S. S. Kamalov

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 2GeV 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 2GeV. Because of its inherent simplicity, MAID2007 is well adopted for predictions and analysis of the observables in pion photo- and electroproduction.

Model dependence of single-energy fits to pion photoproduction data

Abstract.Model dependence of multipole analysis has been explored through energy-dependent and single-energy fits to pion photoproduction data. The MAID energy-dependent solution has been used as input for an event generator producing realistic pseudo data. These were fitted using the SAID parametrization approach to determine single-energy and energy-dependent solutions over a range of lab photon energies from 200 to 1200MeV. The resulting solutions were found to be consistent with the input amplitudes from MAID. Fits with a χ-squared per datum of unity or less were generally achieved. We discuss energy regions where consistent results are expected, and explore the sensitivity of fits to the number of included single- and double-polarization observables. The influence of Watson’s theorem is examined in detail.

Nucleon resonances in pi N scattering up to energies s**(1/2) < 2.0-GeV

A meson-exchange model for pion-nucleon scattering was previously constructed using a three-dimensional reduction scheme of the Bethe-Salpeter equation for a model Lagrangian involving \pi, \eta, N, \Delta, \rho, and \sigma fields. We thereby extend our previous work by including the \eta N channel and all the \pi N resonances with masses ~ 2 GeV, up to the F waves. The effects of the \pi\pi N channels are taken into account by introducing an effective width in the resonance propagators. The extended model gives an excellent fit to both \pi N phase shifts and inelasticity parameters in all channels up to the F waves and for energies below 2 GeV. We present a new scheme to extract the properties of overlapping resonances. The predicted values for the resonance masses and widths as well as resonance pole positions and residues are compared to the listing of the Particle Data Group.

Multipole Analysis of a Benchmark Data Set for Pion Photoproduction

We have fitted low- and medium-energy benchmark datasets employing methods used in the MAID/SAID and dynamical model analyses. Independent fits from the Mainz, RPI, Yerevan, and Kharkov groups have also been performed over the low-energy region. Results for the multipole amplitudes are compared in order to gauge the model-dependence of such fits, given identical data and a single method for error handling.

Asymmetries for elastic scattering ofπ±from polarized3He atΔresonance energies

Asymmetries A{sub y} for {pi}{sup +} and {pi}{sup {minus}} elastic scattering from polarized {sup 3}He were measured at incident energies passing through the {pi} nucleon P{sub 33}, or {Delta}(1232), resonance. The data were taken at the Clinton P. Anderson Meson Physics Facility using the high-energy pion channel P{sup 3} and a large acceptance spectrometer to detect the scattered pions. The polarized {sup 3}He target, originally developed at TRIUMF, was modified for these experiments by the addition of diode lasers. Completely unexpected negative asymmetries were observed at and below the resonance in {pi}{sup +} scattering near 50{degree}{endash}60{degree}, which cannot be reproduced by multiple scattering theory and Faddeev wave functions. A hybrid model, which adds a {Delta}-neutron spin-spin interaction term to the conventional calculations, provides a good description of the {pi}{sup +} data. For {pi}{sup {minus}} scattering this term predicts a negligible effect on A{sub y} and the data do not show the anomalous A{sub y} seen with {pi}{sup +}. {copyright} {ital 1997} {ital The American Physical Society}

(e, e′), (γ, π+ and (π−, γ) on12C and13C

A detailed theoretical analysis of spin degrees of freedom in carbon isotopes is performed, probing them by electron scattering, pion photoproduction and radiative pion capture from the mesoatomic orbits.

Spin-dipole excitations of6Li in charged pion photoproduction

In the framework of bound shell model we have calculated the photoproduction of charged pions on6Li when spin-isospin dipole resonance is excited. It is shown that the transition strength concentrates in several energy regions. Such a gross-structure of the excitation spectrum is governed by the configurational splitting of the resonance. The excitation spectrum in6Li(γ, τ)-reaction is compared with the6Li(τ, γ), (e, e′) and (n, p)-reaction spectra where spin-isospin transitions are dominating too.

Nucleon resonances inπNscattering up to energiess⩽2.0GeV

A meson-exchange model for pion-nucleon scattering was previously constructed using a three-dimensional reduction scheme of the Bethe-Salpeter equation for a model Lagrangian involving \pi, \eta, N, \Delta, \rho, and \sigma fields. We thereby extend our previous work by including the \eta N channel and all the \pi N resonances with masses ~ 2 GeV, up to the F waves. The effects of the \pi\pi N channels are taken into account by introducing an effective width in the resonance propagators. The extended model gives an excellent fit to both \pi N phase shifts and inelasticity parameters in all channels up to the F waves and for energies below 2 GeV. We present a new scheme to extract the properties of overlapping resonances. The predicted values for the resonance masses and widths as well as resonance pole positions and residues are compared to the listing of the Particle Data Group.

Multipole analysis for pion photoproduction with MAID and a dynamical models

Results of new analysis of pion photoproduction data obtained with Dynamical and MAID models are presented

Asymmetries for elastic scattering of pi+- from polarized He-3 at Delta resonance energies

Asymmetries A{sub y} for {pi}{sup +} and {pi}{sup {minus}} elastic scattering from polarized {sup 3}He were measured at incident energies passing through the {pi} nucleon P{sub 33}, or {Delta}(1232), resonance. The data were taken at the Clinton P. Anderson Meson Physics Facility using the high-energy pion channel P{sup 3} and a large acceptance spectrometer to detect the scattered pions. The polarized {sup 3}He target, originally developed at TRIUMF, was modified for these experiments by the addition of diode lasers. Completely unexpected negative asymmetries were observed at and below the resonance in {pi}{sup +} scattering near 50{degree}{endash}60{degree}, which cannot be reproduced by multiple scattering theory and Faddeev wave functions. A hybrid model, which adds a {Delta}-neutron spin-spin interaction term to the conventional calculations, provides a good description of the {pi}{sup +} data. For {pi}{sup {minus}} scattering this term predicts a negligible effect on A{sub y} and the data do not show the anomalous A{sub y} seen with {pi}{sup +}. {copyright} {ital 1997} {ital The American Physical Society}