342 research outputs found
Dirac sea effects in scattering from nuclei
The ratio of to cross sections has been calculated
microscopically using a boson-exchange amplitude in which the and
mesons are dressed by the modifications of the Dirac sea in nuclear
matter. In spite of the fact that this dressing leads to a scaling of the
mesons effective mass in nuclear matter, the effect on the ratio is found
to be weak.Comment: 8 pages, LaTeX, 2 figures available upon request, LPTB-93-
Bubble Free Energy in Cosmological Phase Transitions
Free energy as a function of temperature and the bubble radius is determined
for spherical bubbles created in cosmological first order phase transitions.
The phase transition is assumed to be driven by an order parameter (e.g. a
Higgs field) with quartic potential. The definition of the bubble radius and
the corresponding generalized, curvature-dependent surface tensions are
discussed. In the free energy expansion in powers of the inverse radius, the
coefficients of the curvature term and the constant term are also calculated.Comment: 9 pages ( + 7 figures, available on request as a 130 kB Postscript
file or by fax or mail), plain Latex, HU-TFT-92-5
Measurement of quasi-elastic 12C(p,2p) scattering at high momentum transfer
We measured the high-momentum quasi-elastic 12C(p,2p) reaction (at center of
mass angle near 90 degrees) for 6 and 7.5 GeV/c incident protons. The
three-momentum components of both final state protons were measured and the
missing energy and momentum of the target proton in the nucleus were
determined.
The validity of the quasi-elastic picture was verified up to Fermi momenta of
about 450 MeV/c, where it might be questionable. Transverse and longitudinal
Fermi momentum distributions of the target proton were measured and compared to
independent particle models which do not reproduce the large momentum tails. We
also observed that the transverse Fermi distribution gets wider as the
longitudinal component increases in the beam direction, in contrast to a simple
Fermi gas model.Comment: 4 pages including 3 figure
Medium effects in K^+ nucleus interaction from consistent analysis of integral and differential cross sections
Self consistency in the analysis of transmission measurements for K^+ on
several nuclei in the momentum range of 500-700 MeV/c is achieved with a
"t_{eff}(rho)rho" potential and new results are derived for total cross
sections. The imaginary part of the t_{eff} amplitude is found to increase
linearly with the average nuclear density in excess of a threshold value. This
phenomenological density dependence of the K^+ nucleus optical potential also
gives rise to good agreement with recent measurements of differential cross
sections for elastic scattering of 715 MeV/c K^+ by Li^6 and C.Comment: 11 pages, RevTeX, 2 Postscript figures, submitted Phys. Lett.
CHIRAL SYMMETRY CONSTRAINTS ON THE INTERACTION WITH THE NUCLEAR PION CLOUD
The real part of the selfenergy for the interaction of the
with the pion nuclear cloud is evaluated in lowest order of chiral perturbation
theory and is found to be exactly zero in symmetric nuclear matter. This
removes uncertainties in that quantity found in former phenomenological
analyses and is supported by present experimental data on nucleus
scattering.Comment: 11 pp, LaTeX file, 4 figures (appended as compressed tar files, uses
epsf.sty
Surface Tension at Finite Tempearture in the MIT Bag Model
At the surface tension in the MIT bag model for a
single hadron is known to be negligible as compared to the bag pressure . We show that at finite temperature it has a substantial value of 50 -
70 MeV which also differ from hadron to hadron. We also find that the dynamics
of the Quark-Gluon Plasma is such that the creation of hybrids
with massive quarks will predominate over the creation of
mesons.Comment: Substantial changes in the revised version and a new author included,
13 pages in Latex and one figur
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