Dual-phase xenon time projection chamber (TPC) detectors offer heightened sensitivities for dark matter detection across a spectrum of particle masses. To broaden their capability to low-mass dark matter interactions, we investigated the light and charge responses of liquid xenon (LXe) to sub-keV nuclear recoils. Using neutron events from a pulsed Adelphi Deuterium-Deuterium neutron generator, an in situ calibration was conducted on the LUX detector. We demonstrate direct measurements of light and charge yields down to 0.45 keV and 0.27 keV, respectively, both approaching single quanta production, the physical limit of LXe detectors. These results hold significant implications for the future of dual-phase xenon TPCs in detecting low-mass dark matter via nuclear recoils.

The Migdal effect predicts that a nuclear recoil interaction can be accompanied by atomic ionization, allowing many dark matter direct detection experiments to gain sensitivity to sub-GeV masses. We report the first direct search for the Migdal effect for M- and L-shell electrons in liquid xenon using 7.0$\pm$1.6 keV nuclear recoils produced by tagged neutron scatters. Despite an observed background rate lower than that of expected signals in the region of interest, we do not observe a signal consistent with predictions. We discuss possible explanations, including inaccurate predictions for either the Migdal rate or the signal response in liquid xenon. We comment on the implications for direct dark-matter searches and future Migdal characterization efforts.

Eos is a technology demonstrator, designed to explore the capabilities of hybrid event detection technology, leveraging both Cherenkov and scintillation light simultaneously. With a fiducial mass of four tons, Eos is designed to operate in a high-precision regime, with sufficient size to utilize time-of-flight information for full event reconstruction, flexibility to demonstrate a range of cutting edge technologies, and simplicity of design to facilitate potential future deployment at alternative sites. Results from Eos can inform the design of future neutrino detectors for both fundamental physics and nonproliferation applications. This paper describes the conceptual design and potential applications of the Eos detector.

We investigate a hypothesis that energy accumulation and the subsequent release in NaI(Tl) may lead to pulse-like events in the few-keV energy regime, a phenomenon suggested by the crystal manufacturing company Saint-Gobain, who provided the crystals for DAMA-LIBRA. While we observed delayed long-lasting light emission in a 3" NaI(Tl) crystal after exposing it to UV light, the delayed light consists primarily of single photons that are uncorrelated with each other. We also observe delayed light emission in NaI(Tl) following gamma radiation and large ionization events like cosmic-ray muons. We found that irradiating the crystal with red light after UV exposure significantly suppressed delayed photon emissions.

To date, antineutrino experiments built for the purpose of demonstrating a nonproliferation capability have typically employed organic scintillators, were situated as close to the core as possible -typically a few meters to tens of meters distant and have not exceeded a few tons in size. One problem with this approach is that proximity to the reactor core require accommodation by the host facility. Water Cherenkov detectors located offsite, at distances of a few kilometers or greater, may facilitate non-intrusive monitoring and verification of reactor activities over a large area. As the standoff distance increases, the detector target mass must scale accordingly. This article quantifies the degree to which a kiloton-scale gadolinium-doped water-Cherenkov detector can exclude the existence of undeclared reactors within a specified distance, and remotely detect the presence of a hidden reactor in the presence of declared reactors, by verifying the operational power and standoff distance using a Feldman-Cousins based likelihood analysis. A 1-kton scale (fiducial) water Cherenkov detector can exclude gigawatt-scale nuclear reactors up to tens of kilometers within a year. When attempting to identify the specific range and power of a reactor, the detector energy resolution was not sufficient to delineate between the two.

Measurements of the optical properties of highly transparent liquids are necessary for large-scale detectors that seek to detect optical signatures in kiloton-scale or larger volumes. Detailed understanding of the attenuation and scattering properties of fill media is critical to the ability to accurately simulate detector performance, and yet is often unavailable until in-situ measurements can be performed. Moreover, in-situ measurements may rely on effective attenuation lengths or other approximations to characterize performance, rather than absolute measurements of attenuation and scattering. To better understand the optical properties of potential fill media and purification schemes, a system has been developed which provides simultaneous attenuation and differential scattering cross-section measurements for highly transparent liquids. This horizontal, adjustable path-length “long-arm” system provides excellent isolation from the atmosphere, a high degree of vibration insensitivity, and a simple and reliable method of calibration. Further, scattering measurements can be carried out simultaneously at ports along the beamline equipped with optics allowing the selection of scatter angle and polarization. This enables both reliable quantitative scatter measurements and phase-function separation. This system has been extensively tested using deionized (DI) water as a benchmark, and has demonstrated repeatable measurements of attenuation lengths exceeding 100 m and scattering lengths approaching 1 km.

