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Ungaro, M.; University of Connecticut, Storrs, Connecticut 06269; Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606; Stoler, P.; Adams, G.; Cummings, J. P.; Kubarovsky, V.; Li Ji; Napolitano, J.; Aznauryan, I.; Yerevan Physics Institute, 375036 Yerevan; Burkert, V. D.; Avakian, H.; Brooks, W. K.; Cords, D.; Degtyarenko, P. V.; Deur, A.; Elouadrhiri, L.; Guo, L.; Gyurjyan, V.; Heddle, D.; Ito, M. M.; Laget, J. M.
Physical review letters, 09/2006, Volume: 97, Issue: 11Journal Article
We report a new measurement of the exclusive electroproduction reaction {gamma}*p{yields}{pi}{sup 0}p to explore the evolution from soft nonperturbative physics to hard processes via the Q{sup 2} dependence of the magnetic (M{sub 1+}), electric (E{sub 1+}), and scalar (S{sub 1+}) multipoles in the N{yields}{delta} transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c{sup 2}, 4{pi} center-of-mass solid angle, and Q{sup 2} from 3 to 6 GeV{sup 2}/c{sup 2}, the highest yet achieved. It is found that the magnetic form factor G{sub M}* decreases with Q{sup 2} more steeply than the proton magnetic form factor, the ratio E{sub 1+}/M{sub 1+} is small and negative, indicating strong helicity nonconservation, and the ratio S{sub 1+}/M{sub 1+} is negative, while its magnitude increases with Q{sup 2}.
