3,944 research outputs found
A Remark on the Width
The width, , is analysed in conjunction with the
total and hadronic widths, and . Assuming,
tentatively, that the present 2 discrepancy in will
substantiate as time goes on, for large values of it will be sufficient
to modify the vertex only. In contrast, for small values of
, the theoretical predictions for both the width into light quarks
and leptons as well as the vertex will have to be modified.Comment: 8 pages uuencoded postscript including 2 figure
ATLAS Monitored Drift Tube Chambers in E = 11 MeV Neutron Background
The influence of fast neutrons on the occupancy and the single tube
resolution of ATLAS muon drift detectors was investigated by exposing a chamber
built out of 3 layers of 3 short standard drift tubes to neutron flux-densities
of up to 16 kHz/cm2 at a neutron energy of E=11 MeV. Pulse shape capable NE213
scintillaton detectors and a calibrated BF3 neutron detector provided
monitoring of the neutron flux-density and energy. The sensitivity of the drift
chamber to the neutrons was measured to be 4*10-4 by comparing data sets with
and without neutron background. For the investigation of tracks of cosmic muons
two silicon-strip detectors above and underneath the chamber allow to compare
measured drift-radii with reference tracks. Alternatively, the single tube
resolution was determined using the triple-sum method. The comparison between
data with and without neutron irradiation shows only a marginal effect on the
resolution and little influence on the muon track reconstruction.Comment: 4 pages, 11 figures, conferenc
A Search for Vector Diquarks at the CERN LHC
Resonant production of the first generation vector diquarks at the CERN Large
Hadron Collider (LHC) is investigated. It is shown that the LHC will be able to
discover vector diquarks with masses up to 9 TeV for quark-diquark-quark
coupling alpha_(D)=0.1 and 4 TeV for alpha_(D)=5x10^(-4).Comment: 9 pages, 4 tables, 4 figure
Z' Physics
The limits on extra neutral gauge bosons, which could be reached at LEP2, are
reviewed. Exclusion and discovery limits are discussed for f\bar f and WW
production.Comment: 20 pages Latex, 7 figures included by epsfig, Contribution to the
Proceedings the workshop "Physics at LEP2", Geneva, 199
Electron spin resonance and exchange paths in the orthorhombic dimer system Sr2VO4
We report on magnetization and electron spin resonance (ESR) measurements of
SrVO with orthorhombic symmetry. In this dimer system the
ions are in tetrahedral environment and are coupled by an antiferromagnetic
intra-dimer exchange constant 100 K to form a singlet ground
state without any phase transitions between room temperature and 2 K. Based on
an extended-H\"{u}ckel-Tight-Binding analysis we identify the strongest
exchange interaction to occur between two inequivalent vanadium sites via two
intermediate oxygen ions. The ESR absorption spectra can be well described by a
single Lorentzian line with an effective g-factor = 1.89. The temperature
dependence of the ESR intensity is well described by a dimer model in agreement
with the magnetization data. The temperature dependence of the ESR linewidth
can be modeled by a superposition of a linear increase with temperature with a
slope = 1.35 Oe/K and a thermally activated behavior with an
activation energy = 1418 K, both of which point to spin-phonon
coupling as the dominant relaxation mechanism in this compound.Comment: 5 pages, 4 figure
Temperature Studies for ATLAS MDT BOS Chambers
Data sets with high statistics taken at the cosmic ray facility, equipped
with 3 ATLAS BOS MDT chambers, in Garching (Munich) have been used to study
temperature and pressure effects on gas gain and drifttime. The deformation of
a thermally expanded chamber was reconstructed using the internal RasNik
alignment monitoring system and the tracks from cosmic data. For these studies
a heating system was designed to increase the temperature of the middle chamber
by up to 20 Kelvins over room temperature. For comparison the temperature
effects on gas properties have been simulated with Garfield. The maximum
drifttime decreased under temperature raise by -2.21 +- 0.08 ns/K, in agreement
with the results of pressure variations and the Garfield simulation. The
increased temperatures led to a linear increase of the gas gain of about 2.1%
1/K. The chamber deformation has been analyzed with the help of reconstructed
tracks. By the comparison of the tracks through the reference chambers with
these through the test chamber the thermal expansion has been reconstructed and
the result shows agreement with the theoretical expansion coefficient. As the
wires are fixed at the end of the chamber, the wire position calculation can
not provide a conclusion for the chamber middle. The complete deformation has
been identified with the analysis of the monitoring system RasNik, whose
measured values have shown a homogeneous expansion of the whole chamber,
overlayed by a shift and a rotation of the chamber middle with respect to the
outer part of the chamber. The established results of both methods are in
agreement. We present as well a model for the position-drifttime correction as
function of temperature.Comment: 4 pages, 12 figures, conferenc
A Cosmic Ray Measurement Facility for ATLAS Muon Chambers
Monitored Drift Tube (MDT) chambers will constitute the large majority of
precision detectors in the Muon Spectrometer of the ATLAS experiment at the
Large Hadron Collider at CERN. For commissioning and calibration of MDT
chambers, a Cosmic Ray Measurement Facility is in operation at Munich
University. The objectives of this facility are to test the chambers and
on-chamber electronics, to map the positions of the anode wires within the
chambers with the precision needed for standalone muon momentum measurement in
ATLAS, and to gain experience in the operation of the chambers and on-line
calibration procedures.
Until the start of muon chamber installation in ATLAS, 88 chambers built at
the Max Planck Institute for Physics in Munich have to be commissioned and
calibrated. With a data taking period of one day individual wire positions can
be measured with an accuracy of 8.3 micrometers in the chamber plane and 27
micrometers in the direction perpendicular to that plane.Comment: 14+1 pages, 11 figures, contributed paper to the EPS2003 conference,
Aache
Refined Analysis of the Electroweak Precision Data
We refine our recent analysis of the electroweak precision data at the \PZO\
pole by including the hadronic decay modes of the \PZO. Within the framework of
an effective Lagrangian we parametrize violation by the additional
process-specific parameters \De y_\nu, \De\yh, and \De\yb (for the
\PZO\nu\bar\nu, \PZO\Pq\bar\Pq, and \PZO\Pb\bar\Pb vertices) together
with the previously introduced parameters \De x, \De y, and \eps. We find
that a six-parameter analysis of the experimental data is indeed feasible, and
it is carried out in addition to a four-parameter fit for \De x, \De y,
\eps, and \De\yb only. We reemphasize that the experimental data have
become sensitive to the (combined) magnitude of the vertex corrections at the
\PWp\Pl\bar\nu (\PWm\nu\bar\Pl) and \PZO\Pl\bar\Pl vertices, \De y,
which is insensitive to the notion of the Higgs mechanism but dependent on the
non-Abelian, trilinear vector-boson coupling. Full explicit analytical results
for the standard one-loop predictions for the above-mentioned parameters are
given, and the leading two-loop top-quark effects are included. The analytic
formluae for the analysis of the experimental data in terms of the parameters
\De x, \De y etc.\ are presented in order to encourage experimentalists to
persue such an analysis by themselves with future data.Comment: 28 pages latex, 9 figures in uuencoded form, trivial misprint
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