57 research outputs found
Identification of the electroelastic coupling from full multi-physical fields measured at the micrometre scale
Lowering the radioactivity of the photomultiplier tubes for the XENON1T dark matter experiment
The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410
has been developed by Hamamatsu for dark matter direct detection experiments
using liquid xenon as the target material. We present the results from the
joint effort between the XENON collaboration and the Hamamatsu company to
produce a highly radio-pure photosensor (version R11410-21) for the XENON1T
dark matter experiment. After introducing the photosensor and its components,
we show the methods and results of the radioactive contamination measurements
of the individual materials employed in the photomultiplier production. We then
discuss the adopted strategies to reduce the radioactivity of the various PMT
versions. Finally, we detail the results from screening 216 tubes with
ultra-low background germanium detectors, as well as their implications for the
expected electronic and nuclear recoil background of the XENON1T experiment.Comment: 10 pages, 5 figure
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
Search for Event Rate Modulation in XENON100 Electronic Recoil Data
We have searched for periodic variations of the electronic recoil event rate
in the (2-6) keV energy range recorded between February 2011 and March 2012
with the XENON100 detector, adding up to 224.6 live days in total. Following a
detailed study to establish the stability of the detector and its background
contributions during this run, we performed an un-binned profile likelihood
analysis to identify any periodicity up to 500 days. We find a global
significance of less than 1 sigma for all periods suggesting no statistically
significant modulation in the data. While the local significance for an annual
modulation is 2.8 sigma, the analysis of a multiple-scatter control sample and
the phase of the modulation disfavor a dark matter interpretation. The
DAMA/LIBRA annual modulation interpreted as a dark matter signature with
axial-vector coupling of WIMPs to electrons is excluded at 4.8 sigma.Comment: 6 pages, 4 figure
Removing krypton from xenon by cryogenic distillation to the ppq level
The XENON1T experiment aims for the direct detection of dark matter in a
cryostat filled with 3.3 tons of liquid xenon. In order to achieve the desired
sensitivity, the background induced by radioactive decays inside the detector
has to be sufficiently low. One major contributor is the -emitter
Kr which is an intrinsic contamination of the xenon. For the XENON1T
experiment a concentration of natural krypton in xenon Kr/Xe < 200
ppq (parts per quadrillion, 1 ppq = 10 mol/mol) is required. In this
work, the design of a novel cryogenic distillation column using the common
McCabe-Thiele approach is described. The system demonstrated a krypton
reduction factor of 6.410 with thermodynamic stability at process
speeds above 3 kg/h. The resulting concentration of Kr/Xe < 26 ppq
is the lowest ever achieved, almost one order of magnitude below the
requirements for XENON1T and even sufficient for future dark matter experiments
using liquid xenon, such as XENONnT and DARWIN
Search for Two-Neutrino Double Electron Capture of Xe with XENON100
Two-neutrino double electron capture is a rare nuclear decay where two
electrons are simultaneously captured from the atomic shell. For Xe
this process has not yet been observed and its detection would provide a new
reference for nuclear matrix element calculations. We have conducted a search
for two-neutrino double electron capture from the K-shell of Xe using
7636 kgd of data from the XENON100 dark matter detector. Using a
Bayesian analysis we observed no significant excess above background, leading
to a lower 90 % credibility limit on the half-life
yr. We also evaluated the sensitivity of the XENON1T experiment, which is
currently being commissioned, and find a sensitivity of
yr after an exposure of 2 tyr.Comment: 6 pages, 4 figure
ULF geomagnetic pulsations at different latitudes in Antarctica
We present a study aimed to characterize the ULF (1–100 mHz) geomagnetic pulsation activity in the polar cap at different latitudes. We used magnetic measurements obtained through 2005–2007 in Antarctica, at Dome C (89&deg; S corrected geomagnetic latitude) and at Terra Nova Bay (80&deg; S corrected geomagnetic latitude). The results indicate a solar wind control of the wave activity, more important at larger distances from the cusp, as well as a significant role of the local ionospheric conditions. The different position of the two stations, with respect to the cusp and closed field lines, is responsible for the observed different pulsation characteristics. At Terra Nova Bay, due to the approaching of the station to the cusp and closed field lines in the daytime, the ULF power is characterized by a maximum around noon; daytime pulsation events in the Pc5 frequency band are related to the fundamental field line resonances occurring at lower latitudes, while higher harmonics of the fundamental may account for the characteristics of Pc3–4 pulsations. In the nighttime, at Pc3 frequencies, the results suggest waves propagating sunward, possibly due to the transmission of upstream waves from the magnetosheath via the magnetotail lobes. At Dome C, near the geomagnetic pole and very far from closed field lines, the ULF power in any frequency band only shows an enhancement in the postmidnight sector, more pronounced for Pc3 pulsations. The ULF activity appears to be driven by processes occurring in the magnetotail: in particular, nighttime Pc3 pulsation events may be originated from upstream wave penetration through the magnetotail lobes
Dark Matter Results from 225 Live Days of XENON100 Data
We report on a search for particle dark matter with the XENON100 experiment,
operated at the Laboratori Nazionali del Gran Sasso (LNGS) for 13 months during
2011 and 2012. XENON100 features an ultra-low electromagnetic background of
(5.3 \pm 0.6) \times 10^-3 events (kg day keVee)^-1 in the energy region of
interest. A blind analysis of 224.6 live days \times 34 kg exposure has yielded
no evidence for dark matter interactions. The two candidate events observed in
the pre-defined nuclear recoil energy range of 6.6-30.5 keVnr are consistent
with the background expectation of (1.0 \pm 0.2) events. A Profile Likelihood
analysis using a 6.6-43.3 keVnr energy range sets the most stringent limit on
the spin-independent elastic WIMP-nucleon scattering cross section for WIMP
masses above 8 GeV/c^2, with a minimum of 2 \times 10^-45 cm^2 at 55 GeV/c^2
and 90% confidence level.Comment: 6 pages, 5 figures. Matches version accepted by PRL. Includes limits
up to 10 TeV/c^2, published as supplementary material:
http://prl.aps.org/supplemental/PRL/v109/i18/e181301 Please cite high mass
limits as "Phys. Rev. Lett. 109, 181301 (2012), online supplementary
material.
Search for Two-Neutrino Double Electron Capture of <sup>124</sup>Xe with XENON100
Two-neutrino double electron capture is a rare nuclear decay where two electrons are simultaneously captured from the atomic shell. For Xe this process has not yet been observed and its detection would provide a new reference for nuclear matrix element calculations. We have conducted a search for two-neutrino double electron capture from the K-shell of Xe using 7636 kgd of data from the XENON100 dark matter detector. Using a Bayesian analysis we observed no significant excess above background, leading to a lower 90 % credibility limit on the half-life yr. We also evaluated the sensitivity of the XENON1T experiment, which is currently being commissioned, and find a sensitivity of yr after an exposure of 2 tyr
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