Photomultiplier tubes (PMTs) are traditionally an integral part of large underground experiments as they measure the light emission from particle interactions within the enclosed detection media. The BUTTON experiment will utilise around 100 PMTs to measure the response of different media suitable for rare event searches. A subset of low-radioactivity 10-inch Hamamatsu R7081 PMTs were tested, characterised, and compared to manufacture certification. This manuscript describes the laboratory tests and analysis of gain, peak-to-valley ratio and dark rate of the PMTs to give an understanding of the charge response, signal-to-noise ratio and dark noise background as an acceptance test of the suitability of these PMTs for water-based detectors. Following the evaluation of these tests, the PMT performance agreed with the manufacturer specifications. These results are imperative for modeling the PMT response in detector simulations and providing confidence in the performance of the devices once installed in the detector underground.

Liquid xenon-based direct detection dark matter experiments have recently expanded their searches to include high-energy nuclear recoil events as motivated by effective field theory dark matter and inelastic dark matter interaction models, but few xenon recoil calibrations above 100 keV are currently available. In this work, we measured the scintillation and ionization yields of xenon recoils up to 426 keV. The experiment uses 14.1 MeV neutrons to scatter off xenon in a compact liquid xenon time projection chamber and produce quasi-monoenergetic xenon recoils between 39 keV and 426 keV. We report the xenon recoil responses and their electric field-dependence for recoil energies up to 306 keV; due to the low event statistics and the relatively mild field dependence, the yield values at higher energies are reported as the average of xenon responses for electric fields between 0.2-2.0 kV/cm. This result will enable xenon-based dark matter experiments to significantly increase their high energy dark matter sensitivities by including energy regions that were previously inaccessible due to lack of calibrations.

Detection of light signals is crucial to a wide range of particle detectors. In particular, efficient detection of vacuum ultraviolet (VUV) light will provide new opportunities for some novel detectors currently being developed, but is technically challenging. In this article, we characterized the performance of Hamamatsu VUV4 silicon photomultipliers (SiPMs) for detecting VUV argon scintillation light without wavelength shifting. Using a customized cryogenic amplifier design, we operated two models of VUV4 SiPMs inside liquid argon and thoroughly examined their direct sensitivities to liquid argon scintillation. In addition to describing their cryogenic performance, we measured a photon detection efficiency of $14.7^{+1.1}_{-2.4}$% and $17.2^{+1.6}_{-3.0}$% at 128 nm for these two VUV4 models for operation at 4 V of overvoltage, with the main uncertainty arising from the SiPM reflectivity for VUV light.

nuclear wastes. In the arms control area, this method can be used as a part of warhead dismantlement measurements to confirm separation of components, and may be applicable in warhead confirmation. In the context of emergency response, it can be used for detailed diagnostics of an unknown item. At present, the delayed gamma-ray assay technology reliably qualifies for the Technical Readiness Level 3 (TRL 3). The R&D work completed under this project has successfully demonstrated the empirical proof-of-concept for this active interrogation technology for a variety of measurement configurations, neutron sources, and nuclear material samples. A robust first-principles analytical signature modeling methodology was developed, experimentally validated, and can be easily extrapolated to a range of realistic measurement scenarios. Several response analysis methodologies have been implemented and deemed reliable for a variety of active interrogation applications in the areas of nuclear material safeguards, arms control, and emergency response. The initial readiness level before the start of this project was assessed at TRL 0, since only fragmentary records of the signature observations and speculative statements of the relevant non-destructive assay applications existed at that time. The delayed gamma-ray technology readiness can be easily advanced to TRL 4 in a short period, if a certain measurement application is specified and set for a demonstration in a laboratory environment. The critical hardware components of the delayed gamma-ray measurement technology (neutron generators, gamma-ray spectrometers) are readily available as COTS and can be configured for a specific deployment configuration. The primary risk of the delayed gamma-ray assay methodology is defined by the applicationspecific uncertainties. Evaluation of the system performance can be effectively completed once the expected measurement purpose, nuclear material characteristics, dimensions, and radiation exposure constraints are specified. A minor risk can be associated with the delayed gamma-ray response analysis techniques. Several approaches were proposed and demonstrated primarily using the modeled signatures. The observed performance may not be easily transferrable to the conditions of a real measurement setup, and some additional R&D may be required. Overall, the delayed gamma-ray assay technology can be recommended for follow-up demonstrations addressing relevant measurement applications in the areas of nuclear material safeguards, arms control, and emergency response.

