Eta-photoproduction from plarized protons at ELSA

Abstract

Advances in the field of polarized solid targets allow new and improved experiments with tagged photon beams at the new cw-electron machines. At the stretcher accelearator ELSA in Bonn the first measurement of the target asymmetry for the η-photoproduction reaction γ p → η p at threshol has been performed. The frozen spin target, operated with the new technique of the so-called superconducting internal holding coils, achieved maximum proton polarizations of 85 % at 2.5 T with butanol as target material. The reaction is identified by detecting the decay photons in the neutral meson detector SPES0-2π, while the recoil protons four momenta are determined in the large angle scintillator detector PHOENICS. The results for η-photoproduction extend the existing data to polarization observables.