9,440 research outputs found
Finite Width Effects and Gauge Invariance in Radiative Production and Decay
The naive implementation of finite width effects in processes involving
unstable particles can violate gauge invariance. For the example of radiative
production and decay, , at tree level, it is
demonstrated how gauge invariance is restored by including the imaginary part
of triangle graphs in addition to resumming the imaginary contributions to the
vacuum polarization. Monte Carlo results are presented for the Fermilab
Tevatron.Comment: 10 pages, Revtex, 3 figures submitted separately as uuencoded tarred
postscript files, the complete paper is available at
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-878.ps.Z or
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-878.ps.
Comment on "A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy Ion Physics"
We critically discuss the recently developed quantum-mechanical equivalent
photon spectrum by Benesh et al. We point out that the key point, the strong
absorption in heavy ion collisions, is not treated adequately. Conclusions
drawn from such a spectrum are invalid. Equivalent photon spectra appropriate
for heavy ions, have been given before in quantal as well as semiclassical
versions and were found to be very satisfactory.Comment: 3 pages, LaTe
Quark resonances and high E_t jets
Possible spin-3/2 quark resonances would have a significant effect on high
E_{\mbox{\rm t}} jet production through their contribution to the subprocess
. Such enhancements are compared to a, recently
reported, anomaly in inclusive jet production at the CDF detector.Comment: 7 pages set in RevTex with four postscript figures appended- all
uuencode
Hadron collider limits on anomalous couplings
A next-to-leading log calculation of the reactions and
is presented including a tri-boson
gauge coupling from non-Standard Model contributions. Two approaches are made
for comparison. The first approach considers the tri-boson coupling
as being uniquely fixed by tree level unitarity at high energies to its
Standard Model form and, consequently, suppresses the non-Standard Model
contributions with form factors. The second approach is to ignore such
considerations and calculate the contributions to non-Standard Model tri-boson
gauge couplings without such suppressions. It is found that at Tevatron
energies, the two approaches do not differ much in quantitative results, while
at Large Hadron Collider (LHC) energies the two approaches give significantly
different predictions for production rates. At the Tevatron and LHC, however,
the sensitivity limits on the anomalous coupling of are too weak to
usefully constrain parameters in effective Lagrangian models.Comment: Revtex 23 pages + 8 figures, UIOWA-94-1
E0 emission in alpha + ^12C fusion at astrophysical energies
We show that E0 emission in alpha + ^12C fusion at astrophysically
interesting energies is negligible compared to E1 and E2 emission.Comment: submitted to Phys. Rev. C, Brief Report
Exclusive meson pair production in peripheral ultrarelativistic heavy ion collisions
The cross sections for exclusive and meson pair
production in peripheral nucleus - nucleus collisions are calculated and
several differential distributions are presented. The calculation of the
elementary cross section is done within the
heavy-quark approximation and in the Brodsky- Lapage formalism with
distribution amplitudes describing recent CLEO data on leptonic decay.
Realistic (Fourier transform of charge density) charge form factors of nuclei
are used to generate photon flux factors. Absorption effects are discussed and
quantified. The cross sections of a few nb are predicted for RHIC and of a few
hundreds of nb for LHC with details depending on the approximation made in
calculating elementary cross sections.Comment: 11 pages, 8 figure
Logarithmic electroweak corrections to gauge-boson pair production at the LHC
We have studied the effects of the complete logarithmic electroweak O(alpha)
corrections on the production of vector-boson pairs WZ, ZZ, and WW at the LHC.
These corrections are implemented into a Monte Carlo program for pp -> 4f
(+\gamma) with final states involving four or two leptons using the double-pole
approximation. We numerically investigate purely leptonic final states and find
that electroweak corrections lower the predictions by 5-30% in the physically
interesting region of large di-boson invariant mass and large angle of the
produced vector bosons.Comment: 47 pages, LaTeX, 18 eps figure
Periodicity and Growth in a Lattice Gas with Dynamical Geometry
We study a one-dimensional lattice gas "dynamical geometry model" in which
local reversible interactions of counter-rotating groups of particles on a ring
can create or destroy lattice sites. We exhibit many periodic orbits and and
show that all other solutions have asymptotically growing lattice length in
both directions of time. We explain why the length grows as in all
cases examined. We completely solve the dynamics for small numbers of particles
with arbitrary initial conditions.Comment: 18 pages, LaTe
Synthesis of extracellular matrix components by human ciliary muscle cells in culture
The production and spatial organization of connective tissue components in ciliary muscle cell cultures was studied with immunohistochemical and ultrastructural methods. Antibodies against collagen types IV and VI, fibronectin and laminin were used. Laminin stains as pericellular network surrounding individual muscle cells. Type IV collagen shows positive cytoplasmic staining and only small foci of extracellular immunofluorescence. Staining for type VI collagen and fibronectin is seen near the ends of the bipolar cells, while the lateral sides of the cells remain unstained. Electronmicroscopy shows that cultured ciliary muscle cells are surrounded by an incomplete basal lamina. In addition, bundles of 5-20 nm thick extracellular microfibrils are seen. The bundles are oriented parallel to the axis of the cells and are in close contact with the cell membrane in areas where membrane-bound dense bands are formed. Immunoelectronmicroscopy indicates that the bundles contain fibronectin and type VI collagen fibrils. While the fibronectin fibrils approach the cell membrane directly, type VI collagen fibrils are usually separated from the cell membrane by fine fibrillous material of different nature. Quality and spatial organization of the extracellular material in ciliary muscle cell cultures shows marked similarities with the extracellular matrix of ciliary muscle in situ
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