Large Liquid Argon Detectors Research Articles

Can strangelets be detected in a large LAr neutrino detector?

Predicted as possible bound states of up, down and strange quarks, strangelets could be more energetically favourable and more stable than nuclear matter. In this paper we explore the possibility of detecting such particles with the future large liquid argon detectors developed for neutrino physics. Using signals from ionization and scintillation, as well as measuring the range, we suggest that a calorimetric TPC detector is able to put in evidence and to discriminate between light strangelets and normal isotopes at intermediate energies.

Modeling impurity concentrations in liquid argon detectors

Impurities in noble liquid detectors used for neutrino and dark matter experiments can significantly impact the quality of data. We present an experimentally verified model for describing the dynamics of impurity distributions in liquid argon (LAr) detectors. The model considers sources, sinks, and transport of impurities within and between the gas and liquid argon phases. Measurements of oxygen concentrations in a 20-L LAr multi-purpose test stand are compared to calculations made with this model to show that an accurate description of the concentrations under various operational conditions can be obtained. A result of this analysis is a determination of Henry’s coefficient for oxygen in LAr. These calculations also show that some processes have small effects on the impurity dynamics and excluding them yields a solution as a sum of two exponential terms. This solution provides a simple way to extract Henry’s coefficient with negligible approximation error. It is applied to the data and the Henry’s coefficient for oxygen in LAr is obtained as 0.84−0.05+0.09, consistent with literature results. Based on the analysis of the data with the model, we further suggest that, for a large liquid argon detector, barriers to flow (“baffles”) installed in the gas phase to restrict flow can help reduce the ultimate impurity concentration in the LAr.

Design and construction of a new detector to measure ultra-low radioactive-isotope contamination of argon

Large liquid argon detectors offer one of the best avenues for the detection of galactic weakly interacting massive particles (WIMPs) via their scattering on atomic nuclei. The liquid argon target allows exquisite discrimination between nuclear and electron recoil signals via pulse-shape discrimination of the scintillation signals. Atmospheric argon (AAr), however, has a naturally occurring radioactive isotope, 39Ar, a β emitter of cosmogenic origin. For large detectors, the atmospheric 39Ar activity poses pile-up concerns. The use of argon extracted from underground wells, deprived of 39Ar, is key to the physics potential of these experiments. The DarkSide-20k dark matter search experiment will operate a dual-phase time projection chamber with 50 tonnes of radio-pure underground argon (UAr), that was shown to be depleted of 39Ar with respect to AAr by a factor larger than 1400. Assessing the 39Ar content of the UAr during extraction is crucial for the success of DarkSide-20k, as well as for future experiments of the Global Argon Dark Matter Collaboration (GADMC). This will be carried out by the DArT in ArDM experiment, a small chamber made with extremely radio-pure materials that will be placed at the centre of the ArDM detector, in the Canfranc Underground Laboratory (LSC) in Spain. The ArDM LAr volume acts as an active veto for background radioactivity, mostly γ-rays from the ArDM detector materials and the surrounding rock. This article describes the DArT in ArDM project, including the chamber design and construction, and reviews the background required to achieve the expected performance of the detector.

A novel use of light guides and wavelength shifting plates for the detection of scintillation photons in large liquid argon detectors

Scintillation light generated as charged particles traverse large liquid argon detectors adds valuable information to studies of weakly-interacting particles. This paper uses both laboratory measurements and cosmic ray data from the Blanche dewar facility at Fermilab to characterize the efficiency of the photon detector technology developed at Indiana University for the single phase far detector of DUNE. The efficiency of this technology was found to be 0.48% at the readout end when the detector components were characterized with laboratory measurements. A second determination of the efficiency using cosmic ray tracks is in reasonable agreement with the laboratory determination. The agreement of these two efficiency determinations supports the result that minimum ionizing muons generate Nphot=40,000 photons/MeV as they cross the LAr volume.

The ProtoDUNE large demonstrator of the Liquid Argon double phase TPC program at CERN

The Deep Underground Neutrino Experiment (DUNE) will use a large liquid argon detector consisting of four modules each with a fiducial mass of 10 kt. A liquid-argon TPC working in double phase mode has been proposed as one of the first modules. The protoDUNE DP is a large demonstrator of the double phase liquid argon TPC with a 6×6×6 m3 (300t) active volume. ProtoDUNE DP is under construction at CERN and will be exposed to a charged particle beam (0.5-20 GeV/c) in 2018.

