293 research outputs found
Gain Stabilization of a Submillimeter SIS Heterodyne Receiver
We have designed a system to stabilize the gain of a submillimeter heterodyne
receiver against thermal fluctuations of the mixing element. In the most
sensitive heterodyne receivers, the mixer is usually cooled to 4 K using a
closed-cycle cryocooler, which can introduce ~1% fluctuations in the physical
temperature of the receiver components. We compensate for the resulting mixer
conversion gain fluctuations by monitoring the physical temperature of the
mixer and adjusting the gain of the intermediate frequency (IF) amplifier that
immediately follows the mixer. This IF power stabilization scheme, developed
for use at the Submillimeter Array (SMA), a submillimeter interferometer
telescope on Mauna Kea in Hawaii, routinely achieves a receiver gain stability
of 1 part in 6,000 (rms to mean). This is an order of magnitude improvement
over the typical uncorrected stability of 1 part in a few hundred. Our gain
stabilization scheme is a useful addition to SIS heterodyne receivers that are
cooled using closed-cycle cryocoolers in which the 4 K temperature fluctuations
tend to be the leading cause of IF power fluctuations.Comment: 7 pages, 6 figures accepted to IEEE Transactions on Microwave Theory
and Technique
Dark Matter Time Projection Chamber: Recent R&D Results
The Dark Matter Time Projection Chamber collaboration recently reported a dark matter limit obtained with a 10 liter time projection chamber filled with CF4 gas. The 10 liter detector was capable of 2D tracking (perpendicular to the drift direction) and 2D fiducialization, and only used information from two CCD cameras when identifying tracks and rejecting backgrounds. Since that time, the collaboration has explored the potential benefits of photomultiplier tube and electronic charge readout to achieve 3D tracking, and particle identification for background rejection. The latest results of this effort is described here
Detection Prospects for Majorana Fermion WIMPless Dark Matter
We consider both velocity-dependent and velocity-independent contributions to
spin-dependent (SD) and spin-independent (SI) nuclear scattering (including
one-loop corrections) of WIMPless dark matter, in the case where the dark
matter candidate is a Majorana fermion. We find that spin-independent
scattering arises only from the mixing of exotic squarks, or from
velocity-dependent terms. Nevertheless (and contrary to the case of MSSM
neutralino WIMPs), we find a class of models which cannot be detected through
SI scattering, but can be detected at IceCube/DeepCore through SD scattering.
We study the detection prospects for both SI and SD detection strategies for a
large range of Majorana fermion WIMPless model parameters.Comment: 14 pages, 3 figures. v2: updated to match published versio
DMTPC: A dark matter detector with directional sensitivity
By correlating nuclear recoil directions with the Earth's direction of motion
through the Galaxy, a directional dark matter detector can unambiguously detect
Weakly Interacting Massive Particles (WIMPs), even in the presence of
backgrounds. Here, we describe the Dark Matter Time-Projection Chamber (DMTPC)
detector, a TPC filled with CF4 gas at low pressure (0.1 atm). Using this
detector, we have measured the vector direction (head-tail) of nuclear recoils
down to energies of 100 keV with an angular resolution of <15 degrees. To study
our detector backgrounds, we have operated in a basement laboratory on the MIT
campus for several months. We are currently building a new, high-radiopurity
detector for deployment underground at the Waste Isolation Pilot Plant facility
in New Mexico.Comment: 4 pages, 2 figures, proceedings for the CIPANP 2009 conference, May
26-31, 200
Background Rejection in the DMTPC Dark Matter Search Using Charge Signals
The Dark Matter Time Projection Chamber (DMTPC) collaboration is developing
low-pressure gas TPC detectors for measuring WIMP-nucleon interactions. Optical
readout with CCD cameras allows for the detection for the daily modulation in
the direction of the dark matter wind, while several charge readout channels
allow for the measurement of additional recoil properties. In this article, we
show that the addition of the charge readout analysis to the CCD allows us too
obtain a statistics-limited 90% C.L. upper limit on the rejection factor
of for recoils with energies between 40 and 200
keV. In addition, requiring coincidence between charge signals
and light in the CCD reduces CCD-specific backgrounds by more than two orders
of magnitude.Comment: 8 pages, 6 figures. For proceedings of DPF 2011 conferenc
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