Electroexcitation of theP33(1232),P11(1440

Abstract

Using two approaches-dispersion relations and the isobar model-we have analyzed recent high precision CLAS data on cross sections of π 0 , π + , and η electroproduction on protons, and the longitudinally polarized electron beam asymmetry for p( e, e p)π 0 and p( e, e n)π + . The contributions of the resonances P 33 (1232), P 11 (1440), D 13 (1520), and S 11 (1535) to π electroproduction and of S 11 (1535) to η electroproduction are found. The results obtained using the two approaches are in good agreement. There is also good agreement between amplitudes of the γ * N → S 11 (1535) transition found in π and η electroproduction. For the first time accurate results are obtained for the longitudinal amplitudes of the P 11 (1440), D 13 (1520), and S 11 (1535) electroexcitations on protons. A strong longitudinal response is found for the Roper resonance, which rules out presentation of this resonance as a hybrid state.

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

“…The approaches we use to analyze the data, DR and UIM, were successfully employed in analyses of pion photoproduction and low-Q 2 electroproduction data, see Refs. [40][41][42]. In Sec.…”

Recoil Polarization and Beam-Recoil Double Polarization Measurement ofηElectroproduction on the Proton in the Region of theS11(1535)Resonance

“…Most authors interpret this fact with a reaction mechanism dominated by the S 11 (1535) resonance. Phenomenological isobar models [11,12,13,14] can successfully describe the data with a standard Breit-Wigner shape of the contributing resonances, although dividing out the phase space reveals a relatively flat energy dependence of the s-wave amplitude at threshold.…”

“…On the theory side calculations of η photoproduction have been performed in isobar models [11,12,13,14], in the quark model [21], with dispersion relations [22], with coupled channels [23], and also a partial-wave analysis [24] has been performed. With the increasing database of high-quality data the analyses became more reliable and most of the data are very well described.…”

“…So far such unitary approaches [25,26] could successfully describe the S 11 partial wave even without a nucleon isobar by chiral dynamics with coupled channels. However, the interference with other channels such as D 13 has not yet been studied in this framework.…”

“…A first estimate of the longitudinal excitation of the S 11 (1535) resonance was extracted from pion production [13]. A value of 20% of the transverse amplitude was given in this reference, an isolated variation of S 0+ to this value would change the Eta-MAID prediction e.g.…”