240 research outputs found
Solar system constraints on the Dvali-Gabadadze-Porrati braneworld theory of gravity
A number of proposals have been put forward to account for the observed
accelerating expansion of the Universe through modifications of gravity. One
specific scenario, Dvali-Gabadadze-Porrati (DGP) gravity, gives rise to a
potentially observable anomaly in the solar system: all planets would exhibit a
common anomalous precession, dw/dt, in excess of the prediction of General
Relativity. We have used the Planetary Ephemeris Program (PEP) along with
planetary radar and radio tracking data to set a constraint of |dw/dt| < 0.02
arcseconds per century on the presence of any such common precession. This
sensitivity falls short of that needed to detect the estimated universal
precession of |dw/dt| = 5e-4 arcseconds per century expected in the DGP
scenario. We discuss the fact that ranging data between objects that orbit in a
common plane cannot constrain the DGP scenario. It is only through the relative
inclinations of the planetary orbital planes that solar system ranging data
have sensitivity to the DGP-like effect of universal precession. In addition,
we illustrate the importance of performing a numerical evaluation of the
sensitivity of the data set and model to any perturbative precession.Comment: 9 pages, 2 figures, accepted for publication in Phys. Rev.
APOLLO: the Apache Point Observatory Lunar Laser-ranging Operation: Instrument Description and First Detections
A next-generation lunar laser ranging apparatus using the 3.5 m telescope at
the Apache Point Observatory in southern New Mexico has begun science
operation. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation)
has achieved one-millimeter range precision to the moon which should lead to
approximately one-order-of-magnitude improvements in the precision of several
tests of fundamental properties of gravity. We briefly motivate the scientific
goals, and then give a detailed discussion of the APOLLO instrumentation.Comment: 37 pages; 10 figures; 1 table: accepted for publication in PAS
An absolute calibration system for millimeter-accuracy APOLLO measurements
Lunar laser ranging provides a number of leading experimental tests of
gravitation -- important in our quest to unify General Relativity and the
Standard Model of physics. The Apache Point Observatory Lunar Laser-ranging
Operation (APOLLO) has for years achieved median range precision at the ~2 mm
level. Yet residuals in model-measurement comparisons are an order-of-magnitude
larger, raising the question of whether the ranging data are not nearly as
accurate as they are precise, or if the models are incomplete or
ill-conditioned. This paper describes a new absolute calibration system (ACS)
intended both as a tool for exposing and eliminating sources of systematic
error, and also as a means to directly calibrate ranging data in-situ. The
system consists of a high-repetition-rate (80 MHz) laser emitting short (< 10
ps) pulses that are locked to a cesium clock. In essence, the ACS delivers
photons to the APOLLO detector at exquisitely well-defined time intervals as a
"truth" input against which APOLLO's timing performance may be judged and
corrected. Preliminary analysis indicates no inaccuracies in APOLLO data beyond
the ~3 mm level, suggesting that historical APOLLO data are of high quality and
motivating continued work on model capabilities. The ACS provides the means to
deliver APOLLO data both accurate and precise below the 2 mm level.Comment: 21 pages, 10 figures, submitted to Classical and Quantum Gravit
Performance of 20:1 multiplexer for large area charge readouts in directional dark matter TPC detectors
More target mass is required in current TPC based directional dark matter detectors for improved detector sensitivity. This can be achieved by scaling up the detector volumes, but this results in the need for more analogue signal channels. A possible solution to reducing the overall cost of the charge readout electronics is to multiplex the signal readout channels. Here, we present work on an expanded LMH6574 multiplexer system with a capability of reducing the number of readouts in such TPC detectors by a factor of 20. Results indicate that the important charge distribution asymmetry along an ionization track is retained after multiplexed signals are demultiplexed
Epstein-Barr virus-transformed pro-B cells are prone to illegitimate recombination between the switch region of the mu chain gene and other chromosomes.
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
Reducing DRIFT backgrounds with a submicron aluminized-mylar cathode
Background events in the DRIFT-IId dark matter detector, mimicking potential WIMP signals, are predominantly caused by alpha decays on the central cathode in which the alpha particle is completely or partially absorbed by the cathode material. We installed a View the MathML source thick aluminized-mylar cathode as a way to reduce the probability of producing these backgrounds. We study three generations of cathode (wire, thin-film, and radiologically clean thin-film) with a focus on the ratio of background events to alpha decays. Two independent methods of measuring the absolute alpha decay rate are used to ensure an accurate result, and agree to within 10%. Using alpha range spectroscopy, we measure the radiologically cleanest cathode version to have a contamination of 3.3±0.1 ppt 234U and 73±2 ppb 238U. This cathode reduces the probability of producing an RPR from an alpha decay by a factor of 70±20 compared to the original stainless steel wire cathode. First results are presented from a texturized version of the cathode, intended to be even more transparent to alpha particles. These efforts, along with other background reduction measures, have resulted in a drop in the observed background rate from 500/day to 1/day. With the recent implementation of full-volume fiducialization, these remaining background events are identified, allowing for background-free operation
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 CF[subscript 4] 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
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