Abstract 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 μ Bq / kg in $$3.2\,\mathrm{t}$$ 3.2 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 $$(4.5\pm 0.1)\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$ ( 4.5 ± 0.1 ) μ Bq / kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
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
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
Rn activity concentration of
10
μ
Bq
/
kg
in
3.2
t
of xenon. The knowledge of the distribution of the
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
Rn activity concentration in XENON1T. The final
222
Rn activity concentration of
(
4.5
±
0.1
)
μ
Bq
/
kg
in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
Photomultiplier tubes (PMTs) are often used in low-background particle physics experiments, which rely on an excellent response to single-photon signals and stable long-term operation. In particular, ...the Hamamatsu R11410 model is the light sensor of choice for liquid xenon dark matter experiments, including XENONnT. The same PMT model was also used for the predecessor, XENON1T, where issues affecting its long-term operation were observed. Here, we report on an improved PMT testing procedure which ensures optimal performance in XENONnT. Using both new and upgraded facilities, we tested 368 new PMTs in a cryogenic xenon environment. We developed new tests targeted at the detection of light emission and the degradation of the PMT vacuum through small leaks, which can lead to spurious signals known as afterpulses, both of which were observed in XENON1T. We exclude the use of 26 of the 368 tested PMTs and categorise the remainder according to their performance. Given that we have improved the testing procedure, yet we rejected fewer PMTs, we expect significantly better PMT performance in XENONnT.
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 \(^{222}\)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 \(^{222}\)Rn activity concentration of 10 \(\mu\)Bq/kg in 3.2 t of xenon. The knowledge of the distribution of the \(^{222}\)Rn sources allowed us to selectively eliminate critical components in the course of the experiment. The predictions from the emanation measurements were compared to data of the \(^{222}\)Rn activity concentration in XENON1T. The final \(^{222}\)Rn activity concentration of (4.5 \(\pm\) 0.1) \(\mu\)Bq/kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
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 \(0.186 - 1 \, \mathrm{keV}/\mathrm{c}^2\).
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