The XENON collaboration has published stringent limits on specific dark matter -nucleon recoil spectra from dark matter recoiling on the liquid xenon detector target. In this paper, we present an ...approximate likelihood for the XENON1T 1 tonne-year nuclear recoil search applicable to any nuclear recoil spectrum. Alongside this paper, we publish data and code to compute upper limits using the method we present. The approximate likelihood is constructed in bins of reconstructed energy, profiled along the signal expectation in each bin. This approach can be used to compute an approximate likelihood and therefore most statistical results for any nuclear recoil spectrum. Computing approximate results with this method is approximately three orders of magnitude faster than the likelihood used in the original publications of XENON1T, where limits were set for specific families of recoil spectra. Using this same method, we include toy Monte Carlo simulation-derived binwise likelihoods for the upcoming XENONnT experiment that can similarly be used to assess the sensitivity to arbitrary nuclear recoil signatures in its eventual 20 tonne-year exposure.
We present results on the search for double-electron capture (\(2\nu\text{ECEC}\)) of \(^{124}\)Xe and neutrinoless double-\(\beta\) decay (\(0\nu\beta\beta\)) of \(^{136}\)Xe in XENON1T. We consider ...captures from the K- up to the N-shell in the \(2\nu\text{ECEC}\) signal model and measure a total half-life of \(T_{1/2}^{2\nu\text{ECEC}}=(1.1\pm0.2_\text{stat}\pm0.1_\text{sys})\times 10^{22}\;\text{yr}\) with a \(0.87\;\text{kg}\times\text{yr}\) isotope exposure. The statistical significance of the signal is \(7.0\,\sigma\). We use XENON1T data with \(36.16\;\text{kg}\times\text{yr}\) of \(^{136}\)Xe exposure to search for \(0\nu\beta\beta\). We find no evidence of a signal and set a lower limit on the half-life of \(T_{1/2}^{0\nu\beta\beta} > 1.2 \times 10^{24}\;\text{yr}\; \text{at}\; 90\,\%\;\text{CL}\). This is the best result from a dark matter detector without an enriched target to date. We also report projections on the sensitivity of XENONnT to \(0\nu\beta\beta\). Assuming a \(275\;\text{kg}\times\text{yr}\) \(^{136}\)Xe exposure, the expected sensitivity is \(T_{1/2}^{0\nu\beta\beta} > 2.1 \times 10^{25}\;\text{yr}\; \text{at}\; 90\,\%\;\text{CL}\), corresponding to an effective Majorana mass range of \(\langle m_{\beta\beta} \rangle < (0.19 - 0.59)\;\text{eV/c}^2\).
Delayed single- and few-electron emissions plague dual-phase time projection chambers, limiting their potential to search for light-mass dark matter. This paper examines the origins of these events ...in the XENON1T experiment. Characterization of the intensity of delayed electron backgrounds shows that the resulting emissions are correlated, in time and position, with high-energy events and can effectively be vetoed. In this work we extend previous S2-only analyses down to a single electron. From this analysis, after removing the correlated backgrounds, we observe rates < 30 events/(electron*kg*day) in the region of interest spanning 1 to 5 electrons. We derive 90% confidence upper limits for dark matter-electron scattering, first direct limits on the electric dipole, magnetic dipole, and anapole interactions, and bosonic dark matter models, where we exclude new parameter space for dark photons and solar dark photons.
Understanding propagation of scintillation light is critical for maximizing the discovery potential of next-generation liquid xenon detectors that use dual-phase time projection chamber technology. ...This work describes a detailed optical simulation of the DARWIN detector implemented using Chroma, a GPU-based photon tracking framework. To evaluate the framework and to explore ways of maximizing efficiency and minimizing the time of light collection, we simulate several variations of the conventional detector design. Results of these selected studies are presented. More generally, we conclude that the approach used in this work allows one to investigate alternative designs faster and in more detail than using conventional Geant4 optical simulations, making it an attractive tool to guide the development of the ultimate liquid xenon observatory.
A novel online distillation technique was developed for the XENON1T dark matter experiment to reduce intrinsic background components more volatile than xenon, such as krypton or argon, while the ...detector was operating. The method is based on a continuous purification of the gaseous volume of the detector system using the XENON1T cryogenic distillation column. A krypton-in-xenon concentration of \((360 \pm 60)\) ppq was achieved. It is the lowest concentration measured in the fiducial volume of an operating dark matter detector to date. A model was developed and fit to the data to describe the krypton evolution in the liquid and gas volumes of the detector system for several operation modes over the time span of 550 days, including the commissioning and science runs of XENON1T. The online distillation was also successfully applied to remove Ar-37 after its injection for a low energy calibration in XENON1T. This makes the usage of Ar-37 as a regular calibration source possible in the future. The online distillation can be applied to next-generation experiments to remove krypton prior to, or during, any science run. The model developed here allows further optimization of the distillation strategy for future large scale detectors.
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