249 research outputs found
Simulation study of electron drift and gas multiplication in Micro Pixel Chamber
The physical processes of charge collection and gas multiplication of a Micro
Pixel Chamber (mu-PIC) were studied in detail using a three-dimensional
simulation. The collection efficiencies of primary electrons and gas
multiplication factors were calculated for several electrode structures. Based
on those studies, we analyzed the optimization of the electrode structure of
the mu-PIC, in order to obtain a high gas gain of more than 10^4 and a
simultaneous suppression of discharges. Consequently, we found that these
characteristics strongly depend on the substrate thickness and the anode
diameter of the mu-PIC. In addition, a gas gain of 10^5 would be expected for a
mu-PIC having a thick substrate of > 150um.Comment: 16 pages, 14 figures, Submitted to Nucl. Instr. Methods
Challenges in Hyperon Decays
We give an personal overview of some of the unsolved problems related to
hyperon decays. We cover nonleptonic decays, radiative decays and magnetic
moments. Some of the theoretical issues are also touched upon.Comment: Contribution to Workshop On Low-Energy Pbar Storage Ring (Pbar2000
Hyperon weak radiative decays in chiral perturbation theory
We investigate the leading-order amplitudes for weak radiative decays of
hyperons in chiral perturbation theory. We consistently include contributions
from the next-to-leading order weak-interaction Lagrangian. It is shown that
due to these terms Hara's theorem is violated. The data for the decays of
charged hyperons can be easily accounted for. However, at this order in the
chiral expansion, the four amplitudes for the decays of neutral hyperons
satisfy relations which are in disagreement with the data. The asymmetry
parameters for all the decays can not be accounted for without higher-order
terms. We shortly comment on the effect of the 27-plet part of the weak
interaction.Comment: 8 pages of REVTeX and using macro-package "feynman.tex" (available at
http://xxx.lanl.gov/ftp/hep-ph/papers/macros) for the 2 figure
Ab-initio electron scattering cross-sections and transport in liquid xenon
Ab-initio electron - liquid phase xenon fully differential cross-sections for
electrons scattering in liquid xenon are developed from a solution of the
Dirac-Fock scattering equations, using a recently developed framework [1] which
considers multipole polarizabilities, a non-local treatment of exchange, and
screening and coherent scattering effects. A multi-term solution of Boltzmann's
equation accounting for the full anisotropic nature of the differential
cross-section is used to calculate transport properties of excess electrons in
liquid xenon. The results were found to agree to within 25% of the measured
mobilities and characteristic energies over the reduced field range of 10^{-4}
to 1 Td. The accuracies are comparable to those achieved in the gas phase. A
simple model, informed by highly accurate gas-phase cross-sections, is
presented to transform highly accurate gas-phase cross-sections to improve the
liquid cross-sections, which was found to enhance the accuracy of the transport
coefficient calculations.Comment: 26 pages, 9 figures. arXiv admin note: text overlap with
arXiv:1503.0037
Modelling the behaviour of microbulk Micromegas in Xenon/trimethylamine gas
We model the response of a state of the art micro-hole single-stage charge
amplication device (`microbulk' Micromegas) in a gaseous atmosphere consisting
of Xenon/trimethylamine at various concentrations and pressures. The amplifying
structure, made with photo-lithographic techniques similar to those followed in
the fabrication of gas electron multipliers (GEMs), consisted of a 100 um-side
equilateral-triangle pattern with 50 um-diameter holes placed at its vertexes.
Once the primary electrons are guided into the holes by virtue of an optimized
field configuration, avalanches develop along the 50 um-height channels etched
out of the original doubly copper-clad polyimide foil. In order to properly
account for the strong field gradients at the holes' entrance as well as for
the fluctuations of the avalanche process (that ultimately determine the
achievable energy resolution), we abandoned the hydrodynamic framework,
resorting to a purely microscopic description of the electron trajectories as
obtained from elementary cross-sections. We show that achieving a satisfactory
description needs additional assumptions about atom-molecule (Penning) transfer
reactions and charge recombination to be made
- …