Index of refraction, Rayleigh scattering length, and Sellmeier coefficients in solid and liquid argon and xenon

Large liquid argon detectors have become widely used in low rate experiments, including dark matter and neutrino research. However, the optical properties of liquid argon are not well understood at the large scales relevant for current and near-future detectors. The index of refraction of liquid argon at the scintillation wavelength has not been measured, and current Rayleigh scattering length calculations disagree with measurements. Furthermore, the Rayleigh scattering length and index of refraction of solid argon and solid xenon at their scintillation wavelengths have not been previously measured or calculated. We introduce a new calculation using existing data in liquid and solid argon and xenon to extrapolate the optical properties at the scintillation wavelengths using the Sellmeier dispersion relationship.

Performance and Results of the LBNE 35 Ton Membrane Cryostat Prototype

We report on the performance and commissioning of the first membrane cryostat to be used for scientific application. The Long Baseline Neutrino Experiment (LBNE) has designed and fabricated a membrane cryostat prototype in collaboration with Ishikawajima-Harima Heavy Industries Co., Ltd. (IHI). LBNE has designed and fabricated the supporting cryogenic system infrastructure and successfully commissioned and operated the first membrane cryostat. Original goals of the prototype are: to demonstrate the membrane cryostat technology in terms of thermal performance, feasibility for liquid argon and leak tightness; to demonstrate that we can remove all the impurities from the vessel and achieve the purity requirements in a membrane cryostat without evacuation; to demonstrate that we can achieve and maintain the purity requirements of the liquid argon using mol sieve and copper filters. The purity requirements of a large liquid argon detector such as LBNE are contaminants below 200 parts per trillion (ppt) oxygen equivalent. LBNE is planning the design and construction of a large liquid argon detector. This presentation will present requirements, design and construction of the LBNE 35 ton membrane cryostat prototype, and detail the commissioning and performance. The experience and results of this prototype are extremely important for the development of the LBNE detector.

Expected performance of an ideal liquid argon neutrino detector with enhanced sensitivity to scintillation light

Scintillation light is used in liquid argon (LAr) neutrino detectors to provide a trigger signal, veto information against cosmic rays, and absolute event timing. In this work, we discuss additional opportunities offered by detectors with enhanced sensitivity to scintillation light, that is with light collection efficiencies of about 10-3. We focus on two key detector performance indicators for neutrino oscillation physics: calorimetric neutrino energy reconstruction and neutrino/antineutrino separation in a non-magnetized detector. Our results are based on detailed simulations, with neutrino interactions modelled according to the GENIE event generator, while the charge and light responses of a large LAr ideal detector are described by the Geant4 and NEST simulation tools. A neutrino energy resolution as good as 3.3% RMS for 4 GeV electron neutrino charged-current interactions can in principle be obtained in a large detector of this type, by using both charge and light information. By exploiting muon capture in argon and scintillation light information to veto muon decay electrons, we also obtain muon neutrino identification efficiencies of about 50%, and muon antineutrino misidentification rates at the few percent level, for few-GeV neutrino interactions that are fully contained. We argue that the construction of large LAr detectors with sufficiently high light collection efficiencies is in principle possible.

Beam-induced effects and radiological issues in high-intensity high-energy fixed target experiments

The next generation of accelerators for Megawatt beams moves us into a completely new domain of extreme specific energies of up to 0.1 MJ/g (Megajoule/gram) and specific power up to 1 TW/g (Terawatt/gram) in interactions with matter. The paper is focused on deleterious effects of controlled and uncontrolled impacts of such beams on components of beam-lines, target stations, beam absorbers, shielding and environment. Two new experiments at Fermilab are taken as an example. The Long-Baseline Neutrino Experiment (LBNE) will explore the interactions of the world's highest-intensity neutrino beam by sending it from Fermilab more than 1,000 kilometers through the Earth's mantle to a large liquid argon detector. The Mu2e experiment is devoted to studies of the conversion of a negative muon to electron in the field of a nucleus without emission of neutrinos.

