Liquid Xenon Detector Research Articles

First Indication of Solar B8 Neutrinos through Coherent Elastic Neutrino-Nucleus Scattering in PandaX-4T

The PandaX-4T liquid xenon detector at the China Jinping Underground Laboratory is used to measure the solar B8 neutrino flux by detecting neutrinos through coherent scattering with xenon nuclei. Data samples requiring the coincidence of scintillation and ionization signals (paired), as well as unpaired ionization-only signals (US2), are selected with energy threshold of approximately 1.1 keV (0.33 keV) nuclear recoil energy. Combining the commissioning run and the first science run of PandaX-4T, a total exposure of 1.20 and 1.04 tonne·year are collected for the paired and US2, respectively. After unblinding, 3 and 332 events are observed with an expectation of 2.8±0.5 and 251±32 background events, for the paired and US2 data, respectively. A combined analysis yields a best-fit B8 neutrino signal of 3.5 (75) events from the paired (US2) data sample, with ∼37% uncertainty, and the background-only hypothesis is disfavored at 2.64σ significance. This gives a solar B8 neutrino flux of (8.4±3.1)×106 cm−2 s−1, consistent with the standard solar model prediction. It is also the first indication of solar B8 neutrino “fog” in a dark matter direct detection experiment. Published by the American Physical Society 2024

A neutrino floor for the Migdal effect

Neutrino-nucleus scatterings in the detector could induce electron ionization signatures due to the Migdal effect. We derive prospects for a future detection of the Migdal effect via coherent elastic solar neutrino-nucleus scatterings in liquid xenon detectors, and discuss the irreducible background that it constitutes for the Migdal effect caused by light dark matter-nucleus scatterings. Furthermore, we explore the ionization signal induced by some neutrino electromagnetic and non-standard interactions on nuclei. In certain scenarios, we find a distinct peak on the ionization spectrum of xenon around 0.1 keV, in clear contrast to the Standard Model expectation.

LUX, ZEPLIN and LUX-ZEPLIN: Developments in liquid xenon detectors and the search for WIMP dark matter

The search for dark matter in the form of Weakly Interacting Massive Particles (WIMPs) remains one of the enduring scientific and technical challenges in physics despite four decades of research. A discovery would have broad implications for particle physics, astrophysics, and cosmology. Over the last 15 years, liquid xenon time projection chambers have been on the forefront of this search, starting with detector masses on the 10-kg scale and now reaching the 10-tonne scale. Advances in a number of technical areas across xenon-detector collaborations worldwide, along with progress in related techniques in low-background and liquid noble detectors, have led to significant and steady improvements in sensitivity. In this contribution to Nobel Symposium 182, I highlight several of the contributions made by the LUX, ZEPLIN, and LUX-ZEPLIN (LZ) collaborations, and members thereof. I also discuss briefly the status of the currently-operating and world-leading LZ experiment.

PANCAKE: a large-diameter cryogenic test platform with a flat floor for next generation multi-tonne liquid xenon detectors

The PANCAKE facility is the world's largest liquid xenon test platform.Inside its cryostat with an internal diameter of 2.75 m, components for the next generation of liquid xenon experiments, such as DARWIN or XLZD, will be tested at their full scale.This is essential to ensure their successful operation.This work describes the facility, including its cryostat, cooling systems, xenon handling infrastructure, and its monitoring and instrumentation.The inner vessel has a flat floor, which allows the full diameter to be used with a modest amount of xenon.This is a novel approach for such a large cryostat and is of interest for future large-scale experiments, where a standard torispherical head would require tonnes of additional xenon.Our current xenon inventory of 400 kg allows a liquid depth of about 2 cm in the inner cryostat vessel.We also describe the commissioning of the facility, which is now ready for component testing.

Challenges for dark matter direct search with SiPMs

Liquid xenon and liquid argon detectors are leading the direct dark matter search and are expected to be the candidate technology for the forthcoming generation of ultra-sensitive large-mass detectors. At present, scintillation light detection in those experiments is based on ultra-pure low-noise photo-multipliers. To overcome the issues in terms of the extreme radio-purity, costs, and technological feasibility of the future dark matter experiments, the novel silicon photomultiplier (SiPM)-based photodetector modules seem to be promising candidates, capable of replacing the present light detection technology. However, the intrinsic features of SiPMs may limit the present expectations. In particular, interfering phenomena, especially related to the optical correlated noise, can degrade the energy and pulse shape resolutions. As a consequence, the projected sensitivity of the future detectors has to be reconsidered accordingly.

