1,785 research outputs found
The Geant4 Hadronic Verification Suite for the Cascade Energy Range
A Geant4 hadronic process verification suite has been designed to test and
optimize Geant4 hadronic models in the cascade energy range. It focuses on
quantities relevant to the LHC radiation environment and spallation source
targets. The general structure of the suite is presented, including the user
interface, stages of verification, management of experimental data, event
generation, and comparison of results to data. Verification results for the
newly released Binary cascade and Bertini cascade models are presented.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 5 pages, LaTeX, 3 eps figures. PSN
MOMT00
Diffractive Interaction and Scaling Violation in pp->pi^0 Interaction and GeV Excess in Galactic Diffuse Gamma-Ray Spectrum of EGRET
We present here a new calculation of the gamma-ray spectrum from pp->pi^0 in
the Galactic ridge environment. The calculation includes the diffractive pp
interaction and incorporates the Feynman scaling violation for the first time.
Galactic diffuse gamma-rays come, predominantly, from pi^0->gamma gamma in the
sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV
range ("GeV Excess") in the EGRET Galactic diffuse spectrum above the
prediction based on experimental pp->pi^0 cross-sections and the Feynman
scaling hypothesis. We show, in this work, that the diffractive process makes
the gamma-ray spectrum harder than the incident proton spectrum by ~0.05 in
power-law index, and, that the scaling violation produces 30-80% more pi^0 than
the scaling model for incident proton energies above 100GeV. Combination of the
two can explain about a half of the "GeV Excess" with the local cosmic proton
(power-law index ~2.7). The excess can be fully explained if the proton
spectral index in the Galactic ridge is a little harder (~0.2 in power-law
index) than the local spectrum. Given also in the paper is that the diffractive
process enhances e^+ over e^- and the scaling violation gives 50-100% higher
p-bar yield than without the violation, both in the multi-GeV range.Comment: 35 pages, 11 figures, to appear in Astrophysical Journa
Monte Carlo calculations for the ATLAS cavern background
A new application for simulating the ATLAS cavern background was developed. This was done using FLUGG, software that allows Geant4 geometry to be used within the FLUKA simulation framework. A Geant4 description of the ATLAS detector including its cavern was built from scratch for this application. In order to gain computing performance, our geometry is less detailed than that of GeoModel which is used in the full detector simulation, but good enough for the investigation of cavern background. Our geometry can also be used in a standalone Geant4 simulation. Thus it is possible to perform unbiased comparisons between Geant4 and FLUKA using the same complex geometry. We compared neutron and photon fluxes using the FLUKA-FLUGG application with the result of Geant4 simulations based on the QGSP_BERT and QGSP_BERT_HP physics lists. In all cases the same set of initial collision 4-vectors produced by the PHOJET event generator was used. The result from the QGSP_BERT_HP physics list, which uses the High Precision (HP) neutron model, is similar to the result of FLUKA-FLUGG and the differences in the fluxes between them are within 40% in most regions of the ATLAS cavern. The result from the QGSP_BERT physics list, which does not include the HP model, does not agree with either of the previous two results
Comparison of measurement and simulation of ATLAS cavern radiation background
Sixteen Medipix2 pixel detector based (MPX) devices were operated at various positions within the ATLAS detector and cavern continuously from early 2008 up to 2013. In addition to photons, each MPX detector is capable to detect charged particles, and neutrons as it is covered with a mask of converter materials dividing its area into regions sensitive to thermal or fast neutrons. The MPX detector network was effectively used for real-time measurements of the spectral characteristics and composition of complex radiation fields in ATLAS. This article reports comparison of the results of measurements performed with MPX detectors during the LHC operation period in 2010 and 2011 with Monte Carlo simulations results from the FLUGG and GCALOR codes. For the purpose of this comparison, the MPX detectors were operated in tracking mode with low threshold (8-10 keV) allowing one to distinguish among particle categories based on the recognition of track patterns left by the particles in the MPX sensitive layer. The comparison of measurements with simulations shows that the agreement between measured and simulated data is satisfactory in most cases within a factor of two
Recent Developments And Validations in Geant4 Hadronic Physics
