Measurement of the E 2 / M 1 Ratio in the N → Δ Transition using the reaction p ( γ → , p ) π o

The small electric quadrupole $E2$ amplitude of the predominantly magnetic dipole $M1$ $p\\ensuremath{\\rightarrow}\\ensuremath{\\Delta}(1232)$ transition has been measured using 270 to 420 MeV tagged linearly polarized photons in the $p(\\stackrel{\\ensuremath{\\rightarrow}}{\\ensuremath{\\gamma}},p){\\ensuremath{\\pi}}^{o}$ reaction at the Mainz Microtron MAMI. Differential cross sections and photon asymmetries were determined by measuring the recoil proton in the cylindrically symmetric $4\\ensuremath{\\pi}$ detector DAPHNE. From the proton angular distributions the ratio $E2/M1\\phantom{\\rule{0ex}{0ex}}=\\phantom{\\rule{0ex}{0ex}}\\ensuremath{-}(2.5\\ifmmode\\pm\\else\\textpm\\fi{}0.2\\ifmmode\\pm\\else\\textpm\\fi{}0.2)%$ at the maximum of the $\\ensuremath{\\Delta}(1232)$ resonance has been derived.