Theia would be a novel, "hybrid" optical neutrino detector, with a rich physics program. This paper is intended to provide a brief overview of the concepts and physics reach of Theia. Full details can be found in the Theia white paper [1].

EOS is a technology demonstrator, designed to explore the capabilities of hybrid event detection technology, leveraging both Cherenkov and scintillation light simultaneously. With a fiducial mass of four tons, EOS is designed to operate in a high-precision regime, with sufficient size to utilize time-of-flight information for full event reconstruction, flexibility to demonstrate a range of cutting edge technologies, and simplicity of design to facilitate potential future deployment at alternative sites. Results from EOS can inform the design of future neutrino detectors for both fundamental physics and nonproliferation applications.

The High Energy Physics community can benefit from a natural synergy in research activities into next-generation large-scale water and scintillator neutrino detectors, now being studied for remote reactor monitoring, discovery and exclusion applications in cooperative nonproliferation contexts. Since approximately 2010, US nonproliferation researchers, supported by the National Nuclear Security Administration (NNSA), have been studying a range of possible applications of relatively large (100 ton) to very large (hundreds of kiloton) water and scintillator neutrino detectors. In parallel, the fundamental physics community has been developing detectors at similar scales and with similar design features for a range of high-priority physics topics, primarily in fundamental neutrino physics. These topics include neutrino oscillation studies at beams and reactors, solar, and geological neutrino measurements, supernova studies, and others. Examples of ongoing synergistic work at U.S. national laboratories and universities include prototype gadolinium-doped water and water-based and opaque scintillator test-beds and demonstrators, extensive testing and industry partnerships related to large area fast position-sensitive photomultiplier tubes, and the development of concepts for a possible underground kiloton-scale water-based detector for reactor monitoring and technology demonstrations. Some opportunities for engagement between the two communities include bi-annual Applied Antineutrino Physics conferences, collaboration with U.S. National Laboratories engaging in this research, and occasional NNSA funding opportunities supporting a blend of nonproliferation and basic science R&D, directed at the U.S. academic community.

We present the results from combining machine learning with the profile likelihood fit procedure, using data from the Large Underground Xenon (LUX) dark matter experiment. This approach demonstrates reduction in computation time by a factor of 30 when compared with the previous approach, without loss of performance on real data. We establish its flexibility to capture nonlinear correlations between variables (such as smearing in light and charge signals due to position variation) by achieving equal performance using pulse areas with and without position-corrections applied. Its efficiency and scalability furthermore enables searching for dark matter using additional variables without significant computational burden. We demonstrate this by including a light signal pulse shape variable alongside more traditional inputs, such as light and charge signal strengths. This technique can be exploited by future dark matter experiments to make use of additional information, reduce computational resources needed for signal searches and simulations, and make inclusion of physical nuisance parameters in fits tractable.