Characterization of a 220Rn source for low-energy electronic recoil calibration of the XENONnT detector

Low-background liquid xenon detectors are utilized in the investigation of rare events, including dark matter and neutrinoless double beta decay. For their calibration, gaseous 220Rn can be used. After being introduced into the xenon, its progeny isotope 212Pb induces homogeneously distributed, low-energy (<30 keV) electronic recoil interactions. We report on the characterization of such a source for use in the XENONnT experiment. It consists of four commercially available 228Th sources with an activity of 55 kBq. These sources provide a high 220Rn emanation rate of about 8 kBq. We find no indication for the release of the long-lived 228Th above 1.7 mBq. Though an unexpected 222Rn emanation rate of about 3.6 mBq is observed, this source is still in line with the requirements for the XENONnT experiment.

Search for Light Dark Matter with Ionization Signals in the PandaX-4T Experiment.

We report the search results of light dark matter through its interactions with shell electrons and nuclei, using the commissioning data from the PandaX-4T liquid xenon detector. Low energy events are selected to have an ionization-only signal between 60 to 200 photoelectrons, corresponding to a mean nuclear recoil energy from 0.77 to 2.54keV and electronic recoil energy from 0.07 to 0.23keV. With an effective exposure of 0.55 tonne·year, we set the most stringent limits within a mass range from 40 MeV/c^{2} to 10 GeV/c^{2} for pointlike dark matter-electron interaction, 100 MeV/c^{2} to 10 GeV/c^{2} for dark matter-electron interaction via a light mediator, and 3.2 to 4 GeV/c^{2} for dark matter-nucleon spin-independent interaction. For DM interaction with electrons, our limits are closing in on the parameter space predicted by the freeze-in and freeze-out mechanisms in the early Universe.

First results on FHM — a Floating Hole Multiplier

A proof of principle of a novel concept for event recording in dual-phase liquid xenon detectors — the Floating Hole Multiplier (FHM) — is presented. It is shown that a standard Thick Gaseous Electron Multiplier (THGEM), freely floating on the liquid xenon surface permits extraction of electrons from the liquid to the gas. Secondary scintillation induced by the extracted electrons in the THGEM holes as well as in the uniform field above it was observed. The first results with the FHM indicate that the concept of floating electrodes may offer new prospects for large-scale dual-phase detectors, for dark matter searches in particular.

The XeBRA platform for liquid xenon time projection chamber development

XeBRA is a flexible cryogenic platform designed to perform research and development for liquid xenon detectors searching for rare events. Its extra-large outer cryostat makes it possible to install a wide variety of detector designs. We present the system, including its cryogenic, gas handling, data acquisition and slow control subsystems. Two dual phase time projection chambers with sensitive masses at the 1 kg scale have so far been operated in XeBRA. Using data from these, we determine the field-dependence of the electron drift velocity in liquid xenon. We also measure the relative charge and light yields for 41.5 keV energy deposits from 83mKr with electric drift fields between 50 V/cm and 677 V/cm.

Design, construction and commissioning of a high-flow radon removal system for XENONnT

A high-flow radon removal system based on cryogenic distillation was developed and constructed to reduce radon-induced backgrounds in liquid xenon detectors for rare event searches such as XENONnT. A continuous purification of the XENONnT liquid xenon inventory of 8.4 tonnes at process flows up to 71 kg/h (200 slpm) is required to achieve a radon reduction by a factor larger than two for radon sources inside the detector. To reach such high flows, the distillation column’s design features liquid xenon inlet and outlets along with novel custom-made bath-type heat exchangers with high liquefaction capabilities. The distillation process was designed using a modification of the McCabe–Thiele approach without a bottom product extraction. The thermodynamic concept is based on a Clausius–Rankine cooling cycle with phase-changing medium, in this case the xenon itself. To drastically reduce the external cooling power requirements, an energy efficient heat pump concept was developed applying a custom-made four cylinder magnetically-coupled piston pump as compressor. The distillation system was operated at thermodynamically stable conditions at a process flow of ({91pm 2}),mathrm{kg/h} ((258pm 6) slpm), 30% over design. With this flow, a activity concentration <1,upmu Bq/kg is expected inside the XENONnT detector given the measured radon source distribution.

