Dual-phase Xenon Time Projection Chamber Research Articles

The design, implementation, and performance of the LZ calibration systems

LUX-ZEPLIN (LZ) is a tonne-scale experiment searching for direct dark matter interactions and other rare events. It is located at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. The core of the LZ detector is a dual-phase xenon time projection chamber (TPC), designed with the primary goal of detecting Weakly Interacting Massive Particles (WIMPs) via their induced low energy nuclear recoils. Surrounding the TPC, two veto detectors immersed in an ultra-pure water tank enable reducing background events to enhance the discovery potential. Intricate calibration systems are purposely designed to precisely understand the responses of these three detector volumes to various types of particle interactions and to demonstrate LZ's ability to discriminate between signals and backgrounds. In this paper, we present a comprehensive discussion of the key features, requirements, and performance of the LZ calibration systems, which play a crucial role in enabling LZ's WIMP-search and its broad science program. The thorough description of these calibration systems, with an emphasis on their novel aspects, is valuable for future calibration efforts in direct dark matter and other rare-event search experiments.

First constraints on WIMP-nucleon effective field theory couplings in an extended energy region from LUX-ZEPLIN

Following the first science results of the LUX-ZEPLIN (LZ) experiment, a dual-phase xenon time projection chamber operating from the Sanford Underground Research Facility in Lead, South Dakota, USA, we report the initial limits on a model-independent nonrelativistic effective field theory describing the complete set of possible interactions of a weakly interacting massive particle (WIMP) with a nucleon. These results utilize the same 5.5 t fiducial mass and 60 live days of exposure collected for the LZ spin-independent and spin-dependent analyses while extending the upper limit of the energy region of interest by a factor of 7.5 to 270 keV. No significant excess in this high energy region is observed. Using a profile-likelihood ratio analysis, we report 90% confidence level exclusion limits on the coupling of each individual nonrelativistic WIMP-nucleon operator for both elastic and inelastic interactions in the isoscalar and isovector bases. Published by the American Physical Society 2024

Dual-phase xenon time projection chambers forrare-event searches.

In the past decade, dual-phase xenon time projection chambers (Xe-TPCs) have emerged as some of the most powerful detectors in the fields of astroparticle physics and rare-event searches. Developed primarily towards the direct detection of dark matter particles, experiments presently operating deep underground have reached target masses at the multi-tonne scale, energy thresholds of approximately 1 keV and radioactivity-induced background rates similar to those from solar neutrinos. These unique properties, together with demonstrated stable operation over several years, allow for the exploration of new territory via high-sensitivity searches for a plethora of ultra-rare interactions. These include searches for particle dark matter, for second-order weak decays, and the observation of astrophysical neutrinos. We first review some properties of xenon as a radiation detection medium and the operation principles of dual-phase Xe-TPCs together with their energy calibration and resolution. We then discuss the status of currently running experiments and of proposed next-generation projects, describing some of the technological challenges. We end by looking at their sensitivity to dark matter candidates, to second-order weak decays and to solar and supernova neutrinos. Experiments based on dual-phase Xe-TPCs are difficult and, like all good experiments, they are constantly pushed to their limits. Together with many other endeavours in astroparticle physics and cosmology they will continue to push at the borders of the unknown, hopefully to reveal profound new knowledge about our cosmos. This article is part of the theme issue 'The particle-gravity frontier'.

First Dark Matter Search Results from the LUX-ZEPLIN (LZ) Experiment.

The LUX-ZEPLIN experiment is a dark matter detector centered on a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility in Lead, South Dakota, USA. This Letter reports results from LUX-ZEPLIN's first search for weakly interacting massive particles (WIMPs) with an exposure of 60 live days using a fiducial mass of 5.5t. A profile-likelihood ratio analysis shows the data to be consistent with a background-only hypothesis, setting new limits on spin-independent WIMP-nucleon, spin-dependent WIMP-neutron, and spin-dependent WIMP-proton cross sections for WIMP masses above 9 GeV/c^{2}. The most stringent limit is set for spin-independent scattering at 36 GeV/c^{2}, rejecting cross sections above 9.2×10^{-48} cm at the 90% confidence level.

Low-energy calibration of XENON1T with an internal ^{{textbf {37}}}Ar source

A low-energy electronic recoil calibration of XENON1T, a dual-phase xenon time projection chamber, with an internal {}^{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) photons/keV and (40.6,pm ,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}) electrons/keV. The {}^{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) 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}Ar can be considered as a regular calibration source for multi-tonne xenon detectors.

