Deeply virtual and exclusive electroproduction of ω-mesons

Christopher Newport University 23606 Newport News VA USA; University of Connecticut 06269 Storrs CT USA; Idaho State University 83209 Pocatello ID USA; Institute für Strahlen und Kernphysik Universität Bonn Germany; Union College 12308 Schenectady NY USA
European Physical Journal A (Impact Factor: 2.42). 01/2005; 24(3):445-458. DOI: 10.1140/epja/i2005-10032-4
Source: arXiv

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="">2) 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.

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