<‘γ^*N⃗Δ transition form factors: A new analysis of data on p(e,e^′p)π⁰ at Q²=2.8 and 4.0 (GeV/c)²

Recent JLab data of the differential cross section for the reaction p(e,e^′p)π⁰ in the invariant mass region of 1.1<W<1.4 GeV at four-momentum transfer squared Q²=2.8 and 4.0 (GeV/c)² are analyzed with two models, both of which give an excellent description of most of the existing pion electroproduction data below W<1.5 GeV. We find that at up to Q²=4.0 (GeV/c)², the extracted helicity amplitudes A_3/2 and A_/2 remain comparable with each other, implying that hadronic helicity is not conserved at this range of Q². The ratios E₁₊/M₁₊ obtained show, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and to become positive with increasing Q². This is a possible indication of a very slow approach toward the pQCD region. Furthermore, we find that the bare helicity amplitude A_1/2 and S_1/2, but not A_3/2, starts exhibiting the scaling behavior at about Q²>~2.5(GeV/c)².