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.

This paper will discuss the microphysical simulation of interactions in liquid xenon, the active detector medium in many leading rare-event searches for new physics, and describe experimental observables useful for understanding detector performance. The scintillation and ionization yield distributions for signal and background will be presented using the Noble Element Simulation Technique (NEST), which is a toolkit based on experimental data and simple, empirical formulae, which mimic previous microphysics modeling, but are guided by data. The NEST models for light and charge production as a function of the particle type, energy, and electric field will be reviewed, as well as models for energy resolution and final pulse areas. NEST will be compared to other models or sets of models, and vetted against real data, with several specific examples pulled from XENON, ZEPLIN, LUX, LZ, PandaX, and table-top experiments used for calibrations.

We estimate the amount of $^{37}$Ar produced in natural xenon via cosmic ray-induced spallation, an inevitable consequence of the transportation and storage of xenon on the Earth's surface. We then calculate the resulting $^{37}$Ar concentration in a 10-tonne payload~(similar to that of the LUX-ZEPLIN experiment) assuming a representative schedule of xenon purification, storage and delivery to the underground facility. Using the spallation model by Silberberg and Tsao, the sea level production rate of $^{37}$Ar in natural xenon is estimated to be 0.024~atoms/kg/day. Assuming the xenon is successively purified to remove radioactive contaminants in 1-tonne batches at a rate of 1~tonne/month, the average $^{37}$Ar activity after 10~tonnes are purified and transported underground is 0.058--0.090~$\mu$Bq/kg, depending on the degree of argon removal during above-ground purification. Such cosmogenic $^{37}$Ar will appear as a noticeable background in the early science data, while decaying with a 35~day half-life. This newly-noticed production mechanism of $^{37}$Ar should be considered when planning for future liquid xenon-based experiments.

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.

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.

Two-phase xenon detectors, such as that at the core of the forthcoming LZ dark matter experiment, use photomultiplier tubes to sense the primary (S1) and secondary (S2) scintillation signals resulting from particle interactions in their liquid xenon target. This paper describes a simulation study exploring two techniques to lower the energy threshold of LZ to gain sensitivity to low-mass dark matter and astrophysical neutrinos, which will be applicable to other liquid xenon detectors. The energy threshold is determined by the number of detected S1 photons; typically, these must be recorded in three or more photomultiplier channels to avoid dark count coincidences that mimic real signals. To lower this threshold: a) we take advantage of the double photoelectron emission effect, whereby a single vacuum ultraviolet photon has a $\sim20\%$ probability of ejecting two photoelectrons from a photomultiplier tube photocathode; and b) we drop the requirement of an S1 signal altogether, and use only the ionization signal, which can be detected more efficiently. For both techniques we develop signal and background models for the nominal exposure, and explore accompanying systematic effects, including the dependence on the free electron lifetime in the liquid xenon. When incorporating double photoelectron signals, we predict a factor of $\sim 4$ sensitivity improvement to the dark matter-nucleon scattering cross-section at $2.5$ GeV/c$^2$, and a factor of $\sim1.6$ increase in the solar $^8$B neutrino detection rate. Dropping the S1 requirement may allow sensitivity gains of two orders of magnitude in both cases. Finally, we apply these techniques to even lower masses by taking into account the atomic Migdal effect; this could lower the dark matter particle mass threshold to $80$ MeV/c$^2$.

Author(s): LUX-ZEPLIN, The; Collaboration; Akerib, DS; Musalhi, AK Al; Alsum, SK; Amarasinghe, CS; Ames, A; Anderson, TJ; Angelides, N; Araujo, HM; Armstrong, JE; Arthurs, M; Bai, X; Balajthy, J; Balashov, S; Bang, J; Bargemann, JW; Bauer, D; Baxter, A; Beltrame, P; Bernard, EP; Bernstein, A; Bhatti, A; Biekert, A; Biesiadzinski, TP; Birch, HJ; Blockinger, GM; Boxer, B; Brew, CAJ; Bras, P; Burdin, S; Busenitz, JK; Buuck, M; Cabrita, R; Carmona-Benitez, MC; Cascella, M; Chan, C; Chott, NI; Cole, A; Converse, MV; Cottle, A; Cox, G; Creaner, O; Cutter, JE; Dahl, CE; Viveiros, L de; Dobson, JEY; Druszkiewicz, E; Eriksen, SR; Fan, A; Fayer, S; Fearon, NM; Fiorucci, S; Flaecher, H; Fraser, ED; Fruth, T; Gaitskell, RJ; Genovesi, J; Ghag, C; Gibson, E; Gokhale, S; Grinten, MGD van der; Gwilliam, CB; Hall, CR; Hardy, CA; Haselschwardt, SJ; Hertel, SA; Horn, M; Huang, DQ; Ignarra, CM; Jahangir, O; James, RS; Ji, W; Johnson, J; Kaboth, AC; Kamaha, AC; Kamdin, K; Kazkaz, K; Khaitan, D; Khazov, A; Khurana, I; Kodroff, D; Korley, L; Korolkova, EV; Kraus, H | Abstract: The projected sensitivity of the LUX-ZEPLIN (LZ) experiment to two-neutrino and neutrinoless double beta decay of $^{134}$Xe is presented. LZ is a 10-tonne xenon time projection chamber optimized for the detection of dark matter particles, that 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 beta 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$\times$10$^{24}$ years at 90% confidence level (CL), and has a three-sigma observation potential of 8.7$\times$10$^{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$\times$10$^{24}$ years at 90% CL.

