1,250 research outputs found
XAX: a multi-ton, multi-target detection system for dark matter, double beta decay and pp solar neutrinos
A multi-target detection system XAX, comprising concentric 10 ton targets of
136Xe and 129/131Xe, together with a geometrically similar or larger target of
liquid Ar, is described. Each is configured as a two-phase
scintillation/ionization TPC detector, enhanced by a full 4pi array of
ultra-low radioactivity Quartz Photon Intensifying Detectors (QUPIDs) replacing
the conventional photomultipliers for detection of scintillation light. It is
shown that background levels in XAX can be reduced to the level required for
dark matter particle (WIMP) mass measurement at a 10^-10 pb WIMP-nucleon cross
section, with single-event sensitivity below 10^-11 pb. The use of multiple
target elements allows for confirmation of the A^2 dependence of a coherent
cross section, and the different Xe isotopes provide information on the
spin-dependence of the dark matter interaction. The event rates observed by Xe
and Ar would modulate annually with opposite phases from each other for WIMP
mass >~100 GeV/c^2. The large target mass of 136Xe and high degree of
background reduction allow neutrinoless double beta decay to be observed with
lifetimes of 10^27-10^28 years, corresponding to the Majorana neutrino mass
range 0.01-0.1 eV, the most likely range from observed neutrino mass
differences. The use of a 136Xe-depleted 129/131Xe target will also allow
measurement of the pp solar neutrino spectrum to a precision of 1-2%.Comment: 16 pages with 17 figure
Magnetic Cycles in a Convective Dynamo Simulation of a Young Solar-type Star
Young solar-type stars rotate rapidly and many are magnetically active; some
undergo magnetic cycles similar to the 22-year solar activity cycle. We conduct
simulations of dynamo action in rapidly rotating suns with the 3D MHD anelastic
spherical harmonic (ASH) code to explore dynamo action achieved in the
convective envelope of a solar-type star rotating at 5 times the current solar
rotation rate. Striking global-scale magnetic wreaths appear in the midst of
the turbulent convection zone and show rich time-dependence. The dynamo
exhibits cyclic activity and undergoes quasi-periodic polarity reversals where
both the global-scale poloidal and toroidal fields change in sense on a roughly
1500 day time scale. These magnetic activity patterns emerge spontaneously from
the turbulent flow and are more organized temporally and spatially than those
realized in our previous simulations of the solar dynamo. We assess in detail
the competing processes of magnetic field creation and destruction within our
simulations that contribute to the global-scale reversals. We find that the
mean toroidal fields are built primarily through an -effect, while the
mean poloidal fields are built by turbulent correlations which are not
necessarily well represented by a simple -effect. During a reversal the
magnetic wreaths propagate towards the polar regions, and this appears to arise
from a poleward propagating dynamo wave. The primary response in the convective
flows involves the axisymmetric differential rotation which shows variations
associated with the poleward propagating magnetic wreaths. In the Sun, similar
patterns are observed in the poleward branch of the torsional oscillations, and
these may represent poleward propagating magnetic fields deep below the solar
surface. [abridged]Comment: 20 pages, 14 figures, emulateapj format; accepted for publication in
ApJ. Expanded and published version of sections 5-6 from
http://arxiv.org/abs/0906.240
Persistent Magnetic Wreaths in a Rapidly Rotating Sun
When our Sun was young it rotated much more rapidly than now. Observations of
young, rapidly rotating stars indicate that many possess substantial magnetic
activity and strong axisymmetric magnetic fields. We conduct simulations of
dynamo action in rapidly rotating suns with the 3-D MHD anelastic spherical
harmonic (ASH) code to explore the complex coupling between rotation,
convection and magnetism. Here we study dynamo action realized in the bulk of
the convection zone for a system rotating at three times the current solar
rotation rate. We find that substantial organized global-scale magnetic fields
are achieved by dynamo action in this system. Striking wreaths of magnetism are
built in the midst of the convection zone, coexisting with the turbulent
convection. This is a surprise, for it has been widely believed that such
magnetic structures should be disrupted by magnetic buoyancy or turbulent
pumping. Thus, many solar dynamo theories have suggested that a tachocline of
