We report a new measurement of the exclusive electroproduction reaction γ+p→π0p to explore the evolution from soft nonperturbative physics to hard processes via the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the N→Δ transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c2, 4π center-of-mass solid angle, and Q2 from 3 to 6 GeV2/c2, the highest yet achieved. It is found that the magnetic form factor G+M decreases with Q2 more steeply than the proton magnetic form factor, the ratio E1+/M1+ is small and negative, indicating strong helicity nonconservation, and the ratio S1+/M1+ is negative, while its magnitude increases with Q2.
Physical Review Letters
Ungaro, M.; Biselli, Angela; and CLAS Collaboration, "Measurement of the N→Δ+(1232) Transition at High-Momentum Transfer by π0 Electroproduction" (2006). Physics Faculty Publications. 74.
M. Ungaro et al. [CLAS Collaboration], "Measurement of the N→Δ+(1232) Transition at High-Momentum Transfer by π0 Electroproduction", Physical Review Letters 97.11 (2006) DOI: 10.1103/PhysRevLett.97.112003