29 research outputs found
Nucleon polarizabilities in the perturbative chiral quark model
The nucleon polarizabilities alpha(E) and beta(M) are studied in the context
of the perturbative chiral quark model. We demonstrate that meson cloud effects
are sufficient to explain the electric polarizability of nucleon. Contributions
of excite quark states to the paramagnetic polarizability are dominant and
cancel the diamagnetic polarizability arising from the chiral field. The
obtained results are compared to data and other theoretical predictions.Comment: 25 pages, 18 figures, 2 table
Quasi-free Compton Scattering and the Polarizabilities of the Neutron
Differential cross sections for quasi-free Compton scattering from the proton
and neutron bound in the deuteron have been measured using the Glasgow/Mainz
tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48
cm 64 cm NaI(Tl) photon detector and the G\"ottingen SENECA
recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV
at . Liquid deuterium and hydrogen targets
allowed direct comparison of free and quasi-free scattering from the proton.
The neutron detection efficiency of the SENECA detector was measured via the
reaction . The "free" proton Compton scattering cross
sections extracted from the bound proton data are in reasonable agreement with
those for the free proton which gives confidence in the method to extract the
differential cross section for free scattering from quasi-free data.
Differential cross sections on the free neutron have been extracted and the
difference of the electromagnetic polarizabilities of the neutron have been
obtained to be
in units . In combination with the polarizability sum deduced from photoabsorption data, the neutron electric and
magnetic polarizabilities, and
are obtained. The backward spin polarizability of the neutron was determined to
be
Quasi-free Compton Scattering from the Deuteron and Nucleon Polarizabilities
Cross sections for quasi-free Compton scattering from the deuteron were
measured for incident energies of 236--260 MeV at the laboratory angle -135
degrees. The recoil nucleons were detected in a liquid-scintillator array
situated at 20 degrees. The measured differential cross sections were used,
with the calculations of Levchuk et al., to determine the polarizabilities of
the bound nucleons. For the bound proton, the extracted values were consistent
with the accepted value for the free proton. Combining our results for the
bound neutron with those from Rose et al., we obtain one-sigma constraints of
alpha_n = 7.6-14.0 and beta_n = 1.2-7.6.Comment: 4 pages, 3 figures, accepted in PR
Measurement of the Electric and Magnetic Polarizabilities of the Proton
The Compton scattering cross section on the proton has been measured at
laboratory angles of 90 and 135 using tagged photons in the
energy range 70--100 MeV and simultaneously using untagged photons in the range
100--148~MeV. With the aid of dispersion relations, these cross sections were
used to extract the electric and magnetic polarizabilities, and
respectively, of the proton. We find
in agreement with a model-independent dispersion sum rule, and
where the errors shown are statistical, systematic, and model-dependent,
respectively. A comparison with previous experiments is given and global values
for the polarizabilities are extracted.Comment: 35 pages, 11 PostScript figures, uses RevTex 3.
and Polarizabilities from {} Data on the Base of S-Matrix Approach
We suggest the most model-independent and simple description of the
process near threshold in framework of S-matrix
approach. The amplitudes contain the pion polarizabilities and rather
restricted information about interaction. Application of these
formulae for description of MARK-II \cite{M2} and Crystal Ball \cite{CB} data
gives: ,
(in units system ) at the experimental values of scattering lengths. Both
values are compartible with current algebra predictions.Comment: LaTeX, 14 pages plus 6 figures (not included, available upon request)
, ISU-IAP.Th93-03, Irkuts
Cluster Transformation Coefficients for Structure and Dynamics Calculations in n-Particle Systems: Atoms, Nuclei, and Quarks
The structure and dynamics of an n-particle system are described with coupled
nonlinear Heisenberg's commutator equations where the nonlinear terms are
generated by the two-body interaction that excites the reference vacuum via
particle-particle and particle-hole excitations. Nonperturbative solutions of
the system are obtained with the use of dynamic linearization approximation and
cluster transformation coefficients. The dynamic linearization approximation
converts the commutator chain into an eigenvalue problem. The cluster
coefficients factorize the matrix elements of the (n)-particles or
particle-hole systems in terms of the matrix elements of the (n-1)-systems
coupled to a particle-particle, particle-hole, and hole-hole boson. Group
properties of the particle-particle, particle-hole, and hole-hole permutation
groups simplify the calculation of these coefficients. The particle-particle
vacuum-excitations generate superconductive diagrams in the dynamics of
3-quarks systems. Applications of the model to fermionic and bosonic systems
are discussed.Comment: 13 pages, 5 figures, Wigner Proceedings for Conference Wigner
Centenial Pecs, July 8-12, 200
Neutron polarizabilities investigated by quasi-free Compton scattering from the deuteron
Measuring Compton scattered photons and recoil neutrons in coincidence,
quasi-free Compton scattering by the neutron has been investigated at MAMI
(Mainz) at in an energy range from 200 to 400 MeV.
From the data a polarizability difference of in units of has been
determined. In combination with the polarizability sum deduced from photo absorption data, the neutron electric and
magnetic polarizabilities, and ,
are obtained
Hadron Polarizabilities and Form Factors
This is the summary of the working group on Hadron Polarizabilities and Form
Factors of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997.Comment: 21 pages LaTeX2e, uses epsf, 9 fig