Eur. Phys. J. A (2010) 43: 261-267
https://doi.org/10.1140/epja/i2010-10918-x

Regular Article - Experimental Physics

Evidence for a backward peak in the γd → π⁰d cross section near the η threshold

¹ The George Washington University, 20052, Washington, DC, USA
² Institute of Theoretical and Experimental Physics, 117259, Moscow, Russia
³ Argonne National Laboratory, 60439, Argonne, IL, USA
⁴ Arizona State University, 85287, Tempe, AZ, USA
⁵ University of California at Los Angeles, 90095, Los Angeles, CA, USA
⁶ California State University, 90747, Dominguez Hills, Carson, CA, USA
⁷ Carnegie Mellon University, 15213, Pittsburgh, PA, USA
⁸ Catholic University of America, 20064, Washington, DC, USA
⁹ Service de Physique Nucléaire, CEA-Saclay, F91191, Gif-sur-Yvette, France
¹⁰ Christopher Newport University, 23606, Newport News, VA, USA
¹¹ University of Connecticut, 06269, Storrs, CT, USA
¹² Edinburgh University, EH9 3JZ, Edinburgh, UK
¹³ Fairfield University, 06824, Fairfield, CT, USA
¹⁴ Florida International University, 33199, Miami, FL, USA
¹⁵ Florida State University, 32306, Tallahassee, FL, USA
¹⁶ University of Glasgow, G12 8QQ, Glasgow, UK
¹⁷ Idaho State University, 83209, Pocatello, ID, USA
¹⁸ Laboratori Nazionali di Frascati, INFN, 00044, Frascati, Italy
¹⁹ INFN, Sezione di Genova, 16146, Genova, Italy
²⁰ Institut de Physique Nucleaire ORSAY, Orsay, France
²¹ James Madison University, 22807, Harrisonburg, VA, USA
²² Kyungpook National University, 702-701, Daegu, Republic of Korea
²³ University of Massachusetts, 01003, Amherst, MA, USA
²⁴ General Nuclear Physics Institute, Moscow State University, 119899, Moscow, Russia
²⁵ University of New Hampshire, 03824, Durham, NH, USA
²⁶ Norfolk State University, 23504, Norfolk, VA, USA
²⁷ Ohio University, 45701, Athens, OH, USA
²⁸ Old Dominion University, 23529, Norfolk, VA, USA
²⁹ Rensselaer Polytechnic Institute, 12180, Troy, NY, USA
³⁰ Rice University, 77005, Houston, TX, USA
³¹ University of Richmond, 23173, Richmond, VA, USA
³² University of South Carolina, 29208, Columbia, SC, USA
³³ Thomas Jefferson National Accelerator Facility, 23606, Newport News, VA, USA
³⁴ TRIUMF, V6T 2A3, Vancouver, Canada
³⁵ Union College, 12308, Schenectady, NY, USA
³⁶ Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA
³⁷ University of Virginia, 22901, Charlottesville, VA, USA
³⁸ College of William and Mary, 23187, Williamsburg, VA, USA
³⁹ Yerevan Physics Institute, 375036, Yerevan, Armenia
⁴⁰ INRNE, BAS, Sofia, Bulgaria

^* e-mail: ilieva@sc.edu

Received: 6 October 2009
Revised: 18 December 2009
Published online: 3 February 2010

Abstract

High-quality cross sections for the reaction γd → π⁰ d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the η-meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near E _γ = 700 MeV. Our model analysis shows that it can be explained by η excitation in the intermediate state. The effect is the result of the contribution of the N(1535)S ₁₁-resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the excitation of an intermediate η-meson dominates.