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
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.
PACS: 13.60.Le Meson production – / 12.40.Nn Regge theory, duality, absorptive/optical models – / 12.38.Bx Perturbative calculations –
© Società Italiana di Fisica and Springer-Verlag, 2005