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Electroproduction of the Δ ( 1232 ) Resonance at High Momentum Transfer

1999; American Physical Society; Volume: 82; Issue: 1 Linguagem: Inglês

10.1103/physrevlett.82.45

1092-0145

V. Frolov, G. S. Adams, A. Ahmidouch, Christopher Armstrong, K. Assamagan, S. Avery, O. K. Baker, P. Bosted, V. D. Burkert, R. Carlini, R. Davidson, J. Dunne, T. Eden, R. Ent, D. Gaskell, P. Guèye, W. Hinton, C. Keppel, W. Kim, M. Klusman, D. Koltenuk, D. Mack, R. Madey, D. Meekins, R. Minehart, Jason W. Mitchell, H. Mkrtchyan, Nimai C. Mukhopadhyay, J. Napolitano, G. Niculescu, I. Niculescu, M. Nozar, J. W. Price, P. Stoler, V. Tadevosian, L. Tang, M. Witkowski, S. A. Wood,

High-Energy Particle Collisions Research

We studied the electroproduction of the $\ensuremath{\Delta}(1232)$ resonance via the reaction $p({e,e}^{\ensuremath{'}}p){\ensuremath{\pi}}^{0}$ at four-momentum transfers ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.8\mathrm{and}4.0{\mathrm{GeV}}^{2}$. This is the highest ${Q}^{2}$ for which exclusive resonance electroproduction has ever been observed. Decay angular distributions for $\ensuremath{\Delta}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0}$ were measured over a wide range of barycentric energies covering the resonance. The $N--\ensuremath{\Delta}$ transition form factor ${G}_{M}^{*}$ and ratios of resonant multipoles ${E}_{1+}/{M}_{1+}$ and ${S}_{1+}/{M}_{1+}$ were extracted from the decay angular distributions. These ratios remain small, indicating that perturbative QCD is not applicable for this reaction at these momentum transfers.