gamma*N ->Delta transition form factors: A new analysis of data on p (e,e ' p) pi(0) at Q(2)=2.8 and 4.0 (GeV/c)(2) - art. no. 032201

Recent JLab data of the differential cross section for the reaction p(e,e'p )pi (o) in the invariant mass region of 1.1<W<1.4 GeV at four-momentum tran sfer squared Q(2)=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 electr oproduction data below W< 1.5 GeV. We find that at Up to Q(2)=4.0 (GeV/c)(2 ), the extracted helicity amplitudes A(3/2) and A(/2) remain comparable wit h each other, implying that hadronic helicity is not conserved at this rang e of Q(2). The ratios E1+/M1+ obtained show, starting from a small and nega tive 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 ver y 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 Q(2)<greater than or equal to>2.5(GeV/c)(2).