Simulation results for a low energy nuclear recoil yields measurement in liquid xenon using the MiX detector

Measuring the scintillation and ionization yields of liquid xenon in response to ultra-low energy nuclear recoil events is necessary to increase the sensitivity of liquid xenon experiments to light dark matter. Neutron capture on xenon can be used to produce nuclear recoil events with energies below 0.3 keVNR via the asymmetric emission of γ rays during nuclear de-excitation. The feasibility of an ultra-low energy nuclear recoil measurement using neutron capture was investigated for the Michigan Xenon (MiX) detector, a small dual-phase xenon time projection chamber that is optimized for a high scintillation gain. Simulations of the MiX detector, a partial neutron moderator, and a pulsed neutron generator indicate that a population of neutron capture events can be isolated from neutron scattering events. Further, the rate of neutron captures in the MiX detector was optimized by varying the thickness of the partial neutron moderator, neutron pulse width, and neutron pulse frequency.

Reduction of ^{222}hbox {Rn}-induced backgrounds in a hermetic dual-phase xenon time projection chamber

The continuous emanation of ^{222}hbox {Rn} from detector surfaces causes the dominant background in current liquid xenon time projection chambers (TPCs) searching for dark matter. A significant reduction is required for the next generation of detectors which are aiming to reach the neutrino floor, such as DARWIN. ^{222}hbox {Rn}-induced backgrounds can be reduced using a hermetic TPC, in which the sensitive target volume is mechanically separated from the rest of the detector containing the majority of Rn-emanating surfaces. We present a hermetic TPC that mainly follows the well-established design of leading xenon TPCs and has been operated successfully over a period of several weeks. By scaling up the results achieved to the DARWIN-scale, we show that the hermetic TPC concept can reduce the ^{222}hbox {Rn} concentration to the required level, even with imperfect separation of the volumes.

A machine learning-based methodology for pulse classification in dual-phase xenon time projection chambers

Machine learning techniques are now well established in experimental particle physics, allowing detector data to be analyzed in new and unique ways. The identification of signals in particle observatories is an essential data processing task that can potentially be improved using such methods. This paper aims at exploring the benefits that a dedicated machine learning approach might provide to the classification of signals in dual-phase noble gas time projection chambers. A full methodology is presented, from exploratory data analysis using Gaussian mixture models and feature importance ranking to the construction of dedicated predictive models based on standard implementations of neural networks and random forests, validated using unlabeled simulated data from the LZ experiment as a proxy to real data. The global classification accuracy of the predictive models developed in this work is estimated to be >99.0%, which is an improvement over conventional algorithms tested with similar data. The results from the clustering analysis were also used to identify anomalies in the data caused by miscalculated signal properties, showing that this methodology can also be used for data monitoring.

Performance of a radial time projection chamber with electroluminescence in liquid xenon

The dual-phase xenon time projection chamber (TPC) is a leading detector technology in rare event searches for dark matter and neutrino physics. The success of this type of detector technology relies on its capability to detect both primary scintillation and ionization signals from particle interactions in liquid xenon (LXe). The ionization electrons are converted into electroluminescence in the gas xenon (GXe), where a single electron can be amplified by more than 100 times in number of photons in a strong electric field. Maintaining a strong and uniform electric field in the small gas gap in large diameter TPCs is challenging. One alternative solution is to produce the electroluminescence in the LXe directly to overcome the gas gap uniformity problem. Here we report on the design and performance of a single-phase Radial TPC (RTPC) which can create and detect the electroluminescence directly in LXe. It simplifies the design and operation of the LXe TPC by using a single wire in the axial center to create the strong electric field. We present the performance of such an RTPC and discuss its limitations for potential applications.

Light yield and field dependence measurement in PandaX-II dual-phase xenon detector

The dual-phase xenon time projection chamber (TPC) is one of the most sensitive detector technology for dark matter direct search, where the energy deposition of incoming particle can be converted into photons and electrons through xenon excitation and ionization. The detector response to signal energy deposition varies significantly with the electric field in liquid xenon. We study the detector's light yield and its dependence on the electric field in the PandaX-II dual-phase detector containing 580 kg liquid xenon in the sensitive volume. From our measurements, the light yield at electric fields from 0 V/cm to 317 V/cm is obtained for energy depositions up to 236 keV.

Measurement of charge and light yields for Xe127 L -shell electron captures in liquid xenon

Dark matter searches using dual-phase xenon time-projection chambers (LXe-TPCs) rely on their ability to reject background electron recoils (ERs) while searching for signal-like nuclear recoils (NRs). ER response is typically calibrated using $\beta$-decay sources, such as tritium, but these calibrations do not characterize events accompanied by an atomic vacancy, as in solar neutrino scatters off inner shell electrons. Such events lead to emission of X-rays and Auger electrons, resulting in higher electron-ion recombination and thus a more NR-like response than inferred from $\beta$-decay calibration. We present a cross-calibration of tritium $\beta$-decays and $^{127}$Xe electron-capture decays (which produce inner-shell vacancies) in a small-scale LXe-TPC and give the most precise measurements to date of light and charge yields for the $^{127}$Xe L-shell electron-capture in liquid xenon. We observe a 6.9$\sigma$ (9.2$\sigma$) discrepancy in the L-shell capture response relative to tritium $\beta$-decays, measured at a drift field of 363 $\pm$ 14 V/cm (258 $\pm$ 13 V/cm), when compared to simulations tuned to reproduce the correct $\beta$-decay response. In dark matter searches, use of a background model that neglects this effect leads to overcoverage (higher limits) for background-only multi-kiloton-year exposures, but at a level much less than the 1-$\sigma$ experiment-to-experiment variation of the 90\% C.L. upper limit on the interaction rate of a 50 GeV/$c^2$ dark matter particle.

