794 research outputs found
Some exact analytical results and a semi-empirical formula for single electron ionization induced by ultrarelativistic heavy ions
The delta function gauge of the electromagnetic potential allows
semiclassical formulas to be obtained for the probability of exciting a single
electron out of the ground state in an ultrarelativistic heavy ion reaction.
Exact formulas have been obtained in the limits of zero impact parameter and
large, perturbative, impact parameter. The perturbative impact parameter result
can be exploited to obtain a semi-empirical cross section formula of the form,
sigma = A ln(gamma) + B, for single electron ionization. A and B can be
evaluated for any combination of target and projectile, and the resulting
simple formula is good at all ultrarelativistic energies. The analytical form
of A and B elucidates a result previously found in numerical calculations:
scaled ionization cross sections decrease with increasing charge of the nucleus
being ionized. The cross section values obtained from the present formula are
in good agreement with recent CERN SPS data from a Pb beam on various nuclear
targets.Comment: 14 pages, latex, revtex source, no figure
Seismic Evaluation and Remediation of Embankment Dam
The seismic stability of the Croton Dam left embankment, was evaluated for potential earthquake ground motions. Field and laboratory test results were used to characterize the static and dynamic properties of the embankment and foundation materials. Results showed liquefaction and strength loss in certain zones of the embankment resulting in large deformation of the slope. Remediation of these areas of the dam was necessary. Various techniques were evaluated including drainage, construction of a berm at toe, vibro-grouted stone columns and compaction grouting. Compaction grouting was selected
Suppression of Heavy Ion gamma gamma Production of the Higgs by Coulomb Dissociation
Predicted two-photon Higgs production with heavy ions at LHC is shown to be
reduced due to the large Coulomb dissociation cross section. Incorporating the
effect of dissociation reduces the production of a 100 GeV Higgs by about a
factor of three compared to rates in the literature calculated without this
effect.Comment: 5 pages, latex, revtex source, two postscript figure
Bound-free pair production in ultra-relativistic ion collisions at the LHC collider: Analytic approach to the total and differential cross sections
A theoretical investigation of the bound-free electron-positron pair
production in relativistic heavy ion collisions is presented. Special attention
is paid to the positrons emitted under large angles with respect to the beam
direction. The measurement of these positrons in coincidence with the
down--charged ions is in principle feasible by LHC experiments. In order to
provide reliable estimates for such measurements, we employ the equivalent
photon approximation together with the Sauter approach and derive simple
analytic expressions for the differential pair--production cross section, which
compare favorably to the results of available numerical calculations. Based on
the analytic expressions, detailed calculations are performed for collisions of
bare Pb ions, taking typical experimental conditions of the LHC
experiments into account. We find that the expected count rate strongly depends
on the experimental parameters and may be significantly enhanced by increasing
the positron-detector acceptance cone.Comment: 10 pages, 4 figure
The Solar Neutrino Puzzle: An Oscillation Solution with Maximal Neutrino Mixing
If, as suggested by the SuperKamiokande results, the mu neutrino and tau
neutrino are maximally and ``rapidly'' mixed, this alone determines the mapping
from current to mass eigenstates up to one rotation angle (theta) mixing the
electron neutrino ``more slowly'', with an equal combination of the mu neutrino
and tau neutrino. For sin 2 theta = 1, the resulting minimal number of free
parameters, yet maximal mixing, shows agreement between extant observations of
solar neutrinos and predictions by the standard solar model with minor
modifications.Comment: 10 pages, latex, revtex source, two postscript figure
Probing the structure of the cold dark matter halo with ancient mica
Mica can store (for >1 Gy) etchable tracks caused by atoms recoiling from
WIMPs. Ancient mica is a directional detector despite the complex motions it
makes with respect to the WIMP "wind". We can exploit the properties of
directionality and long integration time to probe for structure in the dark
matter halo of our galaxy. We compute a sample of possible signals in mica for
a plausible model of halo structure.Comment: 7 pages, 2 figure
Aging dynamics of non-linear elastic interfaces: the Kardar-Parisi-Zhang equation
In this work, the out-of-equilibrium dynamics of the Kardar-Parisi-Zhang
equation in (1+1) dimensions is studied by means of numerical simulations,
focussing on the two-times evolution of an interface in the absence of any
disordered environment. This work shows that even in this simple case, a rich
aging behavior develops. A multiplicative aging scenario for the two-times
roughness of the system is observed, characterized by the same growth exponent
as in the stationary regime. The analysis permits the identification of the
relevant growing correlation length, accounting for the important scaling
variables in the system. The distribution function of the two-times roughness
is also computed and described in terms of a generalized scaling relation.
These results give good insight into the glassy dynamics of the important case
of a non-linear elastic line in a disordered medium.Comment: 14 pages, 6 figure
The Role of Antimatter Searches in the Hunt for Supersymmetric Dark Matter
We analyze the antimatter yield of supersymmetric (SUSY) models with large
neutralino annihilation cross sections. We introduce three benchmark scenarios,
respectively featuring bino, wino and higgsino-like lightest neutralinos, and
we study in detail the resulting antimatter spectral features. We carry out a
systematic and transparent comparison between current and future prospects for
direct detection, neutrino telescopes and antimatter searches. We demonstrate
that often, in the models we consider, antimatter searches are the only
detection channel which already constrains the SUSY parameter space.
Particularly large antiprotons fluxes are expected for wino-like lightest
neutralinos, while significant antideuteron fluxes result from resonantly
annihilating binos. We introduce a simple and general recipe which allows to
assess the visibility of a given SUSY model at future antimatter search
facilities. We provide evidence that upcoming space-based experiments, like
PAMELA or AMS, are going to be, in many cases, the unique open road towards
dark matter discovery.Comment: 34 pages, 18 figures; V2: misprints in the labels of fig. 2,3 and 5
correcte
Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites
Annihilating dark matter particles produce roughly as much power in electrons
and positrons as in gamma ray photons. The charged particles lose essentially
all of their energy to inverse Compton and synchrotron processes in the
galactic environment. We discuss the diffuse signature of dark matter
annihilations in satellites of the Milky Way (which may be optically dark with
few or no stars), providing a tail of emission trailing the satellite in its
orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron
emission at radio wavelengths might be seen. We discuss the possibility of
detecting these signals with current and future observations, in particular
EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure
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