Effective-Lagrangian approach to the theory of pion photoproduction in theΔ(1232)region

Abstract

We investigate theoretical uncertainties and model dependence in the extraction of the nucleon-A(1232) electromagnetic transition amplitudes from the multipole data base. Our starting point is an effective Lagrangian incorporating chiral symmetry, which includes, at the tree level, the pseudovector nucleon Born terms, leading t-channel vector-meson exchanges, and s-and u-channel A exchanges. We express the nucleon-A transition magnetic dipole (MI) and electric quadrupole (E2) amplitudes in terms of two independent gauge couplings at the yNA vertex, and fit these to various multipole data sets. We find a large sensitivity to the method used in unitarizing the amplitude, and extract the E2/M1 ratio (EMR) to be negative, with a magnitude of around 1.5%. The resonant amplitudes in this work are of interest to the test of topical hadron models inspired by QCD: the sign of the EMR, extracted by us, is in accord with that predicted by most realistic models, and its magnitude lies between the predictions of the quark shell model and the Skyrmion model. Finally, our work provides a phenomenologically satisfying unitary amplitude for pion photoproduction off nucleons, which can be used as a realistic starting point for theoretical studies of this process in complex nuclei.

pp→pK+Λreaction in an effective Lagrangian model

“…For the spin-1/2 resonance the N * N π decay width, with the PS coupling, is given by 27) while that with the corresponding PV coupling is…”

“…In this paper, we investigate the associated K + production in the proton-proton collisions in the framework of an effective Lagrangian approach [25][26][27][28][29], following and extending our previous study [30,31] on π 0 and π + production. Initial interaction between two incoming nucleons is modeled by an effective Lagrangian which is based on the exchange of the π, ρ, ω and σ mesons.…”

<‘γ*N→Δtransition form factors: A new analysis of data onKamalov1, Yang2, Drechsel3 et al. 2001Phys. Rev. C14831401View full textAdd to dashboardCite

“…The first one, which is model and energy independent, consisted of making approximate multipole fits to angular distributions independently at each W , assuming M 1+ dominance, and only S and P wave contributions [7]. Another extraction of the resonance amplitudes was performed using the effective Lagrangian method [8]. In this model-dependent analysis, the resonant multipoles are expressed as a sum of background and resonance amplitudes, both prescribed by an effective Lagrangian, and unitarized with the K-matrix method.…”

Quantum corrections to baryon properties in chiral soliton models

“…Because the extraction of the electromagnetic ratio from experimental data is far from being trivial [89][90], a complete calculation of the γN → πN reaction, which includes the background with the ∆ resonance lying in the continuum would be desirable in order to obtain complex helicity amplitudes for the N∆ transition. Although such a calculation should in principle be feasible within soliton models, the effort would be tremendeous.…”