Commissioning of liquid xenon gamma-ray detector for MEG II experiment

The liquid xenon (LXe) gamma-ray detector in the MEG II experiment measures the energy, position and timing of the gamma-ray from μ+→e+γ, and it is the key to the unprecedented sensitivity of the experiment. All the photo sensors of 4092 VUV MPPCs and 668 PMTs were read out for the first time and a physics data collection started in 2021. The detector response was monitored all through the beam time, and the LXe detector operated stably. The timing and energy resolution were measured using the gamma-rays from the π0 decays after charge exchange reaction of charged pions in a liquid hydrogen target. The detector has been successfully commissioned and is ready for the long physics run.

The liquid xenon detector for the MEG II experiment to detect 52.8 MeV [formula omitted] with large area VUV-sensitive MPPCs

The MEG II experiment is searching for new physics beyond the SM (e.g. SUSY-GUT, SUSY-seesaw) through the lepton flavor violating μ+→e+γ decay with ten times better sensitivity than the MEG experiment. The MEG collaboration published the result of B(μ+→e+γ)<4.2×10−13 at 90% C.L. in 2016, which was thirty times better result than the previous limit. As the sensitivity of the MEG experiment was already limited by the accidental background, the MEG detector had to be upgraded to reach one order of magnitude better sensitivity. The MEG experiment utilized 846 2 inch PMTs to detect scintillation light in a 900 l liquid xenon γ calorimeter. In the MEG II experiment, 216 2 inch PMTs on the γ incident face were replaced with 4092 MPPCs (SiPMs produced by Hamamatsu) to improve the energy and position resolutions. We started the detector commissioning with the full electronics readout channels for the first time in 2021, and soon after, we started the physics data taking. Here the LXe detector status including initial photon sensor calibration and performance will be summarized together with the expected detector performance. The PDE decrease of the SiPM observed in the high rate muon beam environment and our possible remedy will also be discussed.

An approximate likelihood for nuclear recoil searches with XENON1T data

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.

Liquid-phase purification for multi-tonne xenon detectors

As liquid xenon detectors grow in scale, novel techniques are required to maintain sufficient purity for charges to survive across longer drift paths. The Xeclipse facility at Columbia University was built to test the removal of electronegative impurities through cryogenic filtration powered by a liquid xenon pump, enabling a far higher mass flow rate than gas-phase purification through heated getters. In this paper, we present results from Xeclipse, including measured oxygen removal rates for two sorbent materials, which were used to guide the design and commissioning of the XENONnT liquid purification system. Thanks to this innovation, XENONnT has achieved an electron lifetime greater than {10},hbox {ms} in an sim {8.6}{text {tonne}} total mass, perhaps the highest purity ever measured liquid xenon detector.

Inelastic charged-current interactions of supernova neutrinos in two-phase liquid xenon dark matter detectors

It is known that neutrinos from supernova (SN) bursts can potentially give rise to nuclear recoil (NR) signals arising from the neutral current (NC) process of coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$) interactions of the neutrinos with xenon nuclei in future, large (multiton scale) liquid xenon (LXe) detectors employed for dark matter searches, depending on the SN progenitor mass and distance to the SN. In this paper, we show that the same detectors will also be sensitive to inelastic charged-current (CC) interactions of the SN electron neutrinos (${\ensuremath{\nu}}_{e}\mathrm{CC}$) with xenon nuclei. Such interactions, while creating an electron in the final state, also leave the postinteraction target nucleus in an excited state, the subsequent deexcitation of which produces, among other particles, $\ensuremath{\gamma}$ rays and neutrons. The electron and deexcitation $\ensuremath{\gamma}$ rays will give ``electron recoil'' (ER) type signals, while the deexcitation neutrons---the so-called ``neutrino-induced neutrons'' (${\ensuremath{\nu}}_{e}\mathrm{In}$)---produce, through their multiple scattering on the xenon nuclei, further xenon nuclear recoils that will also give NR signals (in addition to those produced through the $\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$ interactions). We discuss the observable scintillation and ionization signals associated with SN neutrino-induced $\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$ and ${\ensuremath{\nu}}_{e}\mathrm{CC}$ events in a generic LXe detector and argue that upcoming, sufficiently large LXe detectors should be able to detect both these types of events due to neutrinos from reasonably close-by SN bursts. We also note that since the total CC-induced ER and NR signals receive contributions predominantly from ${\ensuremath{\nu}}_{e}\mathrm{CC}$ interactions while the $\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$ contribution comes from NC interactions of all six species of neutrinos, identification of the ${\ensuremath{\nu}}_{e}\mathrm{CC}$ and $\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$ origin events may offer the possibility of extracting useful information about the distribution of the total SN explosion energy going into different neutrino flavors.

