Eur. Phys. J. A (2017) 53: 8
https://doi.org/10.1140/epja/i2017-12194-8

Regular Article - Experimental Physics

Double-polarization observable G in neutral-pion photoproduction off the proton

¹ Helmholtz-Institut für Strahlen, und Kernphysik der Universität Bonn, Bonn, Germany
² Physikalisches Institut, Universität Bonn, Bonn, Germany
³ Petersburg Nuclear Physics Institute, Gatchina, Russia
⁴ Institut für Experimentalphysik I, Ruhr-Universität Bochum, Bochum, Germany
⁵ Institut für Physik, Universität Basel, Basel, Switzerland
⁶ Department of Physics, Florida State University, Tallahassee, FL, USA
⁷ II. Physikalisches Institut, Universität Gießen, Gießen, Germany

^* e-mail: thiel@hiskp.uni-bonn.de

Received: 13 April 2016
Accepted: 14 December 2016
Published online: 18 January 2017

Abstract

This paper reports on a measurement of the double-polarization observable G in photoproduction off the proton using the CBELSA/TAPS experiment at the ELSA accelerator in Bonn. The observable G is determined from reactions of linearly polarized photons with longitudinally polarized protons. The polarized photons are produced by bremsstrahlung off a diamond radiator of well-defined orientation. A frozen spin butanol target provides the polarized protons. The data cover the photon energy range from 617 to 1325 MeV and a wide angular range. The experimental results for G are compared to predictions by the Bonn-Gatchina (BnGa), Jülich-Bonn (JüBo), MAID and SAID partial wave analyses. Implications of the new data for the pion photoproduction multipoles are discussed.