The DARWIN observatory is a proposed next-generation experiment to search for particle dark matter and for the neutrinoless double beta decay of \(^{136}\)Xe. Out of its 50\(\,\)t total natural xenon ...inventory, 40\(\,\)t will be the active target of a time projection chamber which thus contains about 3.6 t of \(^{136}\)Xe. Here, we show that its projected half-life sensitivity is \(2.4\times10^{27}\,\)yr, using a fiducial volume of 5t of natural xenon and 10\(\,\)yr of operation with a background rate of less than 0.2\(~\)events/(t\(\cdot\)yr) in the energy region of interest. This sensitivity is based on a detailed Monte Carlo simulation study of the background and event topologies in the large, homogeneous target. DARWIN will be comparable in its science reach to dedicated double beta decay experiments using xenon enriched in \(^{136}\)Xe.
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.
We report constraints on light dark matter (DM) models using ionization signals in the XENON1T experiment. We mitigate backgrounds with strong event selections, rather than requiring a scintillation ...signal, leaving an effective exposure of \((22 \pm 3)\) tonne-days. Above \(\sim\!0.4\,\mathrm{keV}_\mathrm{ee}\), we observe \(<1 \, \text{event}/(\text{tonne} \times \text{day} \times \text{keV}_\text{ee})\), which is more than one thousand times lower than in similar searches with other detectors. Despite observing a higher rate at lower energies, no DM or CEvNS detection may be claimed because we cannot model all of our backgrounds. We thus exclude new regions in the parameter spaces for DM-nucleus scattering for DM masses \(m_\chi\) within \(3-6\,\mathrm{GeV}/\mathrm{c}^2\), DM-electron scattering for \(m_\chi > 30\,\mathrm{MeV}/\mathrm{c}^2\), and absorption of dark photons and axion-like particles for \(m_\chi\) within \(0.186 - 1 \, \mathrm{keV}/\mathrm{c}^2\).
The XENON1T experiment at the Laboratori Nazionali del Gran Sasso is the most sensitive direct detection experiment for dark matter in the form of weakly interacting particles (WIMPs) with masses ...above \(6\,\)GeV/\(c^2\) scattering off nuclei. The detector employs a dual-phase time projection chamber with 2.0 metric tons of liquid xenon in the target. A one metric \(\mathrm{ton}\times\mathrm{year}\) exposure of science data was collected between October 2016 and February 2018. This article reports on the performance of the detector during this period and describes details of the data analysis that led to the most stringent exclusion limits on various WIMP-nucleon interaction models to date. In particular, signal reconstruction, event selection and calibration of the detector response to nuclear and electronic recoils in XENON1T are discussed.
The XENON1T liquid xenon time projection chamber is the most sensitive detector built to date for the measurement of direct interactions of weakly interacting massive particles with normal matter. ...The data acquisition system (DAQ) is constructed from commercial, open source, and custom components to digitize signals from the detector and store them for later analysis. The system achieves an extremely low signal threshold below a tenth of a photoelectron using a parallelized readout with the global trigger deferred to a later, software stage. The event identification is based on MongoDB database queries and has over 97% efficiency at recognizing interactions at the analysis energy threshold. A readout bandwidth over 300 MB/s is reached in calibration modes and is further expandable via parallelization. This DAQ system was successfully used during three years of operation of XENON1T.
We report the first experimental results on spin-dependent elastic weakly interacting massive particle (WIMP) nucleon scattering from the XENON1T dark matter search experiment. The analysis uses the ...full ton year exposure of XENON1T to constrain the spin-dependent proton-only and neutron-only cases. No significant signal excess is observed, and a profile likelihood ratio analysis is used to set exclusion limits on the WIMP-nucleon interactions. This includes the most stringent constraint to date on the WIMP-neutron cross section, with a minimum of \(6.3\times10^{-42}\) cm\(^2\) at 30 GeV/c\({}^2\) and 90% confidence level. The results are compared with those from collider searches and used to exclude new parameter space in an isoscalar theory with an axial-vector mediator.
Two-neutrino double electron capture (\(2\nu\)ECEC) is a second-order Weak process with predicted half-lives that surpass the age of the Universe by many orders of magnitude. Until now, indications ...for \(2\nu\)ECEC decays have only been seen for two isotopes, \(^{78}\)Kr and \(^{130}\)Ba, and instruments with very low background levels are needed to detect them directly with high statistical significance. The \(2\nu\)ECEC half-life provides an important input for nuclear structure models and its measurement represents a first step in the search for the neutrinoless double electron capture processes (\(0\nu\)ECEC). A detection of the latter would have implications for the nature of the neutrino and give access to the absolute neutrino mass. Here we report on the first direct observation of \(2\nu\)ECEC in \(^{124}\)Xe with the XENON1T Dark Matter detector. The significance of the signal is \(4.4\sigma\) and the corresponding half-life \(T_{1/2}^{2\nu\text{ECEC}} = (1.8\pm 0.5_\text{stat}\pm 0.1_\text{sys})\times 10^{22}\;\text{y}\) is the longest ever measured directly. This study demonstrates that the low background and large target mass of xenon-based Dark Matter detectors make them well suited to measuring other rare processes as well, and it highlights the broad physics reach for even larger next-generation experiments.
The XENON1T experiment searches for dark matter particles through their scattering off xenon atoms in a 2 tonne liquid xenon target. The detector is a dual-phase time projection chamber, which ...measures simultaneously the scintillation and ionization signals produced by interactions in target volume, to reconstruct energy and position, as well as the type of the interaction. The background rate in the central volume of XENON1T detector is the lowest achieved so far with a liquid xenon-based direct detection experiment. In this work we describe the response model of the detector, the background and signal models, and the statistical inference procedures used in the dark matter searches with a 1 tonne\(\times\)year exposure of XENON1T data, that leaded to the best limit to date on WIMP-nucleon spin-independent elastic scatter cross-section for WIMP masses above 6 GeV/c\(^2\).
We present first results on the scalar WIMP-pion coupling from 1 t\(\times\)yr of exposure with the XENON1T experiment. This interaction is generated when the WIMP couples to a virtual pion exchanged ...between the nucleons in a nucleus. In contrast to most non-relativistic operators, these pion-exchange currents can be coherently enhanced by the total number of nucleons, and therefore may dominate in scenarios where spin-independent WIMP-nucleon interactions are suppressed. Moreover, for natural values of the couplings, they dominate over the spin-dependent channel due to their coherence in the nucleus. Using the signal model of this new WIMP-pion channel, no significant excess is found, leading to an upper limit cross section of \(6.4\times10^{-46}\) cm\(^2\) (90 % confidence level) at 30 GeV/c\(^2\) WIMP mass.