This article describes the setup and performance of the near and far detectors in the Double Chooz experiment. The electron antineutrinos of the Chooz nuclear power plant were measured in two identically designed detectors with different average baselines of about 400 m and 1050 m from the two reactor cores. Over many years of data taking the neutrino signals were extracted from interactions in the detectors with the goal of measuring a fundamental parameter in the context of neutrino oscillation, the mixing angle θ13. The central part of the Double Chooz detectors was a main detector comprising four cylindrical volumes filled with organic liquids. From the inside towards the outside there were volumes containing gadolinium-loaded scintillator, gadolinium-free scintillator, a buffer oil and, optically separated, another liquid scintillator acting as veto system. Above this main detector an additional outer veto system using plastic scintillator strips was installed. The technologies developed in Double Chooz were inspiration for several other antineutrino detectors in the field. The detector design allowed implementation of efficient background rejection techniques including use of pulse shape information provided by the data acquisition system. The Double Chooz detectors featured remarkable stability, in particular for the detected photons, as well as high radiopurity of the detector components.

The LUX-ZEPLIN dark matter search aims to achieve a sensitivity to the WIMP-nucleon spin-independent cross-section down to (1-2)x10(-12) pb at a WIMP mass of 40 GeV/c(2). This paper describes the simulations framework that, along with radioactivity measurements, was used to support this projection, and also to provide mock data for validating reconstruction and analysis software. Of particular note are the event generators, which allow us to model the background radiation, and the detector response physics used in the production of raw signals, which can be converted into digitized waveforms similar to data from the operational detector. Inclusion of the detector response allows us to process simulated data using the same analysis routines as developed to process the experimental data. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved.

We report here the results of a nonrelativistic effective field theory (EFT) WIMP search analysis using LUX data. We build upon previous LUX analyses by extending the search window to include nuclear recoil energies up to ∼ 180 keV nr , requiring a reassessment of data quality criteria and background models. In order to use an unbinned profile likelihood statistical framework, the development of new analysis techniques to account for higher-energy backgrounds was required. With a 3 . 14 × 10 4 kg · day exposure using data collected between 2014 and 2016, we find our data is compatible with the background expectation and set 90% C.L. exclusion limits on nonrelativistic EFT WIMP-nucleon couplings, improving upon previous LUX results and providing constraints on a EFT WIMP interactions using the f neutron ; proton g interaction basis. Additionally, we report exclusion limits on inelastic EFT WIMP-isoscalar recoils that are competitive and world-leading for several interaction operators.

The projected sensitivity of the LUX-ZEPLIN (LZ) experiment to two-neutrino and neutrinoless double β decay of 134 Xe is presented. LZ is a 10-tonne xenon time-projection chamber optimized for the detection of dark matter particles and is expected to start operating in 2021 at Sanford Underground Research Facility, USA. Its large mass of natural xenon provides an exceptional opportunity to search for the double β decay of 134 Xe, for which xenon detectors enriched in 136 Xe are less effective. For the two-neutrino decay mode, LZ is predicted to exclude values of the half-life up to 1 . 7 × 10 24 years at 90% confidence level (CL) and has a three-sigma observation potential of 8 . 7 × 10 23 years, approaching the predictions of nuclear models. For the neutrinoless decay mode LZ, is projected to exclude values of the half-life up to 7 . 3 × 10 24 years at 90% CL.

