The XENON experiment is a 3500kg liquid xenon detector to search for the elusive Dark Matter. Have a look at the description of our detection principle, our recent publications, some pictures, or materials for press contacts. Feel free to contact us with your questions.
While the microscopic nature of dark matter in the Universe is largely unknown, the simplest assumption which can explain all existing observations is that it is made of a new, as yet undiscovered particle. Leading examples are weakly interacting massive particles (WIMPs), axions or axion-like particles (ALPs), and sterile neutrinos. WIMPs with masses in the GeV range, as well as axions/ALPs are examples for cold dark matter while sterile neutrinos with masses at the keV-scale are an example for warm dark matter. Cold dark matter particles were nonrelativistic at the time of their decoupling from the rest of the particles in the early universe. In contrast, warm dark matter particles remain relativistic for longer, retain a larger velocity dispersion, and thus more easily free-stream out from small-scale perturbations. Astrophysical and cosmological observations constrain the mass of warm dark matter to be larger than about 3keV/c2, with a more recent lower limit from Lyman-alpha forest data being 5.3keV/c2. Another example for warm dark matter particles are bosonic super-WIMPs. These particles, with masses at the keV-scale, could couple electromagnetically to standard model particles via the axioelectric effect, which is an analogous process to the photoelectric effect, and thus be detected in direct detection experiments.
We searched for vector and pseudo-scalar bosonic super-WIMPs with the XENON100 experiment. The super-WIMPs can be absorbed in liquid xenon and the expected signature is a monoenergetic peak at the super-WIMP’s rest mass. A profile likelihood analysis of data with an exposure of 224.6 live days × 34kg showed no evidence for a signal above the expected background. We thus obtained new upper limits in the (8 − 125) keV/c2 mass range, excluding couplings to electrons with coupling constants of gae > 3 × 10−13 for pseudo-scalar super-WIMPs and α′/α > 2 × 10−28 for vector super-WIMPs, respectively. We expect to improve upon these results with the XENON1T detector, which operates a larger mass of liquid xenon with reduced backgrounds. Our results were published in Physical Review D 96, 122002 (2017) and are of course also available at the arxiv.
XENON1T is currently the largest liquid xenon detector in the search for dark matter. To fully exploit the capabilities of the ton-scale target mass, a thorough understanding of radioactive background sources is required. In this paper we use the full data of the main science runs of the XENON100 experiment that were taken over a period of about 4 years to asses the target-intrinsic background sources radon (Rn-222), thoron (Rn-220) and krypton (Kr-85). We derive distributions of the individual radionuclides inside the detector (see Figure below) and quantify their abundances during the main three science runs. We find good agreement with external measurements of radon emanation and krypton concentrations, and report an observed reduction in concentrations of radon daughters that we attribute to the plating-out of charged ions on the negatively biased cathode.
The preprint of the full study is available on arXiv:1708.03617.
Figure: Spatial distributions of the various radon populations identified in XENON100.
Most direct detection searches focus on elastic scattering of galactic dark matter particles off nuclei, where the keV-scale nuclear recoil energy is to be detected. In this work, the alternative process of inelastic scattering is explored, where a WIMP-nucleus scattering induces a transition to a low-lying excited nuclear state. The experimental signature is a nuclear recoil detected together with the prompt de-excitation photon. We consider the scattering of dark matter particle off 129Xe isotope, which has an abundance of 26.4\% in natural xenon, and when excited to it lowest-lying 3/2+ state above the ground state it emits a 36.9 keV photon. This electromagnetic nuclear decay has a half-life of 0.97 ns.
The WIMP inelastic scattering is complementary to spin-dependent, elastic scattering, and dominates the integrated rates above 10 keV of deposited energy. In addition, in case of a positive signal, the observation of inelastic scattering would provide a clear indication of the spin-dependent nature of the fundamental interaction.
The search is performed using XENON100 Run-II science data, which corresponds to an exposure of 34×224.6 kg×days. No evidence of dark matter is found and a limit on dark matter inelastic interaction cross section is set. Our result, shown in the Figure, is the most stringent limit for the spin-dependent inelastic scattering to date, and set the stage for a sensitive search of inelastic WIMP-nucleus scattering in running or upcoming liquid xenon experiments such as XENON1T, XENONnT, LZ, and DARWIN.
The German GEOkompakt published an interview of our deputy spokesperson Laura Baudis, available here as PDF.
At the 62nd annual conference of the South African Institute of Physics (SAIP), hosted by the University of Stellenbosch, Jacques Pienaar presented the results of our first science run with XENON1T. While a dark matter particle candidate still eludes us, we are able to demonstrate that for the first time a tonne-scale liquid Xenon dark matter detector is not only operating, but doing so very successfully.
The work done up to this point has given us a thorough understanding of the electronic and nuclear recoil response in our detector, which we can use to look for dark matter candidates. This of course is just the start. In this first result we had an exposure of only 0.1 ton.years, but our design goal is 2 ton.years. Therefore much work still lies ahead to probe for dark matter, and indeed we have more than 3 times as much data available already to push the bounds of our knowledge further. Stay tuned!
On Tuesday 20th of June, we presented our latest results on Electronic Recoil Modulations with 4 years of Xenon100 data at the PASCOS 2017 conference held in Madrid. After a short introduction, by M.L. Benabderrahmane, to the dark matter modulation as a signal, the main results have been presented, namely the test statistics of unbinned profile likelihood to search for the modulation period using three different sets of data. The first set contains the single scatter events in the energy range 2-5.8keV, the second set contains Multiple scatter events in the same energy range and the last one contains single scatters in the energy range 6-20keV. The last two samples are used as a sideband. The results of the likelihood gives a period of 431 days which is different from the one observed by the DAMA/LIBRA collaboration. Our single scatter modulation at 431 days has a global significance below 2sigma. The local test statistics for one year period gives a 1.8sigma. Similarity of the spectra between the two control samples and the signal sample disfavors the possibility for a modulation due to Dark Matter interaction.
ReStoX is an original cryogenic system designed for experiments that make use of high quantities of liquid xenon. It allows to store the total amount of xenon in gaseous, liquid or solid phase and to fill it into the detector vessel under high purity conditions. The system is crucial in case of emergencies that might require a fast recovering of the whole xenon present in the detector. ReStoX is currently being used by the XENON1T experiment and a future upgrade for XENONnT has already started.
The traditional approach for WIMP nucleus interaction studies in direct detection experiment is to consider just two types of interactions, the spin independent (SI) and the spin dependent (SD) ones. However, these are not the only types of interactions possible. In recent years, a non-relativistic effective field theory approach has been studied. In this framework, 14 new interaction operators arise. These operators include the SI and SD ones among others. Some of these new operators are momentum dependent and predict a non-exponential event rate as function of energy, in contrast to the traditional expected signals. Moreover, some of these operators predict energy recoils above the upper threshold of the standard analyses done in direct detection experiments. For XENON100, this threshold is 43keV (nuclear recoil).
In this analysis, we extend the upper energy threshold up to ~240 keV. This value is dictated by low statistics in calibration data above it. We divide our signal region into two regimes, low recoil energy, on which we perform the same “standard” analysis done for the SI and SD cases, and high recoil energy, which is the main focus of this work.
We find that our data is compatible with background expectations. Using a binned profile likelihood, we thus produce 90% CL exclusion limits for both elastic scattering and inelastic WIMP scattering for each operator. Find the preprint of this study on the arxiv.