1,320 research outputs found
A Comparative Numerical Study on GEM, MHSP and MSGC
In this work, we have tried to develop a detailed understanding of the
physical processes occurring in those variants of Micro Pattern Gas Detectors
(MPGDs) that share micro hole and micro strip geometry, like GEM, MHSP and MSGC
etc. Some of the important and fundamental characteristics of these detectors
such as gain, transparency, efficiency and their operational dependence on
different device parameters have been estimated following detailed numerical
simulation of the detector dynamics. We have used a relatively new simulation
framework developed especially for the MPGDs that combines packages such as
GARFIELD, neBEM, MAGBOLTZ and HEED. The results compare closely with the
available experimental data. This suggests the efficacy of the framework to
model the intricacies of these micro-structured detectors in addition to
providing insight into their inherent complex dynamical processes
Cosmic ray tests of a GEM-based TPC prototype operated in Ar-CF4-isobutane gas mixtures
Argon with an admixture of CF4 is expected to be a good candidate for the gas
mixture to be used for a time projection chamber (TPC) in the future linear
collider experiment because of its small transverse diffusion of drift
electrons especially under a strong magnetic field. In order to confirm the
superiority of this gas mixture over conventional TPC gases we carried out
cosmic ray tests using a GEM-based TPC operated mostly in Ar-CF4-isobutane
mixtures under 0 - 1 T axial magnetic fields. The measured gas properties such
as gas gain and transverse diffusion constant as well as the observed spatial
resolution are presented.Comment: 22 pages, 18 figures. Published in Nuclear Instruments and Methods in
Physics Research A. Fig. 3 in the introduction was corrected since it had not
been properly normalized. Minor corrections and no changes in the conclusio
Charmed Baryons with
The width of a recently discovered excited charmed-strange baryon, a
candidate for a state with spin 3/2, is calculated. In the absence of
configuration mixing between the ground-state (spin-1/2) charmed-strange baryon
and the spin-1/2 state lying about 95 MeV above it,
one finds and , where the tilde denotes the partial
width with kinematic factors removed. Assuming a kinematic factor for P-wave
decay of , one predicts MeV, while the channel is closed. Some
suggestions are given for detecting the , the spin-3/2 charmed
nonstrange baryon, and the , the spin-3/2 charmed doubly-strange
baryon.Comment: 11 pages, latex, 2 uuencoded figures sent separatel
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
Measurement of the Omega_c Lifetime
We present the measurement of the lifetime of the Omega_c we have performed
using three independent data samples from two different decay modes. Using a
Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c
decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts
normally used in charm analysis. The short but measurable lifetime of the
Omega_c is demonstrated by a clear enhancement of the signals at short but
finite decay lengths. Using a continuous maximum likelihood method we
determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs.
This makes the Omega_c the shortest living weakly decaying particle observed so
far. The short value of the lifetime confirms the predicted pattern of the
charmed baryon lifetimes and demonstrates that the strong interaction plays a
vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip
Changing the prehistory of Sindh and Las Bela coast: twenty-five years of Italian contribution
The paper discusses the prehistory of Lowr Sindh and Las Bela Coast, and the role played by the Italian archaeologists since the 1980's. New date are presented regarding mainly the radiocarbon chronology the Indus Delta settlement on rocky outcrops and the shell middens of Las Bela
Heavy Baryon Specroscopy from the Lattice
The results of an exploratory lattice study of heavy baryon spectroscopy are
presented. We have computed the full spectrum of the eight baryons containing a
single heavy quark, on a lattice at , using an
-improved fermion action. We discuss the lattice baryon operators and
give a method for isolating the contributions of the spin doublets
, and to the correlation
function of the relevant operator. We compare our results with the available
experimental data and find good agreement in both the charm and the beauty
sectors, despite the long extrapolation in the heavy quark mass needed in the
latter case. We also predict the masses of several undiscovered baryons. We
compute the \Lambda-\mbox{pseudoscalar meson} and mass
splittings. Our results, which have errors in the range , are in good
agreement with the experimental numbers. For the mass
splitting, we find results considerably smaller than the experimental values
for both the charm and the beauty baryons, although in the latter case the
experimental results are still preliminary. This is also the case for the
lattice results for the hyperfine splitting for the heavy mesons.Comment: 31 pages LaTex, with postscript figures include
Growth factor restriction impedes progression of wound healing following cataract surgery: identification of VEGF as a putative therapeutic target
Secondary visual loss occurs in millions of patients due to a wound-healing response, known as posterior capsule opacification (PCO), following cataract surgery. An intraocular lens (IOL) is implanted into residual lens tissue, known as the capsular bag, following cataract removal. Standard IOLs allow the anterior and posterior capsules to become physically connected. This places pressure on the IOL and improves contact with the underlying posterior capsule. New open bag IOL designs separate the anterior capsule and posterior capsules and further reduce PCO incidence. It is hypothesised that this results from reduced cytokine availability due to greater irrigation of the bag. We therefore explored the role of growth factor restriction on PCO using human lens cell and tissue culture models. We demonstrate that cytokine dilution, by increasing medium volume, significantly reduced cell coverage in both closed and open capsular bag models. This coincided with reduced cell density and myofibroblast formation. A screen of 27 cytokines identified nine candidates whose expression profile correlated with growth. In particular, VEGF was found to regulate cell survival, growth and myofibroblast formation. VEGF provides a therapeutic target to further manage PCO development and will yield best results when used in conjunction with open bag IOL designs
Characterisation of large area THGEMs and experimental measurement of the Townsend coefficients for CF4
Whilst the performance of small THGEMs is well known, here we consider the challenges in scaling these up to large area charge readouts. We first verify the expected gain of larger THGEMs by reporting experimental Townsend coefficients for a 10 cm diameter THGEM in low-pressure CF. Large area 50 cm by 50 cm THGEMs were sourced from a commercial PCB supplier and geometrical imperfections were observed which we quantified using an optical camera setup. The large area THGEMs were experimentally characterised at Boulby Underground Laboratory through a series of gain calibrations and alpha spectrum measurements. ANSYS, Magboltz and Garfield++ simulations of the design of a TPC based on the large area THGEMs are presented. We also consider their implications for directional dark matter research and potential applications within nuclear security
Search for the exotic Resonance in 340GeV/c -Nucleus Interactions
We report on a high statistics search for the resonance in
-nucleus collisions at 340GeV/c. No evidence for this resonance is
found in our data sample which contains 676000 candidates above
background. For the decay channel and the
kinematic range 0.150.9 we find a 3 upper limit for the
production cross section of 3.1 and 3.5 b per nucleon for reactions with
carbon and copper, respectively.Comment: 5 pages, 4 figures, modification of ref. 43 and 4
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