4,005 research outputs found
Hard breakup of the deuteron into two Delta-isobars
We study high energy photodisintegration of the deuteron into two
-isobars at large center of mass angles within the QCD hard
rescattering model (HRM). According to the HRM, the process develops in three
main steps: the photon knocks the quark from one of the nucleons in the
deuteron; the struck quark rescatters off a quark from the other nucleon
sharing the high energy of the photon; then the energetic quarks recombine into
two outgoing baryons which have large transverse momenta. Within the HRM, the
cross section is expressed through the amplitude of scattering which we evaluated based on the quark-interchange
model of hard hadronic scattering. Calculations show that the angular
distribution and the strength of the photodisintegration is mainly determined
by the properties of the
scattering. We predict that the cross section of
the deuteron breakup to is 4-5 times larger than that
of the breakup to the channel. Also, the angular
distributions for these two channels are markedly different. These can be
compared with the predictions based on the assumption that two hard
-isobars are the result of the disintegration of the preexisting
components of the deuteron wave function. In this case, one
expects the angular distributions and cross sections of the breakup in both and channels to be similar.Comment: 17 pages, 3 figure
A New Method for Searching for Free Fractional Charge Particles in Bulk Matter
We present a new experimental method for searching for free fractional charge
in bulk matter; this new method derives from the traditional Millikan liquid
drop method, but allows the use of much larger drops, 20 to 100 mm in diameter,
compared to the traditional method that uses drops less than 15 mm in diameter.
These larger drops provide the substantial advantage that it is then much
easier to consistently generate drops containing liquid suspensions of powdered
meteorites and other special minerals. These materials are of great importance
in bulk searches for fractional charge particles that may have been produced in
the early universe.Comment: 17 pages, 5 figures in a singl PDF file (created from WORD Doc.).
Submitted to Review of Scientific Instrument
Search for Free Fractional Electric Charge Elementary Particles
We have carried out a direct search in bulk matter for free fractional
electric charge elementary particles using the largest mass single sample ever
studied - about 17.4 mg of silicone oil. The search used an improved and highly
automated Millikan oil drop technique. No evidence for fractional charge
particles was found. The concentration of particles with fractional charge more
than 0.16e (e being the magnitude of the electron charge) from the nearest
integer charge is less than particles per nucleon with 95%
confidence.Comment: 10 pages,LaTeX, 4 PS figures, submitted to PR
Measurement of Dielectric Suppression of Bremsstrahlung
In 1953, Ter-Mikaelian predicted that the bremsstrahlung of low energy
photons in a medium is suppressed because of interactions between the produced
photon and the electrons in the medium. This suppression occurs because the
emission takes place over on a long distance scale, allowing for destructive
interference between different instantaneous photon emission amplitudes. We
present here measurements of bremsstrahlung cross sections of 200 keV to 20 MeV
photons produced by 8 and 25 GeV electrons in carbon and gold targets. Our data
shows that dielectric suppression occurs at the predicted level, reducing the
cross section up to 75 percent in our data.Comment: 11 pages, format is postscript file, gzip-ed, uuencode-e
Dilepton Production in Nucleon-Nucleon Reactions With and Without Hadronic Inelasticities
We calculate elementary proton-proton and neutron-proton bremsstrahlung and
their contribution to the invariant mass distribution. At 4.9 GeV, the
proton-proton contribution is larger than neutron-proton, but it is small
compared to recent data. We then make a first calculation of bremsstrahlung in
nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the
many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung
by more than an order of magnitude in the low-mass region. When the
bremsstrahlung contributions are summed with Dalitz decay of the ,
radiative decay of the and from two-pion annihilation, the result
matches recent high statistics proton-proton data from the Dilepton
Spectrometer collaboration.Comment: 1+17 pages plus 11 PostScript figures uuencoded and appended,
McGill/93-9, TPI-MINN-93/18-
Bremsstrahlung Suppression due to the LPM and Dielectric Effects in a Variety of Materials
The cross section for bremsstrahlung from highly relativistic particles is
suppressed due to interference caused by multiple scattering in dense media,
and due to photon interactions with the electrons in all materials. We present
here a detailed study of bremsstrahlung production of 200 keV to 500 MeV
photons from 8 and 25 GeV electrons traversing a variety of target materials.
For most targets, we observe the expected suppressions to a good accuracy. We
observe that finite thickness effects are important for thin targets.Comment: 52 pages, 13 figures (incorporated in the revtex LaTeX file
Distinct subsets of unmyelinated primary sensory fibers mediate behavioral responses to noxious thermal and mechanical stimuli
Behavioral responses to painful stimuli require peripheral sensory neurons called nociceptors. Electrophysiological studies show that most C-fiber nociceptors are polymodal (i.e., respond to multiple noxious stimulus modalities, such as mechanical and thermal); nevertheless, these stimuli are perceived as distinct. Therefore, it is believed that discrimination among these modalities only occurs at spinal or supraspinal levels of processing. Here, we provide evidence to the contrary. Genetic ablation in adulthood of unmyelinated sensory neurons expressing the G protein-coupled receptor Mrgprd reduces behavioral sensitivity to noxious mechanical stimuli but not to heat or cold stimuli. Conversely, pharmacological ablation of the central branches of TRPV1+ nociceptors, which constitute a nonoverlapping population, selectively abolishes noxious heat pain sensitivity. Combined elimination of both populations yielded an additive phenotype with no additional behavioral deficits, ruling out a redundant contribution of these populations to heat and mechanical pain sensitivity. This double-dissociation suggests that the brain can distinguish different noxious stimulus modalities from the earliest stages of sensory processing
QCD Rescattering and High Energy Two-Body Photodisintegration of the Deuteron
Photon absorption by a quark in one nucleon followed by its high momentum
transfer interaction with a quark in the other may produce two final-state
nucleons with high relative momentum. We sum the relevant quark rescattering
diagrams, to show that the scattering amplitude depends on a convolution
between the large angle scattering amplitude, the hard photon-quark
interaction vertex and the low-momentum deuteron wave function. The computed
absolute values of the cross section are in reasonable agreement with the data.Comment: 4 pages, revised version to be published in Phys. Rev. Let
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