This content will become publicly available on November 1, 2023

An approximate likelihood for nuclear recoil searches with XENON1T data
Abstract 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 t-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 t-year exposure.
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Award ID(s):
Publication Date:
NSF-PAR ID:
10380340
Journal Name:
The European Physical Journal C
Volume:
82
Issue:
11
ISSN:
1434-6052
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\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\mu \mathrm{Bq}/\mathrm{kg}$in$$3.2\,\mathrm{t}$$$3.2\phantom{\rule{0ex}{0ex}}t$of xenon. The knowledge of the distribution of the$$^{222}$$${}^{222}$Rn sources allowed us to selectively 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$$(4.5\pm 0.1)\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$$\left(4.5±0.1\right)\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\mu \mathrm{Bq}/\mathrm{kg}$in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
5. 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 low 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.