent total photo absorption cross section difference for the first time.