Unitary isobar model --MAID2007

Abstract

The unitary isobar model MAID2007 has been developed to analyze the world data of pion photo-and electroproduction. The model contains both a common background and several resonance terms. The background is unitarized according to the K-matrix prescription, and the 13 four-star resonances with masses below 2 GeV are described by appropriately unitarized Breit-Wigner forms. The data have been analyzed by both single-energy and global fits, and the transverse and longitudinal helicity amplitudes have been extracted for the four-star resonances below 2 GeV. Because of its inherent simplicity, MAID2007 is well adopted for predictions and analysis of the observables in pion photo-and electroproduction.

Polarised Photon Beams for the BGO-OD Experiment at ELSA

“…5(a)-5(c), the extracted beam asymmetry is plotted against the centre of mass polar angle in one energy bin for pπ 0 , and two energy bins for pη. Within the limited statistical accuracy, the data is consistent with the world data, represented here by the MAID PWA solution [5]. Higher statistics over a much greater kinematic range is expected soon in the PhD thesis of Andreas Bella [6].…”

Baryons as relativistic three-quark bound states

“…3.6. [29] and the curves are the MAID parametrizations [30]. The triangles at the real photon point are the PDG values [9].…”

“…The multipole amplitudes are linear combinations of the transverse partial wave helicity amplitudes, which at the resonance locations are related to the N γ * → N * helicity amplitudes (see e.g. [11,13,30] for the explicit formulas).…”

Pion Production in Wroclaw Neutrino Event Generator and its Comparison with Other Generators

“…Vector properties of baryons are coming directly from the MAID analysis [7], whereas their axial excitation current is modeled using a dipole form factor with axial coupling strength following the off-diagonal Goldberger-Treiman relation [23]. The only exception is the better understood ∆(1232) resonance with axial form factors fitted to ANL/BNL data.…”

“…Here the RES process is chosen to be the main example. In MC generators resonant pion production is either based upon the Rein-Sehgal paper [5] (continuation of the earlier quark Feynman-Kislinger-Ravndal model [6]) or on a variety of isobar models (see e. g. [7]). Another group of more sophisticated models (see e. g. [8], [9], [10], [11], [12], [13]) is still waiting to be implemented in MC generators.…”