Scale of corrections to the t-channel pole approximation in quasielastic pion knockout from a nucleon by high-energy electrons |
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Authors: | V G Neudatchin L L Sviridova N P Yudin |
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Institution: | (1) Institute of Nuclear Physics, Moscow State University, Vorob’evy gory, Moscow, 119899, Russia |
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Abstract: | An investigation of a dominant role of the simplest t-channel pole diagrams in pion electroproduction on nucleons for quasielastic-knockout kinematics at an electron energy of a few GeV is completed-namely, the competition between the t-channel pion and rho-meson pole amplitudes, on one hand, and the s-channel pole amplitude (tree diagram), on the other hand, is considered. When the virtual-photon mass is sufficiently large Q 2>2(GeV/c)2], the last amplitude does not make significant contributions to relevant cross sections, either the longitudinal (dσ L/dt) or the transverse (dσ T/dt) one. At Q 2=0.7(GeV/c)2, the term associated with the interference between the t-channel pion-pole amplitude and the s-channel pole amplitude is still noticeable in the longitudinal cross section. The vertex functions g ρ NN(t) as obtained from the cross section for the quasielastic knockout of rho mesons and from the cross section for pion photoproduction are compared. Their disagreement must give impetus to a further development of the gauge-invariant theory of pion photoproduction. |
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