923 research outputs found
Characterization of the Hamamatsu R11410-10 3-Inch Photomultiplier Tube for Liquid Xenon Dark Matter Direct Detection Experiments
To satisfy the requirements of the next generation of dark matter detectors
based on the dual phase TPC, Hamamatsu, in close collaboration with UCLA, has
developed the R11410-10 photomultipler tube. In this work, we present the
detailed tests performed on this device. High QE (>30%) accompanied by a low
dark count rate (50 Hz at 0.3 PE) and high gain (10^7) with good single PE
resolution have been observed. A comprehensive screening measurement campaign
is ongoing while the manufacturer quotes a radioactivity of 20 mBq/PMT. These
characteristics show the R11410-10 to be particularly suitable for the
forthcoming zero background liquid xenon detectors.Comment: 19 pages, 18 figure
Characterization of the QUartz Photon Intensifying Detector (QUPID) for Noble Liquid Detectors
Dark Matter and Double Beta Decay experiments require extremely low
radioactivity within the detector materials. For this purpose, the University
of California, Los Angeles and Hamamatsu Photonics have developed the QUartz
Photon Intensifying Detector (QUPID), an ultra-low background photodetector
based on the Hybrid Avalanche Photo Diode (HAPD) and entirely made of
ultraclean synthetic fused silica. In this work we present the basic concept of
the QUPID and the testing measurements on QUPIDs from the first production
line. Screening of radioactivity at the Gator facility in the Laboratori
Nazionali del Gran Sasso has shown that the QUPIDs safely fulfill the low
radioactive contamination requirements for the next generation zero background
experiments set by Monte Carlo simulations. The quantum efficiency of the QUPID
at room temperature is > 30% at the xenon scintillation wavelength. At low
temperatures, the QUPID shows a leakage current less than 1 nA and a global
gain of 10^5. In these conditions, the photocathode and the anode show > 95%
linearity up to 1 uA for the cathode and 3 mA for the anode. The photocathode
and collection efficiency are uniform to 80% over the entire surface. In
parallel with single photon counting capabilities, the QUPIDs have a good
timing response: 1.8 +/- 0.1 ns rise time, 2.5 +/- 0.2 ns fall time, 4.20 +/-
0.05 ns pulse width, and 160 +/- 30 ps transit time spread. The QUPIDs have
also been tested in a liquid xenon environment, and scintillation light from
57Co and 210Po radioactive sources were observed.Comment: 15 pages, 22 figure
Lepton Flavor Violation in the Two Higgs Doublet Model type III
We consider the Two Higgs Doublet Model (2HDM) of type III which leads to
Flavour Changing Neutral Currents (FCNC) at tree level in the leptonic sector.
In the framework of this model we can have, in principle, two situations: the
case (a) when both doublets acquire a vacuum expectation value different from
zero and the case (b) when only one of them is not zero. In addition, we show
that we can make two types of rotations for the flavor mixing matrices which
generates four types of lagrangians, with the rotation of type I we recover the
case (b) from the case (a) in the limit , and with the
rotation of type II we obtain the case (b) from (a) in the limit Moreover, two of the four possible lagrangians correspond to the models
of types I and II plus Flavor Changing (FC) interactions. The analitical
expressions of the partial lepton number violating widths and are derived for the cases (a) and (b) and both
types of rotations.In all cases these widths go asymptotically to zero in
the decoupling limit for all Higgses. We present from our analysis upper bounds
for the flavour changing transition and we show that such bounds
are sensitive to the VEV structure and the type of rotation utilized.Comment: 7 pages RevTeX4, 4 figures postscript, new section added and some new
reference
Studies of a three-stage dark matter and neutrino observatory based on multi-ton combinations of liquid xenon and liquid argon detectors
We study a three stage dark matter and neutrino observatory based on
multi-ton two-phase liquid Xe and Ar detectors with sufficiently low
backgrounds to be sensitive to WIMP dark matter interaction cross sections down
to 10E-47 cm^2, and to provide both identification and two independent
