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.
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.
We report the results of a search for the inelastic scattering of weakly interacting massive particles (WIMPs) in the XENON1T dark matter experiment. Scattering off \(^{129}\)Xe is the most sensitive ...probe of inelastic WIMP interactions, with a signature of a 39.6 keV de-excitation photon detected simultaneously with the nuclear recoil. Using an exposure of 0.89 tonne-years, we find no evidence of inelastic WIMP scattering with a significance of more than 2\(\sigma\). A profile-likelihood ratio analysis is used to set upper limits on the cross-section of WIMP-nucleus interactions. We exclude new parameter space for WIMPs heavier than 100 GeV/c\({}^2\), with the strongest upper limit of \(3.3 \times 10^{-39}\) cm\({}^2\) for 130 GeV/c\({}^2\) WIMPs at 90\% confidence level.
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 \(^{222}\)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 \(^{222}\)Rn activity concentration of 10 \(\mu\)Bq/kg in 3.2 t of xenon. The knowledge of the distribution of the \(^{222}\)Rn sources allowed us to selectively eliminate critical components in the course of the experiment. The predictions from the emanation measurements were compared to data of the \(^{222}\)Rn activity concentration in XENON1T. The final \(^{222}\)Rn activity concentration of (4.5 \(\pm\) 0.1) \(\mu\)Bq/kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
XENONnT is a dark matter direct detection experiment, utilizing 5.9 t of instrumented liquid xenon, located at the INFN Laboratori Nazionali del Gran Sasso. In this work, we predict the experimental ...background and project the sensitivity of XENONnT to the detection of weakly interacting massive particles (WIMPs). The expected average differential background rate in the energy region of interest, corresponding to (1, 13) keV and (4, 50) keV for electronic and nuclear recoils, amounts to \(12.3 \pm 0.6\) (keV t y)\(^{-1}\) and \((2.2\pm 0.5)\times 10^{-3}\) (keV t y)\(^{-1}\), respectively, in a 4 t fiducial mass. We compute unified confidence intervals using the profile construction method, in order to ensure proper coverage. With the exposure goal of 20 t\(\,\)y, the expected sensitivity to spin-independent WIMP-nucleon interactions reaches a cross-section of \(1.4\times10^{-48}\) cm\(^2\) for a 50 GeV/c\(^2\) mass WIMP at 90% confidence level, more than one order of magnitude beyond the current best limit, set by XENON1T. In addition, we show that for a 50 GeV/c\(^2\) WIMP with cross-sections above \(2.6\times10^{-48}\) cm\(^2\) (\(5.0\times10^{-48}\) cm\(^2\)) the median XENONnT discovery significance exceeds 3\(\sigma\) (5\(\sigma\)). The expected sensitivity to the spin-dependent WIMP coupling to neutrons (protons) reaches \(2.2\times10^{-43}\) cm\(^2\) (\(6.0\times10^{-42}\) cm\(^2\)).
We report results from searches for new physics with low-energy electronic recoil data recorded with the XENON1T detector. With an exposure of 0.65 t-y and an unprecedentedly low background rate of ...\(76\pm2\) events/(t y keV) between 1 and 30 keV, the data enables sensitive searches for solar axions, an enhanced neutrino magnetic moment, and bosonic dark matter. An excess over known backgrounds is observed at low energies and most prominent between 2 and 3 keV. The solar axion model has a 3.4\(\sigma\) significance, and a 3D 90% confidence surface is reported for axion couplings to electrons, photons, and nucleons. This surface is inscribed in the cuboid defined by \(g_{ae}<3.8 \times 10^{-12}\), \(g_{ae}g_{an}^{eff}<4.8\times 10^{-18}\), and \(g_{ae}g_{a\gamma}<7.7\times10^{-22} GeV^{-1}\), and excludes either \(g_{ae}=0\) or \(g_{ae}g_{a\gamma}=g_{ae}g_{an}^{eff}=0\). The neutrino magnetic moment signal is similarly favored over background at 3.2\(\sigma\) and a confidence interval of \(\mu_{\nu} \in (1.4,2.9)\times10^{-11}\mu_B\) (90% C.L.) is reported. Both results are in strong tension with stellar constraints. The excess can also be explained by \(\beta\) decays of tritium at 3.2\(\sigma\) with a trace amount that can neither be confirmed nor excluded with current knowledge of its production and reduction mechanisms. The significances of the solar axion and neutrino magnetic moment hypotheses are reduced to 2.0\(\sigma\) and 0.9\(\sigma\), respectively, if an unconstrained tritium component is included in the fitting. With respect to bosonic dark matter, the excess favors a monoenergetic peak at (\(2.3\pm0.2\)) keV (68% C.L.) with a 3.0\(\sigma\) global (4.0\(\sigma\) local) significance. We also consider the possibility that \(^{37}\)Ar may be present in the detector and yield a 2.82 keV peak. Contrary to tritium, the \(^{37}\)Ar concentration can be tightly constrained and is found to be negligible.
Xenon dual-phase time projection chambers designed to search for Weakly Interacting Massive Particles have so far shown a relative energy resolution which degrades with energy above \(\sim\)200 keV ...due to the saturation effects. This has limited their sensitivity in the search for rare events like the neutrinoless double-beta decay of \(^{136}\)Xe at its \(Q\)-value, \(Q_{\beta\beta}\simeq\) 2.46 MeV. For the XENON1T dual-phase time projection chamber, we demonstrate that the relative energy resolution at 1 \(\sigma/\mu\) is as low as (0.80\(\pm\)0.02) % in its one-ton fiducial mass, and for single-site interactions at \(Q_{\beta\beta}\). We also present a new signal correction method to rectify the saturation effects of the signal readout system, resulting in more accurate position reconstruction and indirectly improving the energy resolution. The very good result achieved in XENON1T opens up new windows for the xenon dual-phase dark matter detectors to simultaneously search for other rare events.
Direct dark matter detection experiments based on a liquid xenon target are leading the search for dark matter particles with masses above \(\sim\) 5 GeV/c\(^2\), but have limited sensitivity to ...lighter masses because of the small momentum transfer in dark matter-nucleus elastic scattering. However, there is an irreducible contribution from inelastic processes accompanying the elastic scattering, which leads to the excitation and ionization of the recoiling atom (the Migdal effect) or the emission of a Bremsstrahlung photon. In this letter, we report on a probe of low-mass dark matter with masses down to about 85 MeV/c\(^2\) by looking for electronic recoils induced by the Migdal effect and Bremsstrahlung, using data from the XENON1T experiment. Besides the approach of detecting both scintillation and ionization signals, we exploit an approach that uses ionization signals only, which allows for a lower detection threshold. This analysis significantly enhances the sensitivity of XENON1T to light dark matter previously beyond its reach.
