827 research outputs found
Heavy ion beam lifetimes at relativistic and ultrarelativistic colliders
The effects of higher order corrections in ultra-relativistic nuclear
collisions are considered. It is found that higher order contributions are
small at low energy, large at intermediate energy and small again at very high
energy. An explanation for this effect is given. This means that the
Weizsacker-Williams formula is a good approximation to use in calculating cross
sections and beam lifetimes at energies relevant to RHIC and LHC.Comment: 10 pages, 2 tables, 4 figure
Graviton Production in Relativistic Heavy-Ion Collisions
We study the feasibility of producing the graviton of the novel Kaluza-Klein
theory in which there are d large compact dimensions in addition to the 4
dimensions of Minkowski spacetime. We calculate the cross section for producing
such a graviton in nucleus-nucleus collisions via t-channel photon-photon
fusion using the semiclassical Weizsacker-Williams method and show that it can
exceed the cross section for graviton production in electron-positron
scattering by several orders of magnitude.Comment: 10 pages, 3 figures, accepted for publication in Physical Review
Radiation Models for Exposure Analyses in Deep Space
No abstract availabl
Threshold meson production and cosmic ray transport
An interesting accident of nature is that the peak of the cosmic ray
spectrum, for both protons and heavier nuclei, occurs near the pion production
threshold. The Boltzmann transport equation contains a term which is the cosmic
ray flux multiplied by the cross section. Therefore when considering pion and
kaon production from proton-proton reactions, small cross sections at low
energy can be as important as larger cross sections at higher energy. This is
also true for subthreshold kaon production in nuclear collisions, but not for
subthreshold pion production.Comment: 9 pages, 1 figur
Exclusive Production of Higgs Bosons in Hadron Colliders
We study the exclusive, double--diffractive production of the Standard Model
Higgs particle in hadronic collisions at LHC and FNAL (upgraded) energies. Such
a mechanism would provide an exceptionally clean signal for experimental
detection in which the usual penalty for triggering on the rare decays of the
Higgs could be avoided. In addition, because of the color singlet nature of the
hard interaction, factorization is expected to be preserved, allowing the
cross--section to be related to similar hard--diffractive events at HERA.
Starting from a Fock state expansion in perturbative QCD, we obtain an estimate
for the cross section in terms of the gluon structure functions squared of the
colliding hadrons. Unfortunately, our estimates yield a production rate well
below what is likely to be experimentally feasible.Comment: 17 pages, RevTeX file, four uufiled PostScript figures. UMPP #94-177.
(Revised version. Some mistakenly missing Feynman diagrams are now added.
Results do not change qualitatively. Paper reorganized.
Another exact inflationary solution
A new closed-form inflationary solution is given for a hyperbolic interaction
potential. The method used to arrive at this solution is outlined as it appears
possible to generate additional sets of equations which satisfy the model. In
addition a new form of decaying cosmological constant is presented.Comment: 10 pages, 0 figure
Relativistic Multiple Scattering Theory and the Relativistic Impulse Approximation
It is shown that a relativistic multiple scattering theory for hadron-nucleus
scattering can be consistently formulated in four-dimensions in the context of
meson exchange. We give a multiple scattering series for the optical potential
and discuss the differences between the relativistic and non-relativistic
versions. We develop the relativistic multiple scattering series by separating
out the one boson exchange term from the rest of the Feynman series. However
this particular separation is not absolutely necessary and we discuss how to
include other terms. We then show how to make a three-dimensional reduction for
hadron-nucleus scattering calculations and we find that the relative energy
prescription used in the elastic scattering equation should be consistent with
the one used in the free two-body t-matrix involved in the optical potential.
We also discuss what assumptions are involved in making a Dirac Relativistic
Impulse Approximation (RIA).Comment: 20 pages, 9 figures, Accepted for publication in Journal of Physics
A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy-Ion Physics
In a previous paper, we calculated the fully quantum-mechanical cross section
for electromagnetic excitation during peripheral heavy-ion collisions. Here, we
examine the sensitivity of that cross section to the detailed structure of the
projectile and target nuclei. At the transition energies relevant to nuclear
physics, we find the cross section to be weakly dependent on the projectile
charge radius, and to be sensitive to only the leading momentum-transfer
dependence of the target transition form factors. We exploit these facts to
derive a quantum-mechanical ``equivalent-photon spectrum'' valid in the
long-wavelength limit. This improved spectrum includes the effects of
projectile size, the finite longitudinal momentum transfer required by
kinematics, and the response of the target nucleus to the off-shell photon.Comment: 19 pages, 5 figure
Working with simple machines
A set of examples is provided that illustrate the use of work as applied to
simple machines. The ramp, pulley, lever and hydraulic press are common
experiences in the life of a student and their theoretical analysis therefore
makes the abstract concept of work more real. The mechanical advantage of each
of these systems is also discussed so that students can evaluate their
usefulness as machines.Comment: 9 pages, 4 figure
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