We perform a low-mass dark matter search using an exposure of 30 kg×yr with the XENON100 detector. By dropping the requirement of a scintillation signal and using only the ionization signal to ...determine the interaction energy, we lowered the energy threshold for detection to 0.7 keV for nuclear recoils. No dark matter detection can be claimed because a complete background model cannot be constructed without a primary scintillation signal. Instead, we compute an upper limit on the WIMP-nucleon scattering cross section under the assumption that every event passing our selection criteria could be a signal event. Using an energy interval from 0.7 keV to 9.1 keV, we derive a limit on the spin-independent WIMP-nucleon cross section that excludes WIMPs with a mass of 6 GeV/c2 above 1.4×10−41 cm2 at 90% confidence level.
We report on weakly interacting massive particles (WIMPs) search results in the XENON100 detector using a nonrelativistic effective field theory approach. The data from science run II (34 kg×224.6 ...live days) were reanalyzed, with an increased recoil energy interval compared to previous analyses, ranging from (6.6–240) keVnr. The data are found to be compatible with the background-only hypothesis. We present 90% confidence level exclusion limits on the coupling constants of WIMP-nucleon effective operators using a binned profile likelihood method. We also consider the case of inelastic WIMP scattering, where incident WIMPs may up-scatter to a higher mass state, and set exclusion limits on this model as well.
A Rn220 source is deployed on the XENON100 dark matter detector in order to address the challenges in calibration of tonne-scale liquid noble element detectors. We show that the Pb212 beta emission ...can be used for low-energy electronic recoil calibration in searches for dark matter. The isotope spreads throughout the entire active region of the detector, and its activity naturally decays below background level within a week after the source is closed. We find no increase in the activity of the troublesome Rn222 background after calibration. Alpha emitters are also distributed throughout the detector and facilitate calibration of its response to Rn222. Using the delayed coincidence of Rn220−Po216, we map for the first time the convective motion of particles in the XENON100 detector. Additionally, we make a competitive measurement of the half-life of Po212, t1/2=(293.9±(1.0)stat±(0.6)sys) ns.
We report on a search for electronic recoil event rate modulation signatures in the XENON100 data accumulated over a period of 4 yr, from January 2010 to January 2014. A profile likelihood method, ...which incorporates the stability of the XENON100 detector and the known electronic recoil background model, is used to quantify the significance of periodicity in the time distribution of events. There is a weak modulation signature at a period of 431_{-14}^{+16} day in the low energy region of (2.0-5.8) keV in the single scatter event sample, with a global significance of 1.9σ; however, no other more significant modulation is observed. The significance of an annual modulation signature drops from 2.8σ, from a previous analysis of a subset of this data, to 1.8σ with all data combined. Single scatter events in the low energy region are thus used to exclude the DAMA/LIBRA annual modulation as being due to dark matter electron interactions via axial vector coupling at 5.7σ.
Abstract
The selection of low-radioactive construction materials is of utmost importance for the success of low-energy rare event search experiments. Besides radioactive contaminants in the bulk, the ...emanation of radioactive radon atoms from material surfaces attains increasing relevance in the effort to further reduce the background of such experiments. In this work, we present the
$$^{222}$$
222
Rn emanation measurements performed for the XENON1T dark matter experiment. Together with the bulk impurity screening campaign, the results enabled us to select the radio-purest construction materials, targeting a
$$^{222}$$
222
Rn activity concentration of
$$10\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$
10
μ
Bq
/
kg
in
$$3.2\,\mathrm{t}$$
3.2
t
of xenon. The knowledge of the distribution of the
$$^{222}$$
222
Rn sources allowed us to selectively eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the
$$^{222}$$
222
Rn activity concentration in XENON1T. The final
$$^{222}$$
222
Rn activity concentration of
$$(4.5\pm 0.1)\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$
(
4.5
±
0.1
)
μ
Bq
/
kg
in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
In this paper, we describe the XENON100 data analyses used to assess the target-intrinsic background sources radon (
), thoron (
) and krypton (
). We detail the event selections of high-energy alpha ...particles and decay-specific delayed coincidences. We derive distributions of the individual radionuclides inside the detector and quantify their abundances during the main three science runs of the experiment over a period of
∼
4
years
, from January 2010 to January 2014. We compare our results to external measurements of radon emanation and krypton concentrations where we find good agreement. We report an observed reduction in concentrations of radon daughters that we attribute to the plating-out of charged ions on the negatively biased cathode.
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