405 research outputs found
From Euclidean to Minkowski space with the Cauchy-Riemann equations
We present an elementary method to obtain Green's functions in
non-perturbative quantum field theory in Minkowski space from calculated
Green's functions in Euclidean space. Since in non-perturbative field theory
the analytical structure of amplitudes is many times unknown, especially in the
presence of confined fields, dispersive representations suffer from systematic
uncertainties. Therefore we suggest to use the Cauchy-Riemann equations, that
perform the analytical continuation without assuming global information on the
function in the entire complex plane, only in the region through which the
equations are solved. We use as example the quark propagator in Landau gauge
Quantum Chromodynamics, that is known from lattice and Dyson-Schwinger studies
in Euclidean space. The drawback of the method is the instability of the
Cauchy-Riemann equations to high-frequency noise, that makes difficult to
achieve good accuracy. We also point out a few curiosities related to the Wick
rotation.Comment: 12 pages in EPJ double-column format, 16 figures. This version: added
paragraph, two reference
A comprehensive study of rate capability in Multi-Wire Proportional Chambers
Systematic measurements on the rate capability of thin MWPCs operated in
Xenon, Argon and Neon mixtures using CO2 as UV-quencher are presented. A good
agreement between data and existing models has been found, allowing us to
present the rate capability of MWPCs in a comprehensive way and ultimately
connect it with the mobilities of the drifting ions.Comment: 29 pages, 18 figure
Solving the Bethe-Salpeter equation for a pseudoscalar meson in Minkowski space
A new method of solution of the Bethe-Salpeter equation for a pseudoscalar
quark-antiquark bound state is proposed. With the help of an integral
representation, the results are directly obtained in Minkowski space. Dressing
of Green's functions is naturally taken into account, thus providing the
possible inclusion of a running coupling constant as well as quark propagators.
First numerical results are presented for a simplified ladder approximation
Thick GEM-like multipliers - a simple solution for large area UV-RICH detectors
We report on the properties of thick GEM-like (THGEM) electron multipliers
made of 0.4 mm thick double-sided Cu-clad G-10 plates, perforated with a dense
hexagonal array of 0.3 mm diameter drilled holes. Photon detectors comprising
THGEMs coupled to semi-transparent CsI photocathodes or reflective ones
deposited on the THGEM surface were studied with Ar/CO2 (70:30), Ar/CH4 (95:5),
CH4 and CF4. Gains of ~100000 or exceeding 1000000 were reached with single- or
double-THGEM, respectively; the signals have 5-10 ns rise times. The electric
field configurations at the THGEM electrodes result in an efficient extraction
of photoelectrons and their focusing into the holes; this occurs already at
rather low gains, below 100. These detectors, with single-photon sensitivity
and with expected sub-millimeter localization, can operate at MHz/mm2 rates. We
discuss their prospects for large-area UV-photon imaging for RICH.Comment: 5 pages, 6 figure
Beam tests of the gas electron multiplier
We describe the results of systematic measurements, carried out with single and double GEM detectors with printed circuit read-out and having an active area 10x10 cm , both in the laboratory and in a high energy charged particles beam at CERN. Using fast analogue readout electronics, we demonstrate efficiencies for minimum ionizing particles close to 100%, with typical signal/noise ratios above 50 and up to 10 for the single and double GEM configuration, respectively, and a time resolution of 15 ns fwhm. Localization accuracies around 40 mm rms have been obtained for perpendicular tracks, degrading to 200 mm at 20° of incidence to the normal. Operated in a non-flammable gas mixture (argon-carbon dioxide), GEM detectors are robust, light and cheap to manufacture, and offer excellent performances and reliability suited for use in the harsh environments met at high luminosity colliders
Hybrid Textures of Neutrinos
We present numerical and comprehensive analyses of the sixty hybrid textures
of neutrinos, which have an equality of matrix elements and one zero. These
textures are possibly derived from the discrete symmetry. Only six textures
among sixty ones are excluded by the present experimental data. Since there are
many textures which give similar predictions, the textures are classified based
on the numerical results. The neutrinoless double beta decay is also examined
in these textures. Our results suggest that there remain still rich structures
of the neutrino mass matrix in the phenomenological point of view.Comment: 19 pages, 9 figures; analytical discussions added, table and
reference adde
Aging measurements with the gas electron multiplier (GEM)
Continuing previous aging measurements with detectors based on the Gas Electron Multiplier (GEM), a cm triple-GEM detector, as used in the small area tracking of the COMPASS experiment at CERN, was investigated. With a detector identical to those installed in the experiment, long-term, high-rate exposures to keV X-ray radiation were performed to study its aging properties. In standard operation conditions, with Ar:CO (70:30) filling and operated at an effective gain of , no change in gain and energy resolution is observed after collecting a total charge of 7mC/mm, corresponding to seven years of normal operation. This observation confirms previous results demonstrating the relative insensitivity of GEM detectors to aging, even when manufactured with common materials
MICROMEGAS chambers for hadronic calorimetry at a future linear collider
Prototypes of MICROMEGAS chambers, using bulk technology and analog readout,
with 1x1cm2 readout segmentation have been built and tested. Measurements in
Ar/iC4H10 (95/5) and Ar/CO2 (80/20) are reported. The dependency of the
prototypes gas gain versus pressure, gas temperature and amplification gap
thickness variations has been measured with an 55Fe source and a method for
temperature and pressure correction of data is presented. A stack of four
chambers has been tested in 200GeV/c and 7GeV/c muon and pion beams
respectively. Measurements of response uniformity, detection efficiency and hit
multiplicity are reported. A bulk MICROMEGAS prototype with embedded digital
readout electronics has been assembled and tested. The chamber layout and first
results are presented
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