A recent discovery of additional mechanism of electroluminescence (EL) in noble gases due to the neutral bremsstrahlung (NBrS) effect led to a prediction that NBrS EL should be present in noble liquids as well. A theoretical model of NBrS EL in noble liquids was developed accordingly in the frameworks of Cohen-Lekner and Atrazhev. In this work, we confirm this prediction: for the first time, visible-range EL has been observed in liquid argon at electric fields reaching 90~kV/cm, using Gas Electron Multiplier (GEM) and Thick GEM (THGEM) structures. Absolute light yields of the EL were measured and found to be in excellent agreement with the theory, provided that the momentum-transfer cross section of electron scattering is used for calculation of NBrS cross section (instead of the energy-transfer one).
We further study the effect of neutral bremsstrahlung (NBrS) in two-phase argon electroluminescence (EL), revealed recently in [1]. The absolute EL yield due to NBrS effect, in the visible and NIR range, was remeasured in pure gaseous argon in the two-phase mode, using a two-phase detector with EL gap read out directly by cryogenic PMTs and SiPMs. Possible applications of the NBrS effect in detection science are discussed, including those in two-phase dark matter detectors.
The study of proportional electroluminescence in two-phase argon is relevant in the field of noble-gas liquid detectors for dark matter search and low-energy neutrino experiments. In this work, we continued to study proportional electroluminescence (EL) in two-phase argon doped with a minor (9 ppm) admixture of nitrogen, in the VUV, UV and visible spectral ranges. We confirmed the effect of enhancement of the EL yield, as well as the presence of non-VUV component in addition to that of VUV, in proportional electroluminescence in two-phase Ar. On the other hand, the contribution of non-VUV comp…
Proportional electroluminescence (EL) in noble gases has long been used in two-phase detectors for dark matter search, to record ionization signals induced by particle scattering in the noble-gas liquid (S2 signals). Until recently, it was believed that proportional electroluminescence was fully due to VUV emission of noble gas excimers produced in atomic collisions with excited atoms, the latter being in turn produced by drifting electrons. In this work we consider an additional mechanism of proportional electroluminescence, namely that of bremsstrahlung of drifting electrons scattered on neu…
Proportional electroluminescence (EL) is the physical effect used in two-phase detectors for dark matter searches, to optically record (in the gas phase) the ionization signal produced by particle scattering in the liquid phase. In our previous work the presence of a new EL mechanism, namely that of neutral bremsstrahlung (NBrS), was demonstrated in two-phase argon detectors both theoretically and experimentally, in addition to the ordinary EL mechanism due to excimer emission. In this work the similar theoretical approach is applied to all noble gases, i.e. overall to helium, neon, argon, kry…
Proportional electroluminescence (EL) is the physical effect used in two-phase dark matter detectors, to optically record in the gas phase the ionization signal produced by particle scattering in the liquid phase. In our previous works the presence of a new EL mechanism in noble gases, namely that of neutral bremsstrahlung (NBrS), was demonstrated both theoretically and experimentally, in addition to the ordinary EL mechanism due to excimer emission. In this work we show that the similar theoretical approach can apply to noble liquids, namely to liquid helium, neon, argon, krypton and xenon. I…
Gas Electroluminescence in a Dual Phase Xenon-Doped Argon Detector
Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；University of California Davis（加州大学戴维斯分校）；University of California San Diego（加州大学圣地亚哥分校）；University of California Riverside（加州大学河滨分校）
Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter search to record ionization signals in the gas phase induced by particle scattering in the liquid phase (S2 signals). In this work, the EL pulse-shapes in a two-phase argon detector have for the first time been studied systematically in a wide range of reduced electric field, varying from 3 to 9 Td. The pulse-shapes were studied at different readout configurations and spectral ranges: using cryogenic PMTs and SiPMs, with and without a wavelength shifter (WLS), in the VUV and visible range. We ob…
A measurement of ionization yields in noble-gas liquids is relevant to the energy calibration of nuclear recoil detectors for dark matter search and coherent neutrino-nucleus scattering experiments. In this work we further study the ionization yield of nuclear recoils in liquid Ar, using a two-phase detector with an electroluminescence gap and DD neutron generator. The ionization yields of nuclear recoils in liquid Ar were measured at 233 keV and electric fields of 0.56 and 0.62 kV/cm; their values amounted to 5.9 $\pm$ 0.8 and 7.4 $\pm$ 1 e$^-$/keV, respectively. The characteristic dependence…
Spectroscopic study of argon electroluminescence light with a wavelength-sensitive particle detector
Department of Physics, University of California, Davis（加州大学戴维斯分校物理系）；CIEMAT, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas（能源、环境和技术研究研究中心）
Proportional electroluminescence (EL) in noble gases is a physical process routinely used in two-phase (liquid-gas) detectors for low-energy astroparticle-physics experiments. In this work, the time properties of visible-light EL in two-phase argon detectors have been systematically studied for the first time. In particular, two unusual slow components in the EL signal, with their contributions and time constants increasing with electric field, were observed. This puzzling property is not expected in any of the known mechanisms of photon and electron emission in two-phase media. Time constants…
