228 research outputs found
Wilhelminische Ostmarkenpolitik als infrastrukturelle Durchdringung? Masuren und der deutsch-polnische Antagonismus
Compton Scattering by the Nucleon
The status of Compton scattering by the nucleon at energies of the first and
second resonance is summarized. In addition to a general test of dispersion
theories and a precise determination of polarizabilities, the validities of
four fundamental sum rules are explored. {\it Recommended} averages of
experimental values for the electromagnetic polarizabilities and
spin-polarizabilities of the nucleon are determined: ,
, , (unit
fm), , (unit fm).Comment: version appearing in the conference proceeding
Magnetic polarizability of hadrons from lattice QCD
We extract the magnetic polarizability from the quadratic response of a
hadron's mass shift in progressively small static magnetic fields. The
calculation is done on a 24x12x12x24 lattice at a = 0.17 fm with an improved
gauge action and the clover quark action. The results are compared to those
from experiments and models where available.Comment: 3 pages, 3 figures, contribution to Lattice 2002 (spectrum
Electric Polarizability of Hadrons
The electric polarizability of a hadron allows an external electric field to
shift the hadron mass. We try to calculate the electric polarizability for
several hadrons from their quadratic response to the field at a=0.17fm using an
improved gauge field and the clover quark action. Results are compared to
experiment where available.Comment: 3 pgs, 5 figs, LATTICE2002(spectrum
Studies on the electromagnetic structure of the nucleon by free and quasi-free Compton scattering at MAMI (Mainz)
Using hydrogen and deuterium targets, Compton scattering by the proton and
neutron have been studied at the tagged photon beam of the MAMI (Mainz)
accelerator using different experimental setups. The theoretical tools for the
analysis of the experimental data have been investigated, as there are the
nonsubtracted dispersion theory and the theory of quasi-free reactions on the
proton and neutron bound in the deuteron. Experimental Compton scattering data
are understood in the first and second resonance region with good precision.
Precise electromagnetic polarizabilities and spin polarizabilities for the
proton and neutron have been determined
Quasi-free Photoproduction from the Bound Nucleon
Differential cross-sections for quasi-free photoproduction from the
proton and neutron bound in the deuteron have been measured for MeV at usind the Glasgow photon
tagger at MAMI, the Mainz 48 cm 64 cm NaI(Tl) photon
detector and the G\"ottingen SENECA recoil detector. For the proton
measurements made with both liquid deuterium and liquid hydrogen targets allow
direct comparison of "free" photoproduction cross-sections as extracted
from the bound proton data with experimental free cross sections which are
found to be in reasonable agreement below 320 MeV. At higher energies the
"free" cross sections extracted from quasifree data are significantly smaller
than the experimental free cross sections and theoretical predictions based on
multipole analysis. For the first time, "free" neutron cross sections have been
extracted in the -region. They are also in agreement with the
predictions from multipole analysis up to 320 MeV and significantly smaller at
higher photon energies
Electric polarizabilities of proton and neutron and the relativistic center-of-mass coordinate
We argue that the relativistic correction to the
center-of-mass vector can lead to the approximate equality of the proton and
neutron electric polarizabilities in the quark model. The explicit form of
depends only on the non-relativistic potential between
quarks. In particular, this correction is the same for the potential generated
by Lorentz-vector and -scalar interactions.Comment: 8 pages, LaTeX, conclusion extende
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