Eur. Phys. J. A (2007) 33: 133-146
https://doi.org/10.1140/epja/i2007-10455-9

Regular Article - Experimental Physics

Photoproduction of η -mesons off protons

¹ Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, Germany
² Physikalisches Institut, Universität Erlangen, Germany
³ Department of Physics, Florida State University, Tallahassee, FL, USA
⁴ Petersburg Nuclear Physics Institute, Gatchina, Russia
⁵ Physikalisches Institut, Universität Bonn, Germany
⁶ Kernfysisch Versneller Instituut, Groningen, The Netherlands
⁷ Institut für Experimentalphysik I, Universität Bochum, Germany
⁸ Institut für Physik, Universität Basel, Switzerland
⁹ II. Physikalisches Institut, Universität Gießen, Germany

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

Received: 5 June 2007
Accepted: 22 July 2007
Published online: 24 August 2007

Abstract

Photoproduction of η -mesons was studied with the Crystal-Barrel detector at ELSA for photon energies in the range from 0.75 to 3GeV. Total and differential cross-sections are presented. The η mesons are detected in two decay modes, in η → 2γ and in η → 3π⁰ → 6γ . The cross-sections vary slowly as functions of energy and η production angle suggesting that only few resonances make significant contributions to the cross-section. For photon energies above 1.5GeV, the differential cross-sections show a strong forward peak due to meson exchanges in the t channel. A comparison of the η -photoproduction cross-sections with SAID and MAID as well as with a partial-wave analysis performed on our data in combination with other data sets shows good agreement. The Bonn-Gatchina partial-wave analysis suggests that the largest contribution to η photoproduction for energies below 3GeV proceeds via three resonances, the well-known N(1535)S ₁₁ , via N(1720)P ₁₃ , and a newly suggested N(2070)D ₁₅ .