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We present results of a search for spin-independent dark matter-nucleus interactions in a $1{\mathrm{cm}}^2$by 1 mm thick (0.233 g) high-resolution silicon athermal phonon detector operated above ground. For interactions in the substrate, this detector achieves an rms baseline energy resolution of $361.5\left(4\right)\mathrm{m}\mathrm{eV}$(statistical error), the best for any athermal phonon detector to date. With an exposure of $0.233\mathrm{g}\times 12$hours, we place the most stringent constraints on dark matter masses between 44 and $87\mathrm{M}\mathrm{eV}/{\mathrm{c}}^2$, with the lowest unexplored cross section of $4\times {10}^{-32}{\mathrm{c}\mathrm{m}}^2$at $87\mathrm{M}\mathrm{eV}/{\mathrm{c}}^2$. We employ a conservative salting technique to reach the lowest dark matter mass ever probed via direct detection experiment. This constraint is enabled by two-channel rejection of low energy backgrounds that are coupled to individual sensors. 

This paper details the first application of a software tagging algorithm to reduce radon-induced backgrounds in liquid noble element time projection chambers, such as XENON1T and XENONnT. The convection velocity field in XENON1T was mapped out using ${}^{222}\mathrm{Rn}$and ${}^{218}\mathrm{Po}$events, and the rms convection speed was measured to be $0.30\pm 0.01\mathrm{cm}/\mathrm{s}$. Given this velocity field, ${}^{214}\mathrm{Pb}$background events can be tagged when they are followed by ${}^{214}\mathrm{Bi}$and ${}^{214}\mathrm{Po}$decays, or preceded by ${}^{218}\mathrm{Po}$decays. This was achieved by evolving a point cloud in the direction of a measured convection velocity field, and searching for ${}^{214}\mathrm{Bi}$and ${}^{214}\mathrm{Po}$decays or ${}^{218}\mathrm{Po}$decays within a volume defined by the point cloud. In XENON1T, this tagging system achieved a ${}^{214}\mathrm{Pb}$background reduction of ${6.2}_{-0.9}^{+0.4}\%$with an exposure loss of $1.8\pm 0.2\%$, despite the timescales of convection being smaller than the relevant decay times. We show that the performance can be improved in XENONnT, and that the performance of such a software-tagging approach can be expected to be further improved in a diffusion-limited scenario. Finally, a similar method might be useful to tag the cosmogenic ${}^{137}\mathrm{Xe}$background, which is relevant to the search for neutrinoless double-beta decay. Published by the American Physical Society2024 

Abstract The precision in reconstructing events detected in a dual-phase time projection chamber depends on an homogeneous and well understood electric field within the liquid target. In the XENONnT TPC the field homogeneity is achieved through a double-array field cage, consisting of two nested arrays of field shaping rings connected by an easily accessible resistor chain. Rather than being connected to the gate electrode, the topmost field shaping ring is independently biased, adding a degree of freedom to tune the electric field during operation. Two-dimensional finite element simulations were used to optimize the field cage, as well as its operation. Simulation results were compared to$${}^{83\textrm{m}}\hbox {Kr }$$ ${}^{83\text{m}}\text{Kr}$calibration data. This comparison indicates an accumulation of charge on the panels of the TPC which is constant over time, as no evolution of the reconstructed position distribution of events is observed. The simulated electric field was then used to correct the charge signal for the field dependence of the charge yield. This correction resolves the inconsistent measurement of the drift electron lifetime when using different calibrations sources and different field cage tuning voltages. 

Abstract A low-energy electronic recoil calibration of XENON1T, a dual-phase xenon time projection chamber, with an internal $${}^{37}$$ 37 Ar source was performed. This calibration source features a 35-day half-life and provides two mono-energetic lines at 2.82 keV and 0.27 keV. The photon yield and electron yield at 2.82 keV are measured to be ( $$32.3\,\pm \,0.3$$ 32.3 ± 0.3 ) photons/keV and ( $$40.6\,\pm \,0.5$$ 40.6 ± 0.5 ) electrons/keV, respectively, in agreement with other measurements and with NEST predictions. The electron yield at 0.27 keV is also measured and it is ( $$68.0^{+6.3}_{-3.7}$$ 68 . 0 - 3.7 + 6.3 ) electrons/keV. The $${}^{37}$$ 37 Ar calibration confirms that the detector is well-understood in the energy region close to the detection threshold, with the 2.82 keV line reconstructed at ( $$2.83\,\pm \,0.02$$ 2.83 ± 0.02 ) keV, which further validates the model used to interpret the low-energy electronic recoil excess previously reported by XENON1T. The ability to efficiently remove argon with cryogenic distillation after the calibration proves that $${}^{37}$$ 37 Ar can be considered as a regular calibration source for multi-tonne xenon detectors. 

Abstract The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector.