1,082 research outputs found
APEX: A Prime EXperiment at Jefferson Lab
APEX is an experiment at Thomas Jefferson National Accelerator Facility
(JLab) in Virginia, USA, that searches for a new gauge boson () with
sub-GeV mass and coupling to ordinary matter of . Electrons impinge upon a fixed target of high-Z material. An
is produced via a process analogous to photon bremsstrahlung,
decaying to an pair. A test run was held in July of 2010, covering
= 175 to 250 MeV and couplings g^\prime/e \; \textgreater \;
10^{-3}. A full run is approved and will cover 65 to 525
MeV and g^\prime/e \; \textgreater \; 2.3 \times10^{-4}.Comment: Contributed to the 8th Patras Workshop on Axions, WIMPs and WISPs,
Chicago, July 18-22, 2012. 4 pages, 4 figure
Generation of adaptive coordinates and their use in the Fourier Modal Method
We present an improvement of the standard Fourier Modal Method (FMM) for the analysis of lamellar gratings that is based on the use of automatically generated adaptive coordinates for arbitrarily shaped material profiles in the lateral plane of periodicity. This allows for an accurate resolution of small geometric features and/or large material contrasts within the unit. For dielectric gratings, we obtain considerable convergence accelerations. Similarly, for metallic gratings, our approach allows efficient and accurate computations of transmittance and reflectance coefficients into various Bragg orders, the spectral positions of Rayleigh anomalies, and field enhancement values within the grating structures
Jet diffuser for simulating ram conditions on a turbojet-engine static test stand
A jet diffuser for simulating flight or ram conditions on a turbojet-engine static test stand was designed and investigated. The diffuser utilizes the kinetic energy of the jet from a turbojet engine to reduce the discharge pressure at the exhaust nozzle and thereby provides simulated ram-pressure ratios across the engine. The engine exhaust nozzle discharges into an exhaust chamber (flexibly sealed to the tail pipe), which is connected to a diffuser by a bell-shaped nozzle. The pressure in the exhaust chamber is controlled independently of engine speed by a variable-area shutter at the diffuser discharge. The jet diffuser simulated ram-pressure ratios from 0.95 to 2.2 at various simulated pressure altitudes for a range of engine speeds from 85 to 100 percent of maximum rpm. Agreement of data obtained with and without the jet diffuser for a ram-pressure ratio of 1.0 indicated that the presence of the diffuser did not interfere with the flow through the engine exhaust-nozzle outlet
An Electron Fixed Target Experiment to Search for a New Vector Boson A' Decaying to e+e-
We describe an experiment to search for a new vector boson A' with weak
coupling alpha' > 6 x 10^{-8} alpha to electrons (alpha=e^2/4pi) in the mass
range 65 MeV < m_A' < 550 MeV. New vector bosons with such small couplings
arise naturally from a small kinetic mixing of the "dark photon" A' with the
photon -- one of the very few ways in which new forces can couple to the
Standard Model -- and have received considerable attention as an explanation of
various dark matter related anomalies. A' bosons are produced by radiation off
an electron beam, and could appear as narrow resonances with small production
cross-section in the trident e+e- spectrum. We summarize the experimental
approach described in a proposal submitted to Jefferson Laboratory's PAC35,
PR-10-009. This experiment, the A' Experiment (APEX), uses the electron beam of
the Continuous Electron Beam Accelerator Facility at Jefferson Laboratory
(CEBAF) at energies of ~1-4 GeV incident on 0.5-10% radiation length Tungsten
wire mesh targets, and measures the resulting e+e- pairs to search for the A'
using the High Resolution Spectrometer and the septum magnet in Hall A. With a
~1 month run, APEX will achieve very good sensitivity because the statistics of
e+e- pairs will be ~10,000 times larger in the explored mass range than any
previous search for the A' boson. These statistics and the excellent mass
resolution of the spectrometers allow sensitivity to alpha'/alpha one to three
orders of magnitude below current limits, in a region of parameter space of
great theoretical and phenomenological interest. Similar experiments could also
be performed at other facilities, such as the Mainz Microtron.Comment: 19 pages, 12 figures, 2 table
Two Loop R-Symmetry Breaking
We analyze two loop quantum corrections for pseudomoduli in O'Raifeartaigh
like models. We argue that R-symmetry can be spontaneously broken at two loop
in non supersymmetric vacua. We provide a basic example with this property. We
discuss on phenomenological applications.Comment: 13 pages, 5 figures, JHEP3.cls, reference adde
Testing SUSY
If SUSY provides a solution to the hierarchy problem then supersymmetric
states should not be too heavy. This requirement is quantified by a fine tuning
measure that provides a quantitative test of SUSY as a solution to the
hierarchy problem. The measure is useful in correlating the impact of the
various experimental measurements relevant to the search for supersymmetry and
also in identifying the most sensitive measurements for testing SUSY. In this
paper we apply the measure to the CMSSM, computing it to two-loop order and
taking account of current experimental limits and the constraint on dark matter
abundance. Using this we determine the present limits on the CMSSM parameter
space and identify the measurements at the LHC that are most significant in
covering the remaining parameter space. Without imposing the LEP Higgs mass
bound we show that the smallest fine tuning (1:13) consistent with a relic
density within the WMAP bound corresponds to a Higgs mass of 1142 GeV.
Fine tuning rises rapidly for heavier Higgs.Comment: 12 pages, 7 figures; references added, figures updated for extended
parameter space sca
Decays of metastable vacua in SQCD
The decay rates of metastable SQCD vacua in ISS-type models, both towards
supersymmetric vacua as well as towards other nonsupersymmetric configurations
arising in theories with elementary spectators, are estimated numerically in
the semiclassical approximation by computing the corresponding multifield
bounce configurations. The scaling of the bounce action with respect to the
most relevant dimensionless couplings and ratios of scales is analyzed. In the
case of the decays towards the susy vacua generated by nonperturbative effects,
the results confirm previous analytical estimations of this scaling, obtained
by assuming a triangular potential barrier. The decay rates towards susy vacua
generated by R-symmetry breaking interactions turn out to be more than
sufficiently suppressed for the phenomenologically relevant parameter range,
and their behavior in this regime differs from analytic estimations valid for
parametrically small scale ratios. It is also shown that in models with
spectator fields, even though the decays towards vacua involving nonzero
spectator VEVs don't have a strong parametric dependence on the scale ratios,
the ISS vacuum can still be made long-lived in the presence of R-symmetry
breaking interactions.Comment: 22 pages, 7 figure
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