measurements of the WIMP mass through the use of the two target elements in a
5:1 mass ratio, giving an expected similarity of event numbers. The same
detection systems will also allow measurement of the pp solar neutrino
spectrum, the neutrino flux and temperature from a Galactic supernova, and
neutrinoless double beta decay of 136Xe to the lifetime level of 10E27 - 10E28
y corresponding to the Majorana mass predicted from current neutrino
oscillation data. The proposed scheme would be operated in three stages G2, G3,
G4, beginning with fiducial masses 1-ton Xe + 5-ton Ar (G2), progressing to
10-ton Xe + 50-ton Ar (G3) then, dependent on results and performance of the
latter, expandable to 100-ton Xe + 500-ton Ar (G4). This method of scale-up
offers the advantage of utilizing the Ar vessel and ancillary systems of one
stage for the Xe detector of the succeeding stage, requiring only one new
detector vessel at each stage. Simulations show the feasibility of reducing or
rejecting all external and internal background levels to a level <1 events per
year for each succeeding mass level, by utilizing an increasing outer thickness
of target material as self-shielding. The system would, with increasing mass
scale, become increasingly sensitive to annual signal modulation, the agreement
of Xe and Ar results confirming the Galactic origin of the signal. Dark matter
sensitivities for spin-dependent and inelastic interactions are also included,
and we conclude with a discussion of possible further gains from the use of
Xe/Ar mixtures
Monte-Carlo Simulation for an Aerogel Cherenkov Counter
We have developed a Monte-Carlo simulation code for an aerogel \v Cerenkov
Counter which is operated under a strong magnetic field such as 1.5T. This code
consists of two parts: photon transportation inside aerogel tiles, and
one-dimensional amplification in a fine-mesh photomultiplier tube. It simulates
the output photoelectron yields as accurately as 5% with only a single free
parameter. This code is applied to simulations for a B-Factory
particle-identification system.Comment: 40 pages, latex(article), 19 figure
Rare Kaon Decays
The current status of rare kaon decay experiments is reviewed. New limits in
the search for Lepton Flavor Violation are discussed, as are new measurements
of the CKM matrix.Comment: 8 pages, 3 figures, LaTeX, presented at the 3rd International
Conference on B Phyiscs and CP Violation, Taipei December 3-7, 199
An Action-Based Approach to Presence: Foundations and Methods
This chapter presents an action-based approach to presence. It starts by briefly describing the theoretical and empirical foundations of this approach, formalized into three key notions of place/space, action and mediation. In the light of these notions, some common assumptions about presence are then questioned: assuming a neat distinction between virtual and real environments, taking for granted the contours of the mediated environment and considering presence as a purely personal state. Some possible research topics opened up by adopting action as a unit of analysis are illustrated. Finally, a case study on driving as a form of mediated presence is discussed, to provocatively illustrate the flexibility of this approach as a unified framework for presence in digital and physical environment
First Dark Matter Results from the XENON100 Experiment
The XENON100 experiment, in operation at the Laboratori Nazionali del Gran
Sasso in Italy, is designed to search for dark matter WIMPs scattering off 62
kg of liquid xenon in an ultra-low background dual-phase time projection
chamber. In this letter, we present first dark matter results from the analysis
of 11.17 live days of non-blind data, acquired in October and November 2009. In
the selected fiducial target of 40 kg, and within the pre-defined signal
region, we observe no events and hence exclude spin-independent WIMP-nucleon
elastic scattering cross-sections above 3.4 x 10^-44 cm^2 for 55 GeV/c^2 WIMPs
at 90% confidence level. Below 20 GeV/c^2, this result constrains the
interpretation of the CoGeNT and DAMA signals as being due to spin-independent,
elastic, light mass WIMP interactions.Comment: 5 pages, 5 figures. Matches published versio
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