The Geant4 hadronic models cover the entire range of energies required by calorimeters in new and planned experiments. The extension and improvement of the elastic, cascade, parameterized and quark-gluon string models will be discussed. Such improvements include the extension to more particle types, a review and correction of cross sections, and a better treatment of energy and momentum conservation. Concurrent with this development has been a validation program which includes comparisons with double differential cross sections. An ongoing hadronic shower validation will also be discussed which includes the examination of longitudinal shower shapes and the performance of the above models as well as their interaction with electromagnetic processes such as multiple scattering
Parameterization of Gamma, e^+/- and Neutrino Spectra Produced by p-p Interaction in Astronomical Environment
We present the yield and spectra of stable secondary particles (gamma, e^+/-,
nu_e, nubar_e, nu_mu, and nubar_mu) of p-p interaction in parameterized
formulae to facilitate calculations involving them in astronomical
environments. The formulae are derived on the up-to-date p-p interaction model
by [Kamae05] which incorporates the logarithmically rising inelastic
cross-section, the diffraction dissociation process, and the Feynman scaling
violation. To improve fidelity to experimental data in lower energies, two
baryon resonance contributions have been added: one representing Delta(1232)
and the other multiple resonances around 1600MeV/c^2. The parametrized formulae
predict that all secondary particle spectra be harder by about 0.05 in
power-law indices than that of the incident proton and their inclusive
cross-sections be larger than those predicted by p-p interaction models based
on the Feynman scaling.Comment: Errors and typos in Eqns 1-4 and Table 1 corrected and editorial
changes incorporate
Adiabatic compression and indirect detection of supersymmetric dark matter
Recent developments in the modelling of the dark matter distribution in our
Galaxy point out the necessity to consider some physical processes to satisfy
observational data. In particular, models with adiabatic compression, which
include the effect of the baryonic gas in the halo, increase significantly the
dark matter density in the central region of the Milky Way. On the other hand,
the non-universality in scalar and gaugino sectors of supergravity models can
also increase significantly the neutralino annihilation cross section. We show
that the combination of both effects gives rise to a gamma-ray flux arising
from the Galactic Center largely reachable by future experiments like GLAST. We
also analyse in this framework the EGRET excess data above 1 GeV, as well as
the recent data from CANGAROO and HESS. The analysis has been carried out
imposing the most recent experimental constraints, such as the lower bound on
the Higgs mass, the \bsg branching ratio, and the muon . In addition, the
recently improved upper bound on has also been taken
into account. The astrophysical (WMAP) bounds on the dark matter density have
also been imposed on the theoretical computation of the relic neutralino
density through thermal production.Comment: 32 pages, 11 figures, final version to appear in JCA
Placental syncytiotrophoblast constitutes a major barrier to vertical transmission of Listeria monocytogenes.
Listeria monocytogenes is an important cause of maternal-fetal infections and serves as a model organism to study these important but poorly understood events. L. monocytogenes can infect non-phagocytic cells by two means: direct invasion and cell-to-cell spread. The relative contribution of each method to placental infection is controversial, as is the anatomical site of invasion. Here, we report for the first time the use of first trimester placental organ cultures to quantitatively analyze L. monocytogenes infection of the human placenta. Contrary to previous reports, we found that the syncytiotrophoblast, which constitutes most of the placental surface and is bathed in maternal blood, was highly resistant to L. monocytogenes infection by either internalin-mediated invasion or cell-to-cell spread. Instead, extravillous cytotrophoblasts-which anchor the placenta in the decidua (uterine lining) and abundantly express E-cadherin-served as the primary portal of entry for L. monocytogenes from both extracellular and intracellular compartments. Subsequent bacterial dissemination to the villous stroma, where fetal capillaries are found, was hampered by further cellular and histological barriers. Our study suggests the placenta has evolved multiple mechanisms to resist pathogen infection, especially from maternal blood. These findings provide a novel explanation why almost all placental pathogens have intracellular life cycles: they may need maternal cells to reach the decidua and infect the placenta
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