Evaluation of multipoles for photo- and electroproduction of pions

Schwela, D.; Weizel, Rainer

doi:10.1007/bf01392064

Cited by 51 publications

(27 citation statements)

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“…At the moment, however, we obtain an excellent representation of the analysed data by use of the method of Ref. [3]. Therefore we deem it worthwhile extending this method to the second resonance region as a next step.…”

Section: Introductionmentioning

confidence: 91%

Multipole analysis of pion photoproduction based on fixed t dispersion relations and unitarity

1998

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We h a v e analysed pion photoproduction imposing constraints from xed t dispersion relations and unitarity. Coupled integral equations for the S and P wave m ultipoles were derived from the dispersion relations and solved by the method of Omnes and Muskhelishvili. The free parameters were determined by a t to the most recent data for + and 0 production on the proton as well as production on the neutron, in the energy range 160 MeV E 420 MeV. The lack of high precision data on the neutron and of polarization observables leads to some limitations of our results. Especially the multipole M1 connected with the Roper resonance P11(1440) cannot be determined to the required precision. Our predictions for the threshold amplitudes are in good agreement with both the data and chiral perturbation theory. In the region of the (1232) we h a v e determined the ratio of electric quadrupole and magnetic dipole excitation. The position of the resonance pole is obtained in excellent agreement with pion-nucleon scattering, and the complex residues of the multipoles are determined with the speed-plot technique.

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Section: Introductionmentioning

confidence: 91%

Multipole analysis of pion photoproduction based on fixed t dispersion relations and unitarity

1998

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“…In this region ψ = δ πN with very good accuracy. At the higher energies, where the ∆ contribution becomes small, we will use the ansatz [23] …”

Section: Resonance Contributions -Real Photonsmentioning

confidence: 99%

A unitary isobar model for pion photo- and electroproduction on the proton up to 1 GeV

et al. 1999

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A new operator for pion photo-and electroproduction has been developed for nuclear applications at photon equivalent energies up to 1 GeV. The model contains Born terms, vector mesons and nucleon resonances (P33(1232), P11(1440), D13(1520), S11(1535), F15(1680), and D33 (1700)). The resonance contributions are included taking into account unitarity to provide the correct phases of the pion photoproduction multipoles. The Q 2 dependence of electromagnetic resonance vertices is described with appropriate form factors in the electromagnetic helicity amplitudes. Within this model we have obtained good agreement with the experimental data for pion photo-and electroproduction on the nucleon for both differential cross sections and polarization observables. The model can be used as a starting point to predict and analyze forthcoming data.

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“…We have essentially followed the method of Schwela et al [15,16] to solve Eq. (3) with the constraint (4).…”

Section: Pion Photoproductionmentioning

confidence: 99%

The E2/M1 and C2/M1 ratios and form factors in N→Δ transitions

Tiator¹,

Drechsel²,

Hanstein³

et al. 2001

Nuclear Physics A

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A partial wave analysis of pion photoproduction has been obtained in the framework of fixed-t dispersion relations valid from threshold up to 500 MeV . In the resonance region we have precisely determined the electromagnetic properties of the ∆(1232) resonance, in particular the E2/M1 ratio R EM = (−2.5 ± 0.1)%. For pion electroproduction recent experimental data from Mainz, Bates and JLab for Q 2 up to 4.0 (GeV/c) 2 have been analyzed with two different models, an isobar model (MAID) and a dynamical model. The E2/M1 ratios extracted with these two models show, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and become positive with increasing Q 2 . This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as R SM (0) = (−6.5 ± 0.5)%. At high Q 2 the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached.

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Evaluation of multipoles for photo- and electroproduction of pions

Cited by 51 publications

References 0 publications

Multipole analysis of pion photoproduction based on fixed t dispersion relations and unitarity

Multipole analysis of pion photoproduction based on fixed t dispersion relations and unitarity

A unitary isobar model for pion photo- and electroproduction on the proton up to 1 GeV

The E2/M1 and C2/M1 ratios and form factors in N→Δ transitions

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