A measurement of the mean electronic excitation energy of liquid xenon

Detectors using liquid xenon as target are widely deployed in rare event searches. Conclusions on the interacting particle rely on a precise reconstruction of the deposited energy which requires calibrations of the energy scale of the detector by means of radioactive sources. However, a microscopic calibration, i.e. the translation from the number of excitation quanta into deposited energy, also necessitates good knowledge of the energy required to produce single scintillation photons or ionisation electrons in liquid xenon. The sum of these excitation quanta is directly proportional to the deposited energy in the target. The proportionality constant is the mean excitation energy and is commonly known as W-value. Here we present a measurement of the W-value with electronic recoil interactions in a small dual-phase xenon time projection chamber with a hybrid (photomultiplier tube and silicon photomultipliers) photosensor configuration. Our result is based on calibrations at mathcal {O}(1{-}10,{hbox {keV}}) with internal {^{37}hbox {Ar}} and {^{83text {m}}hbox {Kr}} sources and single electron events. We obtain a value of W={11.5}{} , ^{+0.2}_{-0.3} , mathrm {(syst.)} , hbox {eV}, with negligible statistical uncertainty, which is lower than previously measured at these energies. If further confirmed, our result will be relevant for modelling the absolute response of liquid xenon detectors to particle interactions.

The electric field dependence of single electron emission in the PIXeY two-phase xenon detector

Dual phase xenon detectors are widely used in experimental searches for galactic dark matter particles. The origin of single electron backgrounds following prompt scintillation and proportional scintillation signals in these detectors is not fully understood, although there has been progress in recent years. In this paper, we describe single electron backgrounds in 83mKr calibration events and their correlation with drift and extraction fields, using the Particle Identification in Xenon at Yale (PIXeY) dual-phase xenon time projection chamber. The single electron background induced by the Fowler-Nordheim (FN) effect is measured, and its electric field dependence is quantified. The photoionization of grids and impurities by prompt scintillation and proportional scintillation also contributes to the single electron background.

Design and production of the high voltage electrode grids and electron extraction region for the LZ dual-phase xenon time projection chamber

The dual-phase xenon time projection chamber (TPC) is a powerful tool for direct-detection experiments searching for WIMP dark matter, other dark matter models, and neutrinoless double-beta decay. Successful operation of such a TPC is critically dependent on the ability to hold high electric fields in the bulk liquid, across the liquid surface, and in the gas. Careful design and construction of the electrodes used to establish these fields is therefore required. We present the design and production of the LUX-ZEPLIN (LZ) experiment’s high-voltage electrodes, a set of four woven mesh wire grids. Grid design drivers are discussed, with emphasis placed on design of the electron extraction region. We follow this with a description of the grid production process and a discussion of steps taken to validate the LZ grids prior to integration into the TPC.

Development of a dual-phase xenon TPC with a quartz chamber for direct dark matter searches

Abstract The idea of a hermetic quartz chamber in a dual-phase xenon time projection chamber (TPC) has the potential to improve the detector sensitivity for direct dark matter searches in the future. A major challenge facing TPC detectors in future dark matter experiments will be the reduction of the internal background such as $^{222}$Rn and the deterioration of the ionization signal due to electronegative impurities. The hermetic quartz chamber can isolate the TPC’s sensitive volume from external interference and is thus expected to prevent contamination caused by radioactive and electronegative impurities, which originate from the outer detector materials. At the Kamioka Observatory in Japan, we have developed a TPC with a quartz chamber that contains a ⌀$ 48 \times 58$ mm volume of liquid xenon. At this development stage, we have not aimed for perfect hermeticity of the quartz chamber. Our aim here is twofold: first, to demonstrate via the use of a calibration source that the presence of quartz materials in the TPC does not impact its operation; and second, to perform quantitative measurements of the TPC’s characteristics. We successfully measured electron drift velocities of 1.2–1.7 mm/$\mu$s in liquid xenon under electric fields ranging from 75–384 V/cm, and also observed small S2 signals produced by a single ionized electron with a light yield of 16.5 $\pm$ 0.5 PE. These results were consistent with the expected values; therefore, our demonstrations provide a proof of principle for TPCs incorporating a quartz chamber.