A two-phase Cryogenic Avalanche Detector (CRAD) with electroluminescence (EL) gap, operated in argon doped with a minor (49$\pm$7 ppm) admixture of nitrogen, has been studied. The EL gap was optically read out using cryogenic PMTs located on the perimeter of the gap. We present the results of the measurements of the N$_2$ content, detector sensitivity to X-ray-induced signals, EL gap yield and electron lifetime in the liquid. The detector sensitivity, at a drift field in liquid Ar of 0.6 kV/cm, was measured to be 9 and 16 photoelectrons recorded at the PMTs per keV of deposited energy at 23 an…
A double-phase Ar detector can efficiently identify particles and reconstruct their positions. However, the properties of electroluminescence (EL) for secondary light emission in the gas phase are not fully understood. Earlier studies have explained the EL process using an ordinary EL mechanism because of an Ar excimer; however, this mechanism does not predict the emission of visible light (VL). Recent measurements have demonstrated VL components in Ar gas EL, to explain which a new mechanism called neutral bremsstrahlung (NBrS) was proposed. In this study, we investigated gaseous Ar EL in the…
Electroluminescence and electron avalanching are the physical effects used in two-phase argon and xenon detectors for dark mater search and neutrino detection, to amplify the primary ionization signal directly in cryogenic noble-gas media. We review the concepts of such light and charge signal amplification, including a combination thereof, both in the gas and in the liquid phase. Puzzling aspects of the physics of electroluminescence and electron avalanching in two-phase detectors are explained and detection techniques based on these effects are described.
Proportional electroluminescence (EL) in gaseous Ar has for the first time been systematically studied in the two-phase mode, at 87 K and 1.00 atm. Liquid argon had a minor (56 ppm) admixture of nitrogen, which allowed to understand, inter alia, the effect of N2 doping on the EL mechanism in rare-event experiments using two-phase Ar detectors. The measurements were performed in a two-phase Cryogenic Avalanche Detector (CRAD) with EL gap located directly above the liquid-gas interface. The EL gap was optically read out in the Vacuum Ultraviolet (VUV), near 128 nm (Ar excimer emission), and in t…
We present the results of the operation of an array of avalanche photodiodes (APDs) for the readout of an electroluminescence detector. The detector contains 24 APDs with a pitch of 15 mm between them allowing energy and position measurements simultaneously. Measurements were performed in xenon (3.8 bar) and argon (4.8 bar) showing a good energy resolution of 5.3% FWHM at 60 keV in xenon and 9.4% in argon respectively. Following Monte Carlo studies the performance could be improved significantly by reducing the pitch between the sensors.
We demonstrate, for the time, the operation of a bubble-assisted Liquid Hole Multiplier (LHM) in liquid argon. The LHM, sensitive to both radiation-induced ionization electrons and primary scintillation photons, consists of a perforated electrode immersed in the noble liquid, with a stable gas-bubble trapped underneath. Electrons deposited in the liquid or scintillation-induced photoelectrons emitted from a photocathode on the electrode's surface, are collected into the holes; after crossing the liquid-gas interface, they induce electroluminescence within the bubble. After having validated in …
Traditionally, it has been assumed that electroluminescence (EL) in time projection chambers was purely an excimer-based emission. This idea changed when neutral bremsstrahlung (NBrS) was observed first in argon and subsequently in xenon a few years ago. In this work we explore further the framework used to explain these observations, presenting results for noble gas -based mixtures, as well as mixtures including small fractions of a molecular additive (`quencher'). Spectral content and yields are discussed in some cases of contemporary interest, together with their pressure-scalings.
As noble liquid time projection chambers grow in size their high voltage requirements increase, and detailed, reproducible studies of dielectric breakdown and the onset of electroluminescence are needed to inform their design. The Xenon Breakdown Apparatus (XeBrA) is a 5-liter cryogenic chamber built to characterize the DC high voltage breakdown behavior of liquid xenon and liquid argon. Electrodes with areas up to 33~cm$^2$ were tested while varying the cathode-anode separation from 1 to 6~mm with a voltage difference up to 75~kV. A power-law relationship between breakdown field and electrode…
We present a measurement of scintillation efficiency for a few tens of keV nuclear recoils (NR) with a liquid argon time projection chamber under electric fields ranging from $0$ to $3\ {\rm kV/cm}$. The calibration data are taken with $^{252}{\rm Cf}$ radioactive source. Observed scintillation and electroluminescence spectra are simultaneously fit with spectra derived from Geant4-based Monte Carlo simulation and an NR model. The scintillation efficiency extracted from the fit is reported as a function of recoil energy and electric field. This result can be used for designing the detector and …
The Deep Underground Neutrino Experiment (DUNE) is a leading-edge experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE-Dual Phase (DP) is a 6x6x6 m$^3$ liquid argon time-projection-chamber (LArTPC) operated at the CERN Neutrino Platform in 2019-2020 as a prototype of the DUNE Far Detector. In ProtoDUNE-DP, the scintillation and electroluminescence light produced by cosmic muons in the LArTPC is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. In this paper, we present the performance of the Proto…