Study of background from accidental coincidence signalsin the PandaX-II experiment* *Supported in part by a grant from the Ministry of Science and Technology of China (2016YFA0400301), National Science Foundation of China (12090060, 12005131, 11905128, 11925502, 11775141), and Office of Science and Technology, Shanghai Municipal Government (18JC1410200)

The PandaX-II experiment employed a 580kg liquid xenon detector to search for the interactions between dark matter particles and the target xenon atoms. The accidental coincidences of isolated signals result in a dangerous background which mimic the signature of the dark matter. We performed a detailed study on the accidental coincidence background in PandaX-II, including the possible origin of the isolated signals, the background level and corresponding background suppression method. With a boosted-decision-tree algorithm, the accidental coincidence background is reduced by 70% in the dark matter signal region, thus the sensitivity of dark matter search at PandaX-II is improved.

Feasibility study to use neutron capture for an ultralow energy nuclear-recoil calibration in liquid xenon

The feasibility of an ultra-low energy nuclear-recoil measurement in liquid xenon using neutron capture is investigated for a small (sub-kilogram) liquid xenon detector that is optimized for a high scintillation gain, and a pulsed neutron source. The measurement uses the recoil energies imparted to xenon nuclei during the de-excitation process following neutron capture, where promptly emitted $\gamma$ cascades can provide the nuclei with up to $0.3$ keV$_\text{nr}$ of recoil energy due to conservation of momentum. A successful calibration of scintillation photon and ionization electron yields below this energy will contribute to a greater sensitivity for liquid xenon experiments in searches for light WIMPs.

Search for neutrinoless quadruple beta decay of 136Xe in XMASS-I

A search for the neutrinoless quadruple beta decay of 136Xe was conducted with the liquid-xenon detector XMASS-I using 327 kg ×800.0 days of the exposure. The pulse shape discrimination based on the scintillation decay time constant which distinguishes γ-rays including the signal and β-rays was used to enhance the search sensitivity. No significant signal excess was observed from the energy spectrum fitting with precise background evaluation, and we set a lower limit of the half life of 3.7 × 1024 years at 90% confidence level. This is the first experimental constraint of the neutrinoless quadruple beta decay of 136Xe.

GPU-based optical simulation of the DARWIN detector

Understanding propagation of scintillation light is critical for maximizing the discovery potential of next-generation liquid xenon detectors that use dual-phase time projection chamber technology. This work describes a detailed optical simulation of the DARWIN detector implemented using Chroma, a GPU-based photon tracking framework. To evaluate the framework and to explore ways of maximizing efficiency and minimizing the time of light collection, we simulate several variations of the conventional detector design. Results of these selected studies are presented. More generally, we conclude that the approach used in this work allows one to investigate alternative designs faster and in more detail than using conventional Geant4 optical simulations, making it an attractive tool to guide the development of the ultimate liquid xenon observatory.

A LN2-based cryogenic system prototype for future PandaX experiment

This paper describes results on R&D of an economical and efficient cryogenic system prototype for future liquid xenon detector. The test module of the prototype has a “coldhead” attached to a copper rod, which is specially designed to transport heat loads to a free-boiling liquid nitrogen bath. The performance of the test module and commercial refrigerators is compared. The module with an optimized copper rod has demonstrated more than 1500 W cooling power at 178 K. The temperature of the “cold head” can be kept stable with an error of 0.02 K, its fluctuation is within 0.1 K.