40,922 research outputs found
Prompt Photon plus Charm Production at Next-to-Leading Order in QCD
The two particle inclusive cross section for the reaction is studied in perturbative quantum
chromodynamics at order . Differential distributions are
provided for various observables, and a comparison is made with data from the
CDF collaboration.Comment: 4 pages, LaTeX, uses stwol.sty, 6 postscript figures. Invited paper
presented by E. L. Berger at the 28th International Conference on High Energy
Physics, Warsaw, Poland, July 25 - 31, 199
Associated Production of Charm and a Hard Photon
The two particle inclusive cross section for the reaction is studied in perturbative quantum
chromodynamics at order , for large values of the transverse
momentum of the prompt photon and charm quark. Two different techniques are
used in performing the phase-space integrals; the first is purely analytical,
and the second is a combination of analytic and Monte Carlo integration
methods. The second, more versatile technique facilitates imposition of photon
isolation restrictions and other selections of relevance in experiments.
Differential distributions are provided for various observables, and a
comparison is made with preliminary data from the CDF collaboration.Comment: 6 pages. Latex file plus 4 ps files of figures submitted togther in
uuencoded form; invited talk presented by L. E. Gordon at the XXXI Rencontres
de Moriond on QCD and High Energy Hadronic Interactions, Les Arcs, France,
March, 199
Polarized Double Photon Production in QCD to Order
We present a complete order analysis of the process with polarized initial states, previously studied by us with
leading order structure functions. We include in our calculation new sets of
parton densities evolved in NLO QCD, such as those of Gehrmann and Stirling and
of Gl\"{u}ck et al., which incorporate the new anomalous dimensions of Mertig
and Van Neerven in the evolution equation. A detailed phenomenological analysis
is also given which includes the photon isolation. Our results indicate that
the asymmetries, although not very large, should be substantial enough at RHIC
energies to be measurable in future planned experiments.Comment: 29 pages revtex, 13 psfig
Distribution and Status of Rare and Endangered Mussels (Mollusca: Margaritiferidae, Unionidae) in Arkansas
Knowledge of the distribution and population status of freshwater bivalves occurring in Arkansas has increased markedly during the past decade. Sufficient data has become available to delineate species which are rare and/or endangered within the state. Historical and recent records from Arkansas exist for four mussels currently listed as federally endangered species: the fat pocketbook (Potamilus capax), the pink mucket (Lampsilis orbiculata), Curtis\u27 pearly mussel (Epioblasma florentina curtisi), and the turgid-blossom pearly mussel (Epioblasma turgidula). Ten additional mussels which occur or were thought to occur in Arkansas are being considered for federal protection by the United States Fish and Wildlife Service. Several other taxa may warrant protective status
Ionosphere/microwave beam interaction study
A solar power satellite microwave power density of 20mw sq cm was confirmed as the level where nonlinear interactions may occur in the ionosphere, particularly at 100 km altitude. Radio wave heating at this altitude, produced at the Arecibo Observatory, yielded negative results for radio wave heating of an underdense ionosphere. Overdense heating produced striations in the ionosphere which may cause severe radio frequency interference problems under certain conditions. The effects of thermal self-focusing are shown to be limited severely geographically. The aspect sensitivity of field-aligned striations makes interference-free regions above magnetic latitude about 60 deg. A test program is proposed to simulate the interaction of the SPS beam with the ionosphere, to measure the effects of the interaction on the ionosphere and on communication and navigation systems, and to interpret the results
Production of a Prompt Photon in Association with Charm at Next-to-Leading Order in QCD
A second order, , calculation in perturbative quantum
chromodynamics of the two particle inclusive cross section is presented for the
reaction for large values of the
transverse momentum of the prompt photon and charm quark. The combination of
analytic and Monte Carlo integration methods used here to perform phase-space
integrations facilitates imposition of photon isolation restrictions and other
selections of relevance in experiments. Differential distributions are provided
for various observables. Positive correlations in rapidity are predicted.Comment: 27 pages in RevTex plus 14 figures in one compressed PS fil
Prompt Photon Plus Jet Photoproduction at HERA at Next-to-Leading Order in QCD
The cross section for photoproduction of an isolated prompt photon in
association with a jet is studied in Next-to-Leading Order. The kinematics are
those appropriate for the DESY collider HERA. The effects on the cross
section of various experimental cuts including isolation cuts on the photon is
examined. Comparisons with the ZEUS preliminary data using two parametrizations
of the photon structure function is made, and good agreement is found. The data
is not yet precise enough to make a distinction between various models for the
photon structure function.Comment: Uses eps
Shock effects in plagioclase feldspar from the Mistastin Lake impact structure, Canada
Shock metamorphism, caused by hypervelocity impact, is a poorly understood process in feldspar due to the complexity of the crystal structure, the relative ease of weathering, and chemical variations, making optical studies of shocked feldspars challenging. Understanding shock metamorphism in feldspars, and plagioclase in particular, is vital for understanding the history of Earth's moon, Mars, and many other planetary bodies. We present here a comprehensive study of shock effects in andesine and labradorite from the Mistastin Lake impact structure, Labrador, Canada. Samples from a range of different settings were studied, from in situ central uplift materials to clasts from various breccias and impact melt rocks. Evidence of shock metamorphism includes undulose extinction, offset twins, kinked twins, alternate twin deformation, and partial to complete transformation to diaplectic plagioclase glass. In some cases, isotropization of alternating twin lamellae was observed. Planar deformation features (PDFs) are notably absent in the plagioclase, even when present in neighboring quartz grains. It is notable that various microlites, twin planes, and compositionally different lamellae could easily be mistaken for PDFs and so care must be taken. A pseudomorphous zeolite phase (levyne-Ca) was identified as a replacement mineral of diaplectic feldspar glass in some samples, which could, in some instances, also be potentially mistaken for PDFs. We suggest that the lack of PDFs in plagioclase could be due to a combination of structural controls relating to the crystal structure of different feldspars and/or the presence of existing planes of weakness in the form of twin and cleavage planes
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