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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$$^{222}$$${}^{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$$^{222}$$${}^{222}$Rn activity concentration of$$10\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$$10\mu \mathrm{Bq}/\mathrm{kg}$in$$3.2\,\mathrm{t}$$$3.2t$of xenon. The knowledge of the distribution of the$$^{222}$$${}^{222}$Rn sources allowed us to selectivelymore »eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the$$^{222}$$${}^{222}$Rn activity concentration in XENON1T. The final$$^{222}$$${}^{222}$Rn activity concentration of$$(4.5\pm 0.1)\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$$(4.5\pm 0.1)\mu \mathrm{Bq}/\mathrm{kg}$in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.

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Abstract 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 $$^{136} \hbox {Xe}$$ 136 Xe at its Q value, $$Q_{\beta \beta }\simeq 2.46\,\hbox {MeV}$$ Q β β ≃ 2.46 MeV . For the XENON1T dual-phase time projection chamber, we demonstrate that the relative energy resolution at $$1\,\sigma /\mu $$ 1 σ / μ is as lowmore »as ( $$0.80 \pm 0.02$$ 0.80 ± 0.02 ) % in its one-ton fiducial mass, and for single-site interactions at $$Q_{\beta \beta }$$ Q β β . 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.« less

Aria is a plant hosting a$${350}\,\hbox {m}$$$350\text{m}$cryogenic isotopic distillation column, the tallest ever built, which is being installed in a mine shaft at Carbosulcis S.p.A., Nuraxi-Figus (SU), Italy. Aria is one of the pillars of the argon dark-matter search experimental program, lead by the Global Argon Dark Matter Collaboration. It was designed to reduce the isotopic abundance of$${^{39}\hbox {Ar}}$$${}^{39}\text{Ar}$in argon extracted from underground sources, called Underground Argon (UAr), which is used for dark-matter searches. Indeed,$${^{39}\hbox {Ar}}$$${}^{39}\text{Ar}$is a$$\beta $$$\beta$-emitter of cosmogenic origin, whose activity poses background and pile-up concerns in the detectors. In this paper, we discuss the requirements, design,more »construction, tests, and projected performance of the plant for the isotopic cryogenic distillation of argon. We also present the successful results of the isotopic cryogenic distillation of nitrogen with a prototype plant.

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Abstract Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The “standard” EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neutral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is duemore »to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.« less