E1+/M1+ and S1+/M1+ from an analysis of p(e,e'p) pi 0 in the region of the Delta (1232) resonance at Q2=3.2(GeV/c)2.

Abstract

We have analyzed exclusive $p(e, {e}^{\ensuremath{'}}p){\ensuremath{\pi}}^{0}$ data to determine the electromagnetic and scalar transition multipoles in the mass region of the $\ensuremath{\Delta}(1232)$ at the highest ${Q}^{2}$ value where data exist. The ratio of the electric quadrupole and the magnetic dipole transition moments is determined to be $\frac{{E}_{1+}}{{M}_{1+}}=0.06\ifmmode\pm\else\textpm\fi{}0.02\ifmmode\pm\else\textpm\fi{}0.03$, and for the scalar quadrupole transition we find $\frac{{S}_{1+}}{{M}_{1+}}=0.07\ifmmode\pm\else\textpm\fi{}0.02\ifmmode\pm\else\textpm\fi{}0.03$. The results rule out that perturbative QCD governs the dynamics of the ${\ensuremath{\gamma}}_{v}p\ensuremath{\Delta}$ transition at such ${Q}^{2}$. They are more consistent with predictions of relativistic extensions of the nonrelativistic constituent quark model.