5,736 research outputs found
Status report of the CERN microwave axion experiment
"Light Shining Through the Wall" experiments can probe the existence of
"axion like particles" through their weak coupling to photons. We have adapted
such an experiment to the microwave regime and constructed the table top
apparatus. This work presents an overview of the experimental setup and then
focuses on our latest measurement run and its results. By operating the
apparatus within a superconducting MRI magnet, competitive exclusion limits for
axion like particles to the first generation optical light shining through the
wall experiments have been achieved.Comment: Contributed to the 9th Patras Workshop on Axions, WIMPs and WISPs,
Mainz, June 24-28, 201
Status report of the CERN light shining through the wall experiment with microwave axions and related aspects
One way to proof or exclude the existence of axion like particles is a
microwave light shining through the wall experiment. In this publication we
will emphasize on the engineering aspects of such a setup, currently under
development at CERN. One critical point, to achieve meaningful results, is the
electromagnetic shielding between axion-emitter and -receiver cavity, which
needs to be in the order of 300 dB to improve over existing experimental
bounds. The RF leakage or electromagnetic crosstalk between both cavities must
be well controlled and quantified during the complete duration of the
experiment. A very narrow band (in the 10^-6 Hz range) homodyne detection
method is used to reveal the axion signal from background thermal noise. The
current status of the experiment is presented.Comment: Contributed to the "7th Patras Workshop on Axions, WIMPs and WISPs",
Mykonos June 26 - July 1 201
Status report and first results of the microwave LSW experiment at CERN
To detect or exclude the existence of hidden sector photons or axion like
particles, a table-top "microwaves shining through the wall" experiment has
been set up at CERN. An overview of the experimental layout is given, the
technical challenges involved are reviewed and the measurement procedure
including data-evaluation and its results to date are shown.Comment: Contributed to the 8th Patras Workshop on Axions, WIMPs and WISPs,
Chicago, July 18-22, 201
The measurement of heats of solution of high melting metallic systems in an electromagnetic levitation field
A method was tested for measuring the enthalpies of mixing of liquid metallic alloying systems, involving the combination of two samples in the electromagnetic field of an induction coil. The heat of solution is calculated from the pyrometrically measured temperature effect, the heat capacity of the alloy, and the heat content of the added sample. The usefulness of the method was tested experimentally with iron-copper and niobium-silicon systems. This method should be especially applicable to high-melting alloys, for which conventional measurements have failed
First results of the CERN Resonant WISP Search (CROWS)
The CERN Resonant WISP Search (CROWS) probes the existence of Weakly
Interacting Sub-eV Particles (WISPs) like axions or hidden sector photons. It
is based on the principle of an optical light shining through the wall
experiment, adapted to microwaves. Critical aspects of the experiment are
electromagnetic shielding, design and operation of low loss cavity resonators
and the detection of weak sinusoidal microwave signals. Lower bounds were set
on the coupling constant GeV for axion like
particles with a mass of eV. For hidden sector photons, lower
bounds were set for the coupling constant at a mass
of eV. For the latter we were probing a previously
unexplored region in the parameter space
Performance Analysis of Iterative Channel Estimation and Multiuser Detection in Multipath DS-CDMA Channels
This paper examines the performance of decision feedback based iterative
channel estimation and multiuser detection in channel coded aperiodic DS-CDMA
systems operating over multipath fading channels. First, explicit expressions
describing the performance of channel estimation and parallel interference
cancellation based multiuser detection are developed. These results are then
combined to characterize the evolution of the performance of a system that
iterates among channel estimation, multiuser detection and channel decoding.
Sufficient conditions for convergence of this system to a unique fixed point
are developed.Comment: To appear in the IEEE Transactions on Signal Processin
Initial Allocation Effects in Permit Markets with Bertrand Output Oligopoly
We analyse the efficiency effects of the initial permit allocation given to firms with market power in both permit and output market. We examine two models: a long- run model with endogenous technology and capacity choice, and a short-run model with fixed technology and capacity. In the long run, quantity pre-commitment with Bertrand competition can yield Cournot outcomes also under emissions trading. In the short run, Bertrand output competition reproduces the effects derived under Cournot competition, but displays higher pass-through profits. In a second-best setting of overallocation, a tighter emissions target tends to improve permit-market efficiency in the short run.Emissions trading, Initial permit allocation, Bertrand competition, EU ETS, Endogenous technology choice, Kreps and Scheinkman, Resource /Energy Economics and Policy, L13, Q28, D43,
Examining a reduced jet-medium coupling in Pb+Pb collisions at the Large Hadron Collider
Recent data on the nuclear modification factor of jet fragments in
2.76 ATeV Pb+Pb collisions at the Large Hadron Collider (LHC) indicate that the
jet-medium coupling in a Quark-Gluon Plasma (QGP) is reduced at LHC energies
and not compatible with the coupling deduced from data at the Relativistic
Hadron Collider (RHIC). We estimate the reduction factor from a combined fit to
the available data on and the elliptic flow
at ATeV over a transverse momentum
range 10-100 GeV and a broad impact parameter, b, range. We use a simple
analytic "polytrope" model () to investigate
the dynamical jet-energy loss model dependence. Varying a=0-1 interpolates
between weakly-coupled and strongly-coupled models of jet-energy dependence
while z=0-2 covers a wide range of possible jet-path dependencies from elastic
and radiative to holographic string mechanisms. Our fit to LHC data indicates
an approximate 40% reduction of the coupling from RHIC to LHC and
excludes energy-loss models characterized by a jet-energy exponent with a>1/3.
In particular, the rapid rise of with >10 GeV combined with the
slow variation of the asymptotic at the LHC rules out popular
exponential geometric optics models (a=1). The LHC data are compatible with
pQCD-like energy-loss models where the jet-medium coupling is
reduced by approximately 10% between RHIC and LHC.Comment: 10 pages, 7 figures, version published in Physical Review
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