Atmospheric neutrinos as a probe ofeV2-scale active-sterile oscillations

The downgoing atmospheric ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ fluxes can be significantly altered due to the presence of ${\mathrm{eV}}^{2}$-scale active-sterile oscillations. We study the sensitivity of a large liquid argon detector and a large magnetized iron detector (like the proposed ICAL at INO) to these oscillations. Such oscillations are indicated by results from LSND, and more recently, from MiniBooNE and from reanalyses of reactor experiments following recent recalculations of reactor fluxes. There are other tentative indications of the presence of sterile states in both the $\ensuremath{\nu}$ and $\overline{\ensuremath{\nu}}$ sectors as well. Using the allowed sterile parameter ranges in a $3+1$ mixing framework in order to test these results, we perform a fit assuming active-sterile oscillations in both the muon neutrino and antineutrino sectors, and compute oscillation exclusion limits using atmospheric downgoing muon neutrino and antineutrino events. We find that (for both ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$) a liquid argon detector, an ICAL-like detector or a combined analysis of both detectors with an exposure of $1\text{ }\text{ }\mathrm{Mt}/\mathrm{yr}$ provides significant sensitivity to regions of parameter space in the range $0.1<\ensuremath{\Delta}{m}^{2}<5\text{ }\text{ }{\mathrm{eV}}^{2}$ for ${sin}^{2}2{\ensuremath{\Theta}}_{\ensuremath{\mu}\ensuremath{\mu}}\ensuremath{\ge}0.08$. Thus atmospheric neutrino experiments can provide complementary coverage in these regions, improving sensitivity limits in combination with bounds from other experiments on these parameters. We also analyze the bounds using muon antineutrino events only and compare them with the results from MiniBooNE.

Light Readout Optimisation using Wavelength Shifter - Reflector Combinations

The use of reflectors coated with a wavelength shifter (WLS) along with standard bialkali PMTs is an economical method for an efficient readout system for vacuum ultra violet (VUV) light produced in large liquid argon detectors. Various thicknesses of tetraphenyl butadiene (TPB) were deposited by spraying and vacuum evaporation onto both specular 3MTM-foil and diffuse TetratexTM (TTX) reflectors. 128 nm VUV light generated in 1 bar argon gas by a 5.4 MeV α source was detected by a 3-inch bialkali borosilicate PMT within a 1 m tube lined internally with a TPB coated reflector. The light collection was recorded as a function of separation between source and PMT for each combination of coating and reflector for distances up to 1m. Reflection coefficients of TPB coated reflectors were measured using a spectroradiometer. WLS coating on the PMT window was also studied. The optimum coating and reflector combination was TPB evaporated on TTX. Measurements with coating thicknesses of 0.2 mg/cm2 and 1.0 mg/cm2 yielded a similar performance. The best PMT window coating is obtained by TPB evaporation of 0.05 mg/cm2.

Optical readout of liquid argon ionisation

Reading out the charge from a very large liquid argon detector, such as proposed for next generation proton decay and long baseline neutrino detectors, represents a significant challenge. Current proposals suggest using wires in the liquid or a two-phase approach that can provide some gain via amplification in the gas phase. We present here work on an alternative new approach in which the charge is read out by optical means following generation of electroluminescence, such as in a THGEM (Thick Gas Electron Multiplier) mounted within the liquid. This has the potential for significant advantages by providing both simpler readout electronics and significant charge gain, without the need for the complexities of dual phase operation. Tests with a silicon photomultiplier (SiPM) mounted above a THGEM, all submerged in liquid argon, have allowed first demonstration of the technique. Sensitivity to 5.9 keV 55Fe gamma events was observed with an estimated gain of 150 photoelectrons per drifted electron. We review the concepts and results.

Status of the ICARUS Experiment

The final phase of the ICARUS physics program requires a sensitive mass of liquid Argon of 5000 tons or more. This is still true today, even after the operation of large or the planning of even larger underground detectors. The superior bubble-chamber-like features of the ICARUS detector will always provide additional and fundamental contributions to the field. The most conservative way to reach a liquid Argon sensitive mass of 5000 tons is to start with a first prototype of a modest mass: the T600 detector. This step-wise strategy allowed to develop progressively the necessary know-how to build a large liquid Argon detector. After the successful completion of a series of technical tests to be performed at the assembly hall in Pavia, the T600 detector will be ready to be transported into the LNGS tunnel.