LUX-ZEPLIN (LZ) is a dark matter detector expected to obtain world-leading sensitivity to weakly interacting massive particles (WIMPs) interacting via nuclear recoils with a ~7-tonne xenon target mass. This manuscript presents sensitivity projections to several low-energy signals of the complementary electron recoil signal type: 1) an effective neutrino magnetic moment and 2) an effective neutrino millicharge, both for pp-chain solar neutrinos, 3) an axion flux generated by the Sun, 4) axion-like particles forming the galactic dark matter, 5) hidden photons, 6) mirror dark matter, and 7) leptophilic dark matter. World-leading sensitivities are expected in each case, a result of the large 5.6t 1000d exposure and low expected rate of electron recoil backgrounds in the <100keV energy regime. A consistent signal generation, background model and profile-likelihood analysis framework is used throughout.

The Large Underground Xenon (LUX) dark matter search was a 250-kg active mass dual-phase time projection chamber that operated by detecting light and ionization signals from particles incident on a xenon target. In December 2015, LUX reported a minimum 90% upper C.L. of 6e-46 cm^2 on the spin-independent WIMP-nucleon elastic scattering cross section based on a 1.4e4 kg*day exposure in its first science run. Tension between experiments and the absence of a definitive positive detection suggest it would be prudent to search for WIMPs outside the standard spin-independent/spin-dependent paradigm. Recent theoretical work has identified a complete basis of 14 independent effective field theory (EFT) operators to describe WIMP-nucleon interactions. In addition to spin-independent and spin-dependent nuclear responses, these operators can produce novel responses such as angular-momentum-dependent and spin-orbit couplings. Here we report on a search for all 14 of these EFT couplings with data from LUX's first science run. Limits are placed on each coupling as a function of WIMP mass.

Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from gamma-rays emitted by K-40 and the U-238 and Th-232 decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4850-foot level. In order to characterise the cavern background, in-situ gamma-ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0-3300 keV) varied from 596 Hz to 1355 Hz for unshielded measurements, corresponding to a total flux from the cavern walls of 1.9 +/- 0.4 gamma cm(-2) s(-1). The resulting activity in the walls of the cavern can be characterised as 220 +/- 60 Bq/kg of K-40, 29 +/- 15 Bq/kg of U-238, and 13 +/- 3 Bq/kg of Th-232. (C) 2019 Elsevier B.V. All rights reserved.

The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double beta decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to 136 Xe neutrinoless double beta decay, taking advantage of the significant ( > 600 kg) 136 Xe mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of 136 Xe is projected to be 1.06 × 10 26 years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with 136 Xe at 1.06 × 10 27 years.

Author(s): Akerib, DS; Akerlof, CW; Alqahtani, A; Alsum, SK; Anderson, TJ; Angelides, N; Araujo, HM; Armstrong, JE; Arthurs, M; Bai, X; Balajthy, J; Balashov, S; Bang, J; Baxter, A; Bensinger, J; Bernard, EP; Bernstein, A; Bhatti, A; Biekert, A; Biesiadzinski, TP; Birch, HJ; Boast, KE; Boxer, B; Bras, P; Buckley, JH; Bugaev, VV; Burdin, S; Busenitz, JK; Cabrita, R; Carels, C; Carlsmith, DL; Benitez, MC Carmona; Cascella, M; Chan, C; Chott, NI; Cole, A; Cottle, A; Cutter, JE; Dahl, CE; Viveiros, L de; Dobson, JEY; Druszkiewicz, E; Edberg, TK; Eriksen, SR; Fan, A; Fiorucci, S; Flaecher, H; Fraser, ED; Fruth, T; Gaitskell, RJ; Genovesi, J; Ghag, C; Gibson, E; Gilchriese, MGD; Gokhale, S; Grinten, MGD van der; Hall, CR; Harrison, A; Haselschwardt, SJ; Hertel, SA; Hor, JYK; Horn, M; Huang, DQ; Ignarra, CM; Jahangir, O; Ji, W; Johnson, J; Kaboth, AC; Kamaha, AC; Kamdin, K; Kazkaz, K; Khaitan, D; Khazov, A; Khurana, I; Kocher, CD; Korley, L; Korolkova, EV; Kras, J; Kraus, H; Kravitz, S; Kreczko, L; Krikler, B; Kudryavtsev, VA; Leason, EA; Lee, J | Abstract: The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double beta decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to $^{136}$Xe neutrinoless double beta decay, taking advantage of the significant ($g$600 kg) $^{136}$Xe mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of $^{136}$Xe is projected to be 1.06$\times$10$^{26}$ years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with $^{136}$Xe at 1.06$\times$10$^{27}$ years.

LUX-ZEPLIN (LZ) is a next-generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with weakly interacting massive particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6-tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above 1.4 x 10(-48) cm(2) for a 40 GeV/c(2) mass WIMP. Additionally, a 5 sigma discovery potential is projected, reaching cross sections below the exclusion limits of recent experiments. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of 2.3 x 10(-43) cm(2) (7.1 x 10(-42) cm(2)) for a 40 GeV/c(2) mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020.

We describe the design and assembly of the LUX-ZEPLIN experiment, a direct detection search for cosmic WIMP dark matter particles. The centerpiece of the experiment is a large liquid xenon time projection chamber sensitive to low energy nuclear recoils. Rejection of backgrounds is enhanced by a Xe skin veto detector and by a liquid scintillator Outer Detector loaded with gadolinium for efficient neutron capture and tagging. LZ is located in the Davis Cavern at the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota, USA. We describe the major subsystems of the experiment and its key design features and requirements.