Development and performance of high voltage electrodes for the LZ experiment

LZ is a next-generation dark matter search experiment designed to significantly extend our sensitivity to WIMP dark matter candidates. At the core of the LZ detector is a dual-phase xenon time projection chamber (TPC) with a 7-ton active mass. To observe signals from low-energy nuclear recoils, including WIMP-xenon scatters, four custom-woven wire-mesh grids of 1.5m diameter establish strong electric fields in the TPC to drift ionization electrons across the volume and extract them from the liquid surface. As a result of the high electric fields, dielectric breakdown between high voltage surfaces and spurious electron emission from regions of high surface fields are major concerns. To mitigate these risks, an R&D program exploring design geometry in high field regions, cleanliness procedures, and surface treatments has been carried out using a comprehensive suite of three mid-scale dual- and single-phase xenon detectors. These proceedings will summarize the design and construction of the LZ grids, and several aspects of the high voltage performance seen in the testing program.

Characterization of new photo-detectors for the future dark matter experiments with liquid xenon

In the last three decades, numerous terrestrial experiments were built to search for a faint interaction between Weakly Interacting Massive Particles (WIMP) and ordinary matter. Among them, experiments using dual-phase xenon time projection chambers (TPCs) are leading the search especially for high mass WIMPs. In these experiments, photomultipliers (PMTs) are used to detect the prompt primary scintillation and secondary electro-luminescence of ionized electrons generated following an interaction between WIMP and a Xe nucleus. However, PMTs have several important shortcomings: their residual radioactivity levels, cost, bulkiness, and stability at cryogenic temperatures. Therefore, several alternative technologies are under consideration toward future dark matter experiments using ~50 tons of liquid xenon (LXe). One such technology is silicon photomultipliers (SiPM). SiPM have very low radioactivity, compact geometry, low operation voltages and reasonable photo-detection efficiency for vacuum ultra violet (VUV) light. However, current SiPM still have ~two order of magnitude higher dark count rate compared to PMTs. In order to solve this problem, we are currently developing a new SiPM with the help of Hamamatsu. In this paper, we report the current status of the performance measurements of the new SiPM developed with Hamamatsu to improve the dark count rate (DCR).

Development of a tagged source of Pb-206 nuclei

There is a particular class of unavoidable backgrounds that plague low-background experiments and rare event searches, particularly those searching for nuclear recoil event signatures: decaying daughters of the 238U nuclear decay chain, which result from radon plate-out on detector materials. One such daughter isotope, 210Po, undergoes α-decay and produces a recoiling 103 keV 206Pb nucleus. To characterize this important background in the context of noble element detectors, we have implemented a triggered source for these 206Pb recoils in a dual-phase xenon time projection chamber (Xe TPC) within the Davis Xenon R&D testbed system (DAX). By adhering 210Po to the surface of a PIN diode and electrically floating the diode on the cathode of the TPC, we tag the α signals produced in the PIN diode and trigger on the correlated nuclear recoils in the liquid xenon (LXe). We discuss our methods for 210Po deposition, electronic readout of the PIN diode signals at high voltage, and analysis methods for event selection.

Search for bosonic super-WIMP interactions with the XENON100 experiment

We present results of searches for vector and pseudo-scalar bosonic super-WIMPs, which are dark matter candidates with masses at the keV-scale, with the XENON100 experiment. XENON100 is a dual-phase xenon time projection chamber operated at the Laboratori Nazionali del Gran Sasso. A profile likelihood analysis of data with an exposure of 224.6 live days $\times$ 34\,kg showed no evidence for a signal above the expected background. We thus obtain new and stringent upper limits in the $(8-125)$\,keV/c$^2$ mass range, excluding couplings to electrons with coupling constants of $g_{ae} > 3\times10^{-13}$ for pseudo-scalar and $\alpha'/\alpha > 2\times10^{-28}$ for vector super-WIMPs, respectively. These limits are derived under the assumption that super-WIMPs constitute all of the dark matter in our galaxy.

Search for magnetic inelastic dark matter with XENON100

We present the first search for dark matter-induced delayed coincidence signals in a dual-phase xenon time projection chamber, using the 224.6 live days of the XENON100 science run II. This very distinct signature is predicted in the framework of magnetic inelastic dark matter which has been proposed to reconcile the modulation signal reported by the DAMA/LIBRA collaboration with the null results from other direct detection experiments. No candidate event has been found in the region of interest and upper limits on the WIMP's magnetic dipole moment are derived. The scenarios proposed to explain the DAMA/LIBRA modulation signal by magnetic inelastic dark matter interactions of WIMPs with masses of 58.0 GeV/c2 and 122.7 GeV/c2 are excluded at 3.3 σ and 9.3 σ, respectively.