D.S. Akerib, 2 A.K. Al Musalhi, S.K. Alsum, C.S. Amarasinghe, A. Ames, 2 T.J. Anderson, 2 N. Angelides, H.M. Araújo, J.E. Armstrong, M. Arthurs, X. Bai, J. Balajthy, S. Balashov, J. Bang, J.W. Bargemann, D. Bauer, A. Baxter, P. Beltrame, E.P. Bernard, 16 A. Bernstein, A. Bhatti, A. Biekert, 16 T.P. Biesiadzinski, 2 H.J. Birch, G.M. Blockinger, B. Boxer, C.A.J. Brew, P. Brás, S. Burdin, J.K. Busenitz, M. Buuck, 2 R. Cabrita, M.C. Carmona-Benitez, M. Cascella, C. Chan, N.I. Chott, A. Cole, M.V. Converse, A. Cottle, 23 G. Cox, J.E. Cutter, C.E. Dahl, 23 L. de Viveiros, J.E.Y. Dobson, E. Druszkiewicz, S.R. Eriksen, A. Fan, 2 S. Fayer, N.M. Fearon, S. Fiorucci, H. Flaecher, E.D. Fraser, T. Fruth, R.J. Gaitskell, J. Genovesi, C. Ghag, E. Gibson, S. Gokhale, M.G.D. van der Grinten, C.B. Gwilliam, C.R. Hall, S.J. Haselschwardt, S.A. Hertel, M. Horn, D.Q. Huang, C.M. Ignarra, 2 O. Jahangir, R.S. James, W. Ji, 2 J. Johnson, A.C. Kaboth, 11 A.C. Kamaha, K. Kamdin, 15 K. Kazkaz, D. Khaitan, A. Khazov, I. Khurana, D. Kodroff, L. Korley, E.V. Korolkova, H. Kraus, S. Kravitz, L. Kreczko, B. Krikler, V.A. Kudryavtsev, E.A. Leason, K.T. Lesko, C. Levy, J. Li, J. Liao, J. Lin, 16 A. Lindote, R. Linehan, 2 W.H. Lippincott, 23 X. Liu, M.I. Lopes, E. Lopez Asamar, B. López Paredes, ∗ W. Lorenzon, S. Luitz, P.A. Majewski, A. Manalaysay, L. Manenti, R.L. Mannino, N. Marangou, M.E. McCarthy, D.N. McKinsey, 16 J. McLaughlin, E.H. Miller, 2 E. Mizrachi, 8 A. Monte, 23 M.E. Monzani, 2 J.A. Morad, J.D. Morales Mendoza, 2 E. Morrison, B.J. Mount, A.St.J. Murphy, D. Naim, A. Naylor, C. Nedlik, H.N. Nelson, F. Neves, J.A. Nikoleyczik, I. Olcina, 16 K.C. Oliver-Mallory, S. Pal, K.J. Palladino, 4 J. Palmer, N. Parveen, E.K. Pease, B. Penning, G. Pereira, A. Piepke, Y. Qie, J. Reichenbacher, C.A. Rhyne, A. Richards, Q. Riffard, 16 G.R.C. Rischbieter, R. Rosero, P. Rossiter, D. Santone, A.B.M.R. Sazzad, R.W. Schnee, P.R. Scovell, S. Shaw, T.A. Shutt, 2 J.J. Silk, C. Silva, R. Smith, 16 M. Solmaz, V.N. Solovov, P. Sorensen, I. Stancu, A. Stevens, K. Stifter, 2 B. Suerfu, 16 T.J. Sumner, N. Swanson, M. Szydagis, W.C. Taylor, R. Taylor, D.J. Temples, P.A. Terman, D.R. Tiedt, M. Timalsina, W.H. To, 2 M. Tripathi, D.R. Tronstad, W. Turner, U. Utku, A. Vaitkus, B. Wang, J.J. Wang, W. Wang, 27 J.R. Watson, 16 R.C. Webb, R.G. White, 2 T.J. Whitis, 1 M. Williams, F.L.H. Wolfs, D. Woodward, C.J. Wright, X. Xiang, J. Xu, M. Yeh, and P. Zarzhitsky SLAC National Accelerator Laboratory, Menlo Park, CA 94025-7015, USA Kavli Institute for Particle Astrophysics and Cosmology,

This paper presents a novel technique for mitigating electrode backgrounds that limit the sensitivity of searches for low-mass dark matter (DM) using xenon time projection chambers. In the Large Underground Xenon (LUX) detector, signatures of low-mass DM interactions would be very low-energy (similar to keV) scatters in the active target that ionize only a few xenon atoms and seldom produce detectable scintillation signals. In this regime, extra precaution is required to reject a complex set of low-energy electron backgrounds that have long been observed in this class of detector. Noticing backgrounds from the wire grid electrodes near the top and bottom of the active target are particularly pernicious, we develop a machine learning technique based on ionization pulse shape to identify and reject these events. We demonstrate the technique can improve Poisson limits on low-mass DM interactions by a factor of 1.7-3 with improvement depending heavily on the size of ionization signals. We use the technique on events in an effective 5 tonne.day exposure from LUX's 2013 science operation to place strong limits on low-mass DM particles with masses in the range m(chi) is an element of 0.15-10 GeV. This machine learning technique is expected to be useful for near-future experiments, such as LUX-ZEPLIN and XENONnT, which hope to perform low-mass DM searches with the stringent background control necessary to make a discovery.