1,125 research outputs found
Multipole Extraction: A novel, model independent method
A novel method for extracting multipole amplitudes in the nucleon resonance
region from electroproduction data is presented. The method is based on
statistical concepts and it relies heavily on Monte Carlo and simulation
techniques; it produces precise identification and determination of the
contributing multipole amplitudes in the resonance region and for the first
time a rigorous determination of the associated experimental uncertainty. The
results are demonstrated to be independent of any model bias. The method is
applied in the reanalysis of the Bates and Mainz data.Comment: Proceedings, "Shape of Hadrons" Workshop, 27-29 April 2006, Athens,
GREEC
On hadron deformation: a model independent extraction of EMR from pion photoproduction data
The multipole content of pion photoproduction at the
resonance has been extracted from a data set dominated by recent Mainz
Microtron (MAMI) precision measurements. The analysis has been carried out in
the Athens Model Independent Analysis Scheme (AMIAS), thus eliminating any
model bias. The benchmark quantity for nucleon deformation, , was determined to be ,
thus reconfirming in a model independent way that the conjecture of baryon
deformation is valid. The derived multipole amplitudes provide stringent
constraints on QCD simulations and QCD inspired models striving to describe
hadronic structure. They are in good agreement with phenomenological models
which explicitly incorporate pionic degrees of freedom and with lattice QCD
calculations.Comment: 14 pages, 9 figures, 2 table
Energy Dependence of the Delta Resonance: Chiral Dynamics in Action
There is an important connection between the low energy theorems of QCD and
the energy dependence of the Delta resonance in pi-N scattering, as well as the
closely related gamma^{*} N -> pi N reaction. The resonance shape is due not
only to the strong pi-N interaction in the p wave but the small interaction in
the s wave; the latter is due to spontaneous chiral symmetry breaking in QCD
(i.e. the Nambu-Goldstone nature of the pion). A brief overview of experimental
tests of chiral perturbation theory and chiral based models is presentedComment: 11 pages, 6 figures, Festschrift for S.N. yan
Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at Low Q2 Using the VCS Reaction
The mean square polarizability radii of the proton have been measured for the
first time in a virtual Compton scattering experiment performed at the
MIT-Bates out-of-plane scattering facility. Response functions and
polarizabilities obtained from a dispersion analysis of the data at Q2=0.06
GeV2/c2 are in agreement with O(p3) heavy baryon chiral perturbation theory.
The data support the dominance of mesonic effects in the polarizabilities, and
the increase of beta with increasing Q2 is evidence for the cancellation of
long-range diamagnetism by short-range paramagnetism from the pion cloud
Refractive elastic scattering of carbon and oxygen nuclei: The mean field analysis and Airy structures
The experimental data on the OC and OC elastic
scatterings and their optical model analysis are presented. Detailed and
complete elastic angular distributions have been measured at the Strasbourg
Vivitron accelerator at several energies covering the energy range between 5
and 10 MeV per nucleon. The elastic scattering angular distributions show the
usual diffraction pattern and also, at larger angles, refractive effects in the
form of nuclear rainbow and associated Airy structures. The optical model
analysis unambiguously shows the evolution of the refractive scattering
pattern. The observed structure, namely the Airy minima, can be consistently
described by a nucleus-nucleus potential with a deep real part and a weakly
absorptive imaginary part. The difference in absorption in the two systems is
explained by an increased imaginary (mostly surface) part of the potential in
the OC system. The relation between the obtained potentials and
those reported for the symmetrical OO and CC
systems is drawn.Comment: 10 pages, 9 figures, Phys. rev. C in pres
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