142 research outputs found

    Electroexcitation of the Roper resonance in the relativistic quark models

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    The amplitudes of the transition gamma* N -> P11(1440) are calculated within light-front relativistic quark model assuming that the P11(1440) is the first radial excitation of the 3q ground state. The results are presented along with the predictions obtained in other relativistic quark models. In comparison with the previous calculations, we have extended the range of Q^2 up to 4.5 GeV^2 to cover the kinematic interval of the forthcoming experimental data. Using approach based on PCAC, we have checked the relative sign between quark model predictions for the N and P11(1440) contributions to the pion electroproduction found in previous investigations.Comment: 5 pages, 1 figure, accepted by PR

    Q^2-evolution of Delta N gamma form factors up to 4 (GeV/c)^2 from JLab data

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    We present the results on the ratios E1+(3/2)/M1+(3/2)E_{1+}^{(3/2)}/M_{1+}^{(3/2)} and S1+(3/2)/M1+(3/2)S_{1+}^{(3/2)}/M_{1+}^{(3/2)} for the γ∗N→Δ(1232)\gamma^* N \to \Delta(1232) transition at Q2≤4(GeV/c)2Q^2\leq 4 (GeV/c)^2 extracted from the p(e,e′p)π0p(e,e'p)\pi^0 cross section using two approaches: dispersion relations and modified version of unitary isobar model. The obtained results are in good agreement with the results of other analyses obtained using truncated multipole expansion at Q2=0.4, 0.525, 0.65, 0.75, 0.9, 1.15, 1.45, 1.8(GeV/c)2Q^2=0.4,~0.525,~0.65,~0.75,~0.9,~1.15,~1.45,~1.8 (GeV/c)^2 and within dynamical and unitary isobar models at Q2=2.8, 4(GeV/c)2Q^2=2.8,~4 (GeV/c)^2 . According to obtained results the ratio E1+(3/2)/M1+(3/2)E_{1+}^{(3/2)}/M_{1+}^{(3/2)} remains small in all investigated region of Q2Q^2 with very unclear tendency to cross zero above 2(GeV/c)22 (GeV/c)^2. The absolute value of the ratio S1+(3/2)/M1+(3/2)S_{1+}^{(3/2)}/M_{1+}^{(3/2)} is clearly increasing with increasing Q2Q^2, while it should be a constant value in the pQCD asymptotics. So, at Q2≤4(GeV/c)2Q^2\leq4 (GeV/c)^2 there is no evidence of approaching pQCD regime for these ratios. None of the soft approaches gives satisfactory description of the obtained results.Comment: 5 pages, 1 figure, invited talk at the Workshop on Exclusive Processes at High Momentum Transfer, May 15-18, 2002, Jefferson La
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