931 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
Implications of muon anomalous magnetic moment for supersymmetric dark matter
The anomalous magnetic moment of the muon has recently been measured to be in
conflict with the Standard Model prediction with an excess of 2.6 sigma. Taking
the excess at face value as a measurement of the supersymmetric contribution,
we find that at 95% confidence level it imposes an upper bound of 500 GeV on
the neutralino mass and forbids higgsinos as being the bulk of cold dark
matter. Other implications for the astrophysical detection of neutralinos
include: an accessible minimum direct detection rate, lower bounds on the
indirect detection rate of neutrinos from the Sun and the Earth, and a
suppression of the intensity of gamma-ray lines from neutralino annihilations
in the galactic halo.Comment: 4 pages, 2 figures, revised version accepted for publication in
Physical Review Letter
Directional detection of Dark Matter
Among the many experimental techniques available, those providing directional
information have the potential of yielding an unambiguous observation of WIMPs
even in the presence of insidious backgrounds. A measurement of the
distribution of arrival direction of WIMPs can also discriminate between
Galactic Dark Matter halo models. In this article, I will discuss the
motivation for directional detectors and review the experimental techniques
used by the various experiments. I will then describe one of them, the DMTPC
detector, in more detail.Comment: 17 pages, 11 postscript figures, mini-review submitted to Modern
Physics Letters A (MPLA). Submitted to Modern Physics Letters A (MPLA
Impact parameter dependence of heavy ion e+ e- pair production to all orders in Z alpha
The heavy ion probability for continuum e+ e- pair production has been
calculated to all orders in Z alpha as a function of impact parameter. The
formula resulting from an exact solution of the semiclassical Dirac equation in
the ultrarelativistic limit is evaluated numerically. In a calculation of gamma
= 100 colliding Au ions the probability of e+ e- pair production is reduced
from the perturbation theory result throughout the impact parameter range.Comment: 20 pages, latex, revtex, 6 eps figures. Revised Phys. Rev. C version
with minor additions, one figure added, and added reference
Process 3 -> 3 and crossing symmetry violation
Using the Sudakov technique we sum the perturbation series for the process
and obtain the compact analytical expression for the amplitude of this
process, which takes into account all possible Coulomb interactions between
colliding particles. Compare it with the amplitude of the lepton pair
production in heavy ion collision i.e. in the process , we show that
crossing symmetry between this processes holds only if one neglects the
interaction of produced pair with ions (i.e. in the approximation
).Comment: LaTeX2e, 10 pages, 5 eps figure
Determination of Dark Matter Properties at High-Energy Colliders
If the cosmic dark matter consists of weakly-interacting massive particles,
these particles should be produced in reactions at the next generation of
high-energy accelerators. Measurements at these accelerators can then be used
to determine the microscopic properties of the dark matter. From this, we can
predict the cosmic density, the annihilation cross sections, and the cross
sections relevant to direct detection. In this paper, we present studies in
supersymmetry models with neutralino dark matter that give quantitative
estimates of the accuracy that can be expected. We show that these are well
matched to the requirements of anticipated astrophysical observations of dark
matter. The capabilities of the proposed International Linear Collider (ILC)
are expected to play a particularly important role in this study.Comment: 124 pages, 62 figures; corrections and new material in Section 2.6
(direct detection); misc. additional correction
Implications of muon anomalous magnetic moment for supersymmetric dark matter
Journal ArticleThe anomalous magnetic moment of the muon has recently been measured to be in conflict with the standard model prediction with an excess of 2.6s. Taking the excess at face value as a measurement of the supersymmetric contribution, we find that at 95% confidence level it imposes an upper bound of 500 GeV on the neutralino mass and forbids Higgsinos as being the bulk of cold dark matter. Other implications for the astrophysical detection of neutralinos include an accessible minimum direct detection rate, lower bounds on the indirect detection rate of neutrinos from the Sun and the Earth, and a suppression of the intensity of gamma ray lines from neutralino annihilations in the galactic halo
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