Eur. Phys. J. A (2005) 24: 445-458
https://doi.org/10.1140/epja/i2005-10032-4

Original Article

Deeply virtual and exclusive electroproduction of ω-mesons

¹ CEA-Saclay, Service de Physique Nucléaire, F-91191, Gif-sur-Yvette, France
² Institut de Physique Nucléaire, F-91406, Orsay, France
³ Thomas Jefferson National Accelerator Facility, 23606, Newport News, VA, USA
⁴ Arizona State University, 85287-1504, Tempe, AZ, USA
⁵ University of California at Los Angeles, 90095-1547, Los Angeles, CA, USA
⁶ Carnegie Mellon University, 15213, Pittsburgh, PA, USA
⁷ Catholic University of America, 20064, Washington, DC, USA
⁸ Christopher Newport University, 23606, Newport News, VA, USA
⁹ University of Connecticut, 06269, Storrs, CT, USA
¹⁰ Edinburgh University, EH9 3JZ, Edinburgh, UK
¹¹ Florida International University, 33199, Miami, FL, USA
¹² Florida State University, 32306, Tallahassee, FL, USA
¹³ Physikalisches Institut der Universität Gießen, 35392, Gießen, Germany
¹⁴ The George Washington University, 20052, Washington, DC, USA
¹⁵ University of Glasgow, G12 8QQ, Glasgow, UK
¹⁶ Laboratori Nazionali di Frascati, INFN, Frascati (RM), Italy
¹⁷ Sezione di Genova, INFN, I-16146, Genova, Italy
¹⁸ Idaho State University, 83209, Pocatello, ID, USA
¹⁹ Institute für Strahlen und Kernphysik, Universität Bonn, Germany
²⁰ Institute of Theoretical and Experimental Physics, 117259, Moscow, Russia
²¹ James Madison University, 22807, Harrisonburg, VA, USA
²² Kyungpook National University, 702-701, Daegu, The Republic of Korea
²³ Massachusetts Institute of Technology, 02139-4307, Cambridge, MA, USA
²⁴ University of Massachusetts, 01003, Amherst, MA, USA
²⁵ General Nuclear Physics Institute, Moscow State University, 119899, Moscow, Russia
²⁶ University of New Hampshire, 03824-3568, Durham, NH, USA
²⁷ Norfolk State University, 23504, Norfolk, VA, USA
²⁸ Ohio University, 45701, Athens, OH, USA
²⁹ Old Dominion University, 23529, Norfolk, VA, USA
³⁰ University of Pittsburgh, 15260, Pittsburgh, PA, USA
³¹ Rensselaer Polytechnic Institute, 12180-3590, Troy, NY, USA
³² Rice University, 77005-1892, Houston, TX, USA
³³ University of Richmond, 23173, Richmond, VA, USA
³⁴ University of South Carolina, 29208, Columbia, SC, USA
³⁵ Union College, 12308, Schenectady, NY, USA
³⁶ Virginia Polytechnic Institute and State University, 24061-0435, Blacksburg, VA, USA
³⁷ University of Virginia, 22901, Charlottesville, VA, USA
³⁸ College of William and Mary, 23187-8795, Williamsburg, VA, USA
³⁹ Yerevan Physics Institute, 375036, Yerevan, Armenia

Received: 24 February 2005
Accepted: 21 April 2005
Published online: 8 June 2005

Abstract

The exclusive ω electroproduction off the proton was studied in a large kinematical domain above the nucleon resonance region and for the highest possible photon virtuality (Q²) with the 5.75 GeV beam at CEBAF and the CLAS spectrometer. Cross-sections were measured up to large values of the four-momentum transfer (- t < 2.7 GeV²) to the proton. The contributions of the interference terms σ_{TT} and σ_{TL} to the cross-sections, as well as an analysis of the ω spin density matrix, indicate that helicity is not conserved in this process. The t-channel π⁰ exchange, or more generally the exchange of the associated Regge trajectory, seems to dominate the reaction γ^* p↦ωp, even for Q² as large as 5 GeV². Contributions of handbag diagrams, related to Generalized Parton Distributions in the nucleon, are therefore difficult to extract for this process. Remarkably, the high-t behaviour of the cross-sections is nearly Q²-independent, which may be interpreted as a coupling of the photon to a point-like object in this kinematical limit.