A methodology to measure Near Infrared (NIR) scintillations in gaseous and liquid Ar, using Geiger-mode APDs (GAPDs) sensitive in the NIR and pulsed X-ray irradiation, is described. This study has been triggered by the development of Cryogenic Avalanche Detectors (CRADs) with optical readout in the NIR using combined THGEM/GAPD multiplier, which may come to be in demand in coherent neutrino-nucleus scattering and dark matter search experiments. A new approach to measure the NIR scintillation yield at cryogenic temperatures has been developed, namely using GAPDs in single photoelectron counting…
Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The "standard" EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms ("neutral bremsstrahlung", NBrS). The second, responsible for electron avalanche sci…
We report the measurement of the longitudinal diffusion constant in liquid argon with the DarkSide-50 dual-phase time projection chamber. The measurement is performed at drift electric fields of 100 V/cm, 150 V/cm, and 200 V/cm using high statistics $^{39}$Ar decays from atmospheric argon. We derive an expression to describe the pulse shape of the electroluminescence signal (S2) in dual-phase TPCs. The derived S2 pulse shape is fit to events from the uppermost portion of the TPC in order to characterize the radial dependence of the signal. The results are provided as inputs to the measurement …
The study of primary and secondary scintillations in noble gases and liquids is of paramount importance to rare-event experiments using noble gas media. In the present work, the scintillation yield in gaseous and liquid Ar has for the first time been measured in the near infrared (NIR) and visible region, both for primary and secondary (proportional) scintillations, using Geiger-mode avalanche photodiodes (G-APDs) and pulsed X-ray irradiation. The primary scintillation yield of the fast component was measured to be 17000 photon/MeV in gaseous Ar in the NIR, in the range of 690-1000 nm, and 510…
Liquid argon detectors are employed in a wide variety of nuclear and particle physics experiments. The addition of small quantities of xenon to argon modifies its scintillation, ionization, and electroluminescence properties and can improve its performance as a detection medium. However, a liquid argon-xenon mixture can develop instabilities, especially in systems that require phase transitions or that utilize high xenon concentrations. In this work, we discuss the causes for such instabilities and describe a small (liter-scale) apparatus with a unique cryogenic circuit specifically designed t…
We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White TPC and a dedicated setup. Detailed comparison with first-principle calculations allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that has been postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about 10$^{-2}$ photon/e$^{-}$ cm$^{-1}$ bar$^{-1}$ at pressure-reduced electric field values of 50 V cm$^{-1}$ bar$^{-1}$ to above 3$\times$10$^{-1}$ photon/e$^{-}$ …
We present here a comprehensive study of the light yield of primary and secondary scintillations produced in gaseous and liquid Ar in the near infrared (NIR) and visible region, at cryogenic temperatures. The measurements were performed using Geiger-mode avalanche photodiodes (GAPDs) and pulsed X-ray irradiation. The primary scintillation yield of the fast emission component in gaseous Ar was found to be independent of temperature in the range of 87-160 K; it amounted to 17000+/-3000 photon/MeV in the NIR in the range of 690-1000 nm. In liquid Ar at 87 K, the primary scintillation yield of the…
DarkSide-50 has demonstrated the high potential of dual-phase liquid argon time projection chambers in exploring interactions of WIMPs in the GeV/c$^2$ mass range. The technique, based on the detection of the ionization signal amplified via electroluminescence in the gas phase, allows to explore recoil energies down to the sub-keV range. We report here on the DarkSide-50 measurement of the ionization yield of electronic recoils down to $\sim$180~eV$_{er}$, exploiting $^{37}$Ar and $^{39}$Ar decays, and extrapolated to a few ionization electrons with the Thomas-Imel box model. Moreover, we pres…
A 10 kilo-tonne dual-phase liquid argon TPC is one of the detector options considered for the Deep Underground Neutrino Experiment (DUNE). The detector technology relies on amplification of the ionisation charge in ultra-pure argon vapour and oers several advantages compared to the traditional single-phase liquid argon TPCs. A 4.2 tonne dual-phase liquid argon TPC prototype, the largest of its kind, with an active volume of 3x1x1 $m^3$ has been constructed and operated at CERN. In this paper we describe in detail the experimental setup and detector components as well as report on the operation…
The $3 \times 1 \times 1$ m$^3$ demonstrator is a dual phase liquid argon time projection chamber that has recorded cosmic rays events in 2017 at CERN. The light signal in these detectors is crucial to provide precise timing capabilities. The performances of the photon detection system, composed of five PMTs, are discussed. The collected scintillation and electroluminescence light created by passing particles has been studied in various detector conditions. In particular, the scintillation light production and propagation processes have been analyzed and compared to simulations, improving the …
DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE Dual Phase (DP) is a 6x6x6m3 liquid argon time-projection-chamber (LArTPC) that recorded cosmic-muon data at the CERN Neutrino Platform in 2019-2020 as a prototype of the DUNE Far Detector. Charged particles propagating through the LArTPC produce ionization and scintillation light. The scintillation light signal in these detectors can provide the trigger for non-beam events. In addition, it adds precise timing capabilities and improves the calorimetry measu…
