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In this work, we expand on the XENON1T nuclear recoil searches to study the individual signals of dark matter interactions from operators up to dimension-eight in a Chiral Effective Field Theory (ChEFT) and a model of inelastic dark matter (iDM). We analyze data from two science runs of the XENON1T detector totaling 1\\,tonne\\(\\times\\)year exposure. For these analyses, we extended the region of interest from [4.9, 40.9]\\(\\,\\)keV\\(_{\\text{NR}}\\) to [4.9, 54.4]\\(\\,\\)keV\\(_{\\text{NR}}\\) to enhance our sensitivity for signals that peak at nonzero energies. We show that the data is consistent with the background-only hypothesis, with a small background over-fluctuation observed peaking between 20 and 50\\(\\,\\)keV\\(_{\\text{NR}}\\), resulting in a maximum local discovery significance of 1.7\\,\\(\\sigma\\) for the Vector\\(\\otimes\\)Vector\\(_{\\text{strange}}\\) (\\(VV_s\\)) ChEFT channel for a dark matter particle of 70\\(\\,\\)GeV/c\\(^2\\), and \\(1.8\\,\\sigma\\) for an iDM particle of 50\\(\\,\\)GeV/c\\(^2\\) with a mass splitting of 100\\(\\,\\)keV/c\\(^2\\). For each model, we report 90\\,\\% confidence level (CL) upper limits. We also report upper limits on three benchmark models of dark matter interaction using ChEFT where we investigate the effect of isospin-breaking interactions. We observe rate-driven cancellations in regions of the isospin-breaking couplings, leading to up to 6 orders of magnitude weaker upper limits with respect to the isospin-conserving case.

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.

The selection of low-radioactive construction materials is of the utmost importance for rare-event searches and thus critical to the XENONnT experiment. Results of an extensive radioassay program are reported, in which material samples have been screened with gamma-ray spectroscopy, mass spectrometry, and \\(^{222}\\)Rn emanation measurements. Furthermore, the cleanliness procedures applied to remove or mitigate surface contamination of detector materials are described. Screening results, used as inputs for a XENONnT Monte Carlo simulation, predict a reduction of materials background (\\(\\sim\\)17%) with respect to its predecessor XENON1T. Through radon emanation measurements, the expected \\(^{222}\\)Rn activity concentration in XENONnT is determined to be 4.2\\(\\,(^{+0.5}_{-0.7})\\,\\mu\\)Bq/kg, a factor three lower with respect to XENON1T. This radon concentration will be further suppressed by means of the novel radon distillation system.

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.

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 a 3.3 \\(\\) measurement of coherent elastic neutrino-nucleus scattering from solar \\(^8\\)B neutrinos using a 6.77 t\\(\\)yr exposure from the XENONnT experiment, inferring a solar \\(^8\\)B neutrino flux of \\((5_-2^+3) 10^6\\,cm^-2s^-1\\), consistent with previous measurements. In the presence of the \\(^8\\)B \"neutrino fog\", we find no evidence for light dark matter, and observe diminishing returns in sensitivity with increasing exposure. A 93% increase in exposure from the previous search improves the median sensitivity to 5 GeV/\\(c^2\\) weakly interacting massive particles-nucleon cross section by 10%. The dataset was also used to measure the weak mixing angle at \\(\\) 0.02 GeV/\\(c\\) momentum transfer and constrain physics beyond the Standard Model.

Dual-phase time projection chamber (TPC) that employs a multi-ton-scale liquid xenon (LXe) target mass is a pioneering detector technology to search for dark matter. Beyond its advantage in dark matter direct detection efforts, the natural xenon target allows it to search for the neutrinoless double-beta decay (\\(0\\nu\\beta\\beta\\)) process, which would violate lepton number conservation and indicate that neutrinos are Majorana particles. However, such \\(0\\nu\\beta\\beta\\) searches have been limited by gamma-ray backgrounds originating from the detector materials. In this work, we designed an augmented convolutional neural network (A-CNN) model to extract additional event-topology information from detector data. Using simulation and calibration data from XENONnT, a leading LXe TPC experiment, our model achieved over 60% background rejection while maintaining 90% signal acceptance. This rejection power improves XENONnT's projected sensitivity of the \\(^{136}\\)Xe \\(0\\nu\\beta\\beta\\) search by about 40%. The implementation of A-CNN in the data analysis of future liquid xenon observatories, such as XLZD, will further enhance their sensitivities for \\(0\\nu\\beta\\beta\\) with \\(^{136}\\)Xe.

We report on a blinded search for dark matter (DM) using ionization-only (S2-only) signals in XENONnT with a total exposure of \\(7.83\\mathrm{tonne}\\times\\mathrm{year}\\) over 579 days in three science runs. Dedicated background suppression techniques and the first complete S2-only background model in XENONnT provide sensitivity to nuclear recoils of [0.5, 5.0] \\(\\mathrm{keV_\\mathrm{nr}}\\) and electronic recoils of [0.04, 0.7] \\(\\mathrm{keV_\\mathrm{ee}}\\). No significant excess over the expected background is observed, and we set 90\\% confidence level upper limits on spin-independent DM--nucleon and spin-dependent DM--neutron scattering for DM masses between 3 and 8 \\(\\mathrm{GeV}/c^2\\), as well as on DM--electron scattering, axion-like particles, and dark photons, improving on previous constraints. For spin-independent DM--nucleon scattering, we exclude cross sections above \\(6.0\\times10^{-45} \\)cm\\(^2\\) at a DM mass of 5 \\(\\mathrm{GeV}/c^2\\), pushing the XENONnT sensitivity closer to the region where coherent elastic neutrino-nucleus scattering (\\(\\text{CE}\\nu\\text{NS}\\)) becomes an irreducible background.

We report on a search for sub-GeV dark matter upscattered via the solar reflection mechanism in the heavy mediator scenario. Under the Standard Halo Model, keV to MeV dark matter produces nuclear recoils with energies below the detection threshold of liquid xenon time projection chambers. We enhance sensitivity to low-mass dark matter by considering dark matter-electron scattering, employing dedicated event selections to reduce the detection threshold, and exploiting the additional kinetic energy imparted to the dark matter particle by solar upscattering. Using XENON1T ionization-only and XENONnT low-energy electronic recoil datasets, we exclude previously unconstrained DM-electron scattering cross section for masses between \\(4.6\\, \\text{keV/}c^2\\) and \\(20\\, \\text{keV/}c^2\\), and between \\(0.2\\, \\text{MeV/}c^2\\) and \\(2\\, \\text{MeV/}c^2\\), reaching a minimum of \\(3.41\\times10^{-39}\\, \\text{cm}^2\\) for a mass of \\(0.3\\, \\text{MeV/}c^2\\) at 90\\% confidence level.

We report the measurement of the \\(^214\\)Bi beta-decay spectrum to the ground state of \\(^214\\)Po using the XENONnT detector. This decay is classified as first-forbidden non-unique, for which theoretical predictions require detailed nuclear structure modeling. A dedicated identification algorithm isolates a high-purity sample of ground-state beta-decays, explicitly excluding events with associated gamma-rays emission. By comparing the measured spectrum, which covers energies up to 3.27 MeV, with several nuclear models, we find that the prediction based on the conserved vector current (CVC) hypothesis provides the best description of the data. Using this dataset, we additionally derive charge and light yield curves for electronic recoils, extending detector response modeling up to the MeV scale.