Measurement of the Beam-Helicity Asymmetry in the p(e-->,e'p)π0 Reaction at the Energy of the Δ(1232) Resonance

In a p(e-->,e'p)π⁰ out-of-plane coincidence experiment at the three-spectrometer setup of the Mainz Microtron MAMI, the beam-helicity asymmetry has been precisely measured around the energy of the Δ(1232) resonance and Q² = 0.2(GeV/c)². The results are in disagreement with three up-to-date model calculations. This is interpreted as a lack of understanding of the nonresonant background, which in dynamical models is related to the pion cloud.