7,823 research outputs found
Comment on "A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy Ion Physics"
We critically discuss the recently developed quantum-mechanical equivalent
photon spectrum by Benesh et al. We point out that the key point, the strong
absorption in heavy ion collisions, is not treated adequately. Conclusions
drawn from such a spectrum are invalid. Equivalent photon spectra appropriate
for heavy ions, have been given before in quantal as well as semiclassical
versions and were found to be very satisfactory.Comment: 3 pages, LaTe
Production of QED pairs at small impact parameter in relativistic heavy ion collisions
The STAR collaboration at RHIC is measuring the production of
electron-positron pairs at small impact parameters, larger than but already
close to the range, where the ions interact strongly with each other. We
calculate the total cross section, as well as, differential distributions of
the pair production process with the electromagnetic excitation of both ions in
a semiclassical approach and within a lowest order QED calculation. We compare
the distribution of electron and positron with the one coming from the cross
section calculation without restriction on impact parameter. Finally we give an
outlook of possible results at the LHC.Comment: 15 pages, 8 figure
Stock return autocorrelations revisited: A quantile regression approach
The aim of this study is to provide a comprehensive description of the dependence pattern of stock returns by studying a range of quantiles of the conditional return distribution using quantile autoregression. This enables us in particular to study the behavior of extreme quantiles associated with large positive and negative returns in contrast to the central quantile which is closely related to the conditional mean in the least-squares regression framework. Our empirical results are based on 30 years of daily, weekly and monthly returns of the stocks comprised in the Dow Jones Stoxx 600 index. We find that lower quantiles exhibit positive dependence on past returns while upper quantiles are marked by negative dependence. This pattern holds when accounting for stock specific characteristics such as market capitalization, industry, or exposure to market risk. --stock return distribution,quantile autoregression,overreaction and underreaction
Electroweak corrections to production at hadron colliders
In this paper we present the results from a calculation of the full
electroweak one-loop corrections for vector-boson pair production at
hadron colliders. The cases of proton--antiproton as well as proton--proton
collisions, at the Tevatron and the LHC, respectively, are considered. Results
are presented for the distribution of the invariant mass and for the
transverse momentum of the final-state photon. The higher-order electroweak
effects are numerically significant, in particular for probing possible
anomalous gauge-boson couplings
Mixed top-bottom squark production at the LHC
We calculate cross sections for mixed stop-sbottom pair production at the
LHC, analogous to single-top production, a weak process involving the
W-t(i)-b(j) vertex. While coupling-suppressed relative to QCD same-flavor
squark pair production, the signal is distinctive due to heavy-flavor tagging
along with a possible same-sign lepton pair in the final state. SUSY
backgrounds can often be suppressed many orders of magnitude by taking
advantage of distinct kinematic differences from the signal. Measuring the rate
of this process would add significant additional information to that gathered
from other SUSY processes. If the stop and sbottom mixings can be determined
elsewhere, stop-sbottom production would provide for a measurement of the weak
squark gauge coupling and super-CKM vertex factor.Comment: typo corrected, comment on W-associated channel added, version to
appear in PR
Deep semi-supervised segmentation with weight-averaged consistency targets
Recently proposed techniques for semi-supervised learning such as Temporal
Ensembling and Mean Teacher have achieved state-of-the-art results in many
important classification benchmarks. In this work, we expand the Mean Teacher
approach to segmentation tasks and show that it can bring important
improvements in a realistic small data regime using a publicly available
multi-center dataset from the Magnetic Resonance Imaging (MRI) domain. We also
devise a method to solve the problems that arise when using traditional data
augmentation strategies for segmentation tasks on our new training scheme.Comment: 8 pages, 1 figure, accepted for DLMIA/MICCA
NIEL Dose Dependence for Solar Cells Irradiated with Electrons and Protons
The investigation of solar cells degradation and the prediction of its
end-of-life performance is of primary importance in the preparation of a space
mission. In the present work, we investigate the reduction of solar-cells'
maximum power resulting from irradiations with electrons and protons. Both GaAs
single junction and GaInP/GaAs/Ge triple junction solar cells were studied. The
results obtained indicate how i) the dominant radiation damaging mechanism is
due to atomic displacements, ii) the relative maximum power degradation is
almost independent of the type of incoming particle, i.e., iii) to a first
approximation, the fitted semi-empirical function expressing the decrease of
maximum power depends only on the absorbed NIEL dose, and iv) the actual
displacement threshold energy value (Ed=21 eV) accounts for annealing
treatments, mostly due to self-annealing induced effects. Thus, for a given
type of solar cell, a unique maximum power degradation curve can be determined
as a function of the absorbed NIEL dose. The latter expression allows one to
predict the performance of those solar cells in space radiation environment.Comment: To appear on the Proceedings of the 13th ICATPP Conference on
Astroparticle, Particle, Space Physics and Detectors for Physics
Applications, Villa Olmo (Como, Italy), 23--27 October, 2013, to be published
by World Scientific (Singapore
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