185 research outputs found
Photoproduction of the Etas near Threshold
We extract a parameter , a characteristic product of the strong and
electromagnetic amplitudes for the N^*(1535), to be (2.20+-0.15) in unit of
10^(-4)MeV^(-1) from the new data on photoproduction of etas off proton.Comment: will be published in Phys. Rev. Let
Extraction of the Ratio of the N^*(1535) Electromagnetic Helicity Amplitudes from Eta Photoproduction off Neutrons and Protons
Using the recent precise measurements of eta photopro- duction in proton and
deuteron targets, we extract the ratio of the helicity amplitudes A^n_1/2 /
A^p_1/2, for the excitation of N^*(1535), in the effective Lagrangian approach,
It is fairly model-independent, free from the final-state interaction effects,
and negative as predicted by the quark models. We stress the importance of
polarization observables in further elucidation of the N^*(1520)
photoexcitation amplitudes.Comment: 4 figures. It will be published in Phys. Lett.
Electromagnetic Couplings of Nucleon Resonances
An effective Lagrangian calculation of pion photoproduction including all
nucleon resonances up to GeV is presented. We compare our
results to recent calculations and show the influence of different width
parametrizations and offshell cutoffs on the photoproduction multipoles. We
determine the electromagnetic couplings of the resonances from a new fit to the
multipole data.Comment: 20 pages, latex, 6 figures. Misprints corrected, text & 3 figures
adde
Photo- and electroproduction of the eta and eta-prime mesons
We discuss the eta and eta prime photo- and electroproduction as a way to
probe the nucleon resonance structure.Comment: 6 pages,including 2 figs.(psfig
Hoelder Inequalities and QCD Sum-Rule Bounds on the Masses of Light Quarks
QCD Laplace Sum-Rules must satisfy a fundamental Hoelder inequality if they
are to consistently represent an integrated hadronic spectral function. The
Laplace sum-rules of pion currents is shown to violate this inequality unless
the and quark masses are sufficiently large, placing a lower bound on
, the SU(2)-invariant combination of the light-quark masses.Comment: 3 pages, latex, write-up of talk presented at DPF 200
The Role of the D13 (1520) Resonance in eta Electroproduction
We investigate the electroproduction of eta mesons below a center of momentum
energy of 1.6 GeV, with particular emphasis on the roles of the N*(1535) and
N*(1520) resonances. Using the effective Lagrangian approach, we show that the
transverse helicity amplitude of the N*(1535) can be extracted with good
accuracy from the new eta electroproduction data, under reasonable assumptions
for the strength of the longitudinal helicity amplitude. In addition, although
the differential cross section is found to to have a small sensitivity to the
N*(1520) resonance, it is shown that a recently completed double polarization
experiment is very sensitive to this resonance.Comment: 7 pages, Revtex, 3 figure
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