penetration and shear at the base of the convection zone is a crucial
ingredient for organized dynamo action, whereas these simulations do not
include such tachoclines. We examine how these persistent magnetic wreaths are
maintained by dynamo processes and explore whether a classical mean-field
-effect explains the regeneration of poloidal field.Comment: 17 pages, 9 figures, 1 appendix, emulateapj format; published version
of sections 3-4, 7 and appendix from arXiv:0906.240
The role of -induced reactions on lead and iron in neutrino detectors
We have calculated cross sections and branching ratios for neutrino induced
reactions on ^{208}Pb and ^{56}Fe for various supernova and
accelerator-relevant neutrino spectra. This was motivated by the facts that
lead and iron will be used on one hand as target materials in future neutrino
detectors, on the other hand have been and are still used as shielding
materials in accelerator-based experiments. In particular we study the
inclusive ^{56}^{56}Co and ^{208}^{208}Bi cross
sections and calculate the neutron energy spectra following the decay of the
daughter nuclei. These reactions give a potential background signal in the
KARMEN and LSND experiment and are discussed as a detection scheme for
supernova neutrinos in the proposed OMNIS and LAND detectors. We also study the
neutron-emission following the neutrino-induced neutral-current excitation of
^{56}Fe and ^{208}Pb.Comment: 23 pages (including 7 figures
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
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
Dark Matter Results from 100 Live Days of XENON100 Data
We present results from the direct search for dark matter with the XENON100
detector, installed underground at the Laboratori Nazionali del Gran Sasso of
INFN, Italy. XENON100 is a two-phase time projection chamber with a 62 kg
liquid xenon target. Interaction vertex reconstruction in three dimensions with
millimeter precision allows to select only the innermost 48 kg as ultra-low
background fiducial target. In 100.9 live days of data, acquired between
January and June 2010, no evidence for dark matter is found. Three candidate
events were observed in a pre-defined signal region with an expected background
of 1.8 +/- 0.6 events. This leads to the most stringent limit on dark matter
interactions today, excluding spin-independent elastic WIMP-nucleon scattering
cross-sections above 7.0x10^-45 cm^2 for a WIMP mass of 50 GeV/c^2 at 90%
confidence level.Comment: 5 pages, 5 figures; matches accepted versio
Implications on Inelastic Dark Matter from 100 Live Days of XENON100 Data
The XENON100 experiment has recently completed a dark matter run with 100.9
live-days of data, taken from January to June 2010. Events in a 48kg fiducial
volume in the energy range between 8.4 and 44.6 keVnr have been analyzed. A
total of three events have been found in the predefined signal region,
compatible with the background prediction of (1.8 \pm 0.6) events. Based on
this analysis we present limits on the WIMP-nucleon cross section for inelastic
dark matter. With the present data we are able to rule out the explanation for
the observed DAMA/LIBRA modulation as being due to inelastic dark matter
scattering off iodine at a 90% confidence level.Comment: 3 pages, 3 figure
Material screening and selection for XENON100
Results of the extensive radioactivity screening campaign to identify
materials for the construction of XENON100 are reported. This Dark Matter
search experiment is operated underground at Laboratori Nazionali del Gran
Sasso (LNGS), Italy. Several ultra sensitive High Purity Germanium detectors
(HPGe) have been used for gamma ray spectrometry. Mass spectrometry has been
applied for a few low mass plastic samples. Detailed tables with the
radioactive contaminations of all screened samples are presented, together with
the implications for XENON100.Comment: 8 pages, 1 figur
Comment on "On the subtleties of searching for dark matter with liquid xenon detectors"
In a recent manuscript (arXiv:1208.5046) Peter Sorensen claims that
XENON100's upper limits on spin-independent WIMP-nucleon cross sections for
WIMP masses below 10 GeV "may be understated by one order of magnitude or
more". Having performed a similar, though more detailed analysis prior to the
submission of our new result (arXiv:1207.5988), we do not confirm these
findings. We point out the rationale for not considering the described effect
in our final analysis and list several potential problems with his study.Comment: 3 pages, no figure
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