37 research outputs found
Towards a model-independent partial wave analysis for pseudoscalar meson photoproduction
Amplitude and partial wave analyses for pion, eta or kaon photoproduction are
discussed in the context of `complete experiments'. It is shown that the
model-independent helicity amplitudes obtained from at least 8 polarization
observables including beam, target and recoil polarization can not be used to
determine underlying resonance parameters. However, a truncated partial wave
analysis, which theoretically requires only 5 observables will be possible with
minimal model input.Comment: Proc. of NSTAR2011, 6 pages, 1 figur
Helicity Amplitudes and Sum Rules for Real and Virtual Photons
Results of the recently developed unitary isobar model (MAID) are presented
for helicity amplitudes, spin asymmetries, structure functions and relevant sum
rules for real and virtual photons in the resonance region. Our evaluation of
the energy-weighted integrals is in good agreement for the proton but shows big
discrepancies for the neutron.Comment: 10 pages LaTeX including 3 figures, Talk given at the GDH 2000
Conference, Mainz, June 14-17, 2000; to be published in World Scientifi
Electromagnetic properties of baryon resonances
Longitudinal and transverse transition form factors for most of the four-star
nucleon resonances have been obtained from high-quality cross section data and
polarization observables measured at MAMI, ELSA, BATES, GRAAL and CEBAF. As an
application, we further show how the transition form factors can be used to
obtain empirical transverse charge densities. Contour plots of the thus derived
densities are shown and compared for the Roper and S11 nucleon resonances.Comment: 5 pages, 3 figures, Proceedings of CIPANP 201
Photoproduction of eta and etaprime mesons on the nucleon
The isobar models eta-MAID and eta'-MAID have been used to analyze new data
on quasi-free eta photoproduction on the deuteron from Bonn and recent eta'
data on the proton from Jlab. In eta photoproduction on the neutron a bump
around W=1700 MeV was observed which could possibly arise from a narrow P11
state that is discussed as a non-strange member of the Theta^+ anti-decuplett.
In eta' photoproduction on the proton resonance contributions are found that
can be attributed to missing resonances in the energy region around W=1900 MeV.Comment: 9 pages, 4 figures, Workshop Meson2006, Cracow, Poland, 200
MAID Analysis Techniques
MAID is a unitary isobar model for a partial wave analysis of pion photo- and
electroproduction in the resonance region. It is fitted to the world data and
can give predictions for multipoles, amplitudes, cross sections and
polarization observables in the energy range from pion threshold up to W=2 GeV
and photon virtualities Q^2 < 5 GeV^2. Using more recent experimental results
from Mainz, Bates, Bonn and JLab for Q^2 up to 4.0 GeV^2, the Q^2 dependence of
the helicity couplings A_{1/2}, A_{3/2}, S_{1/2} has been extracted for a
series of four star resonances. We compare single-Q^2 analyses with a
superglobal fit in a new parametrization of Maid2005. Besides the (pion) MAID,
at Mainz we maintain a collection of online programs for partial wave analysis
of eta, eta' and kaon photo- and electroproduction which are all based on
similar footings with field theoretical background and baryon excitations in
Breit-Wigner form.Comment: 10 pages, 3 figurs, 2 tables, Proc. of NSTAR2005, Tallahassee, FL,
US
Generalization of the model-independent Laurent-Pietarinen single-channel pole-extraction formalism to multiple channels
A method to extract resonance pole information from single-channel
partial-wave amplitudes based on a Laurent (Mittag-Leffler) expansion and
conformal mapping techniques has recently been developed. This method has been
applied to a number of reactions and provides a model-independent extraction
procedure which is particularly useful in cases where a set of amplitudes is
available only at descrete energies. This method has been generalized and
applied to the case of a multi-channel fit, where several sets of amplitudes
are analysed simultaneously. The importance of unitarity constraints is
discussed. The final result provides a powerful, model-independent tool for
analyzing partial-wave amplitudes of coupled or connected channels based
entirely on the concepts of analyticity and unitarity