Light Readout System Research Articles

Improvement and Characterisation of the ArCLight Large-Area Dielectric Light Detector for Liquid-Argon Time Projection Chambers

The detection of scintillation light in noble-liquid detectors is necessary for identifying neutrino interaction candidates from beam, astrophysical, or solar sources. Large monolithic detectors typically have highly efficient light sensors, like photomultipliers, mounted outside their electric field. This option is not available for modular detectors that wish to maximize their active volume. The ArgonCube light readout system detectors (ArCLights) are large-area thin-wavelength-shifting (WLS) panels that can operate in highly proximate modular detectors and within the electric field. The WLS plastic forming the bulk structure of the ArCLight has Tetraphenyl Butadiene (TPB) and sheets of dichroic mirror layered across its surface. It is coupled to a set of six silicon photomultipliers (SiPMs). This publication compares TPB coating techniques for large surface areas and describes quality control methods for large-scale production.

The DarkSide-20k experiment

The DarkSide-20k experiment represents the present goal of the Global Argon Dark Matter Collaboration program. Bringing together the experience from previous argon-based detectors, as well as the knowledge gained on large volume membrane cryostats developed within the DUNE program, the community is now building a dual-phase LAr-TPC equipped with SiPM arrays for light readout. The main goal of the experiment is to discover or to extend the current sensitivity limits on the search for dark matter WIMP-like particles. Currently, the experiment has entered the construction phase and the external cryostat is being put in place at Laboratori Nazionali del Gran Sasso (LNGS), Italy. Detector construction will follow, and data taking is expected to start in late 2026. This contribution will introduce the DarkSide detector and goals, and it will report on the ongoing construction of the underground infrastructure at LNGS. Finally, it will concentrate on the current activities on large arrays of silicon light detectors, that are at the base of the construction of the detector light readout system.

Upgrade of the scintillator detector for particle tracking in experiments with antiprotons

Experiments with antiprotons often require the tracking of charged particles emerging from the annihilation process. The Atomic Spectroscopy And Collisions Using Slow Antiprotons (ASACUSA) collaboration at the CERN Antiproton Decelerator (AD) used several panels of scintillating bars placed around the interaction region to detect the passage of charged pions and determine the annihilation vertex position and time. The panels were composed by extruded scintillating bars and the light was collected using WaveLength Shifting (WLS) fibers and multi-anode PhotoMultiplier Tubes (PMTs). After operating for several years, the fiber-PMT coupling quality had degraded and a major upgrade of the light readout system was planned. The PMTs will be replaced by Silicon PhotoMultipliers (SiPMs) and the front-end electronics changed accordingly. An improvement is expected in the efficiency and the uniformity of the detector response. In this contribution the commissioning of the upgrade will be described, including the results of preliminary tests with cosmic rays.

Liquid argon light collection and veto modeling in GERDA Phase II

The ability to detect liquid argon scintillation light from within a densely packed high-purity germanium detector array allowed the Gerda experiment to reach an exceptionally low background rate in the search for neutrinoless double beta decay of {}^{76}Ge. Proper modeling of the light propagation throughout the experimental setup, from any origin in the liquid argon volume to its eventual detection by the novel light read-out system, provides insight into the rejection capability and is a necessary ingredient to obtain robust background predictions. In this paper, we present a model of the Gerda liquid argon veto, as obtained by Monte Carlo simulations and constrained by calibration data, and highlight its application for background decomposition.

A Tetramethylsilane TPC with Cherenkov light readout and 3D reconstruction

We describe the construction and calibration of a multi-channel liquid time projection chamber filled with Tetramethylsilane. Its charge readout system consists of 8 wires each in the X and Y directions. The chamber is also equipped with a light readout system consisting of a 5′′ photomultiplier tube coupled to the liquid volume through a viewport. The energy scale of the detector is calibrated using positron–electron pairs produced by 4.4 MeV gamma rays emitted from an AmBe source, using an external trigger on the positron annihilation gammas. The external trigger is then reconfigured to tag cosmic ray muons passing through the active Tetramethylsilane volume, which are used to measure the stopping power in Tetramethylsilane and the electron lifetime in the detector. We find a most-probable energy loss from minimum ionizing particles of Δp∕ds = (0.60 ± 0.01) MeV/cm. We also measure an electron lifetime of 43−21+680μs by measuring the most-probable energy loss as a function of drift time. For both measurements, the errors are statistical only. For both fast electron and muon signals, the photomultiplier tube detects prompt Cherenkov light, demonstrating the possibility of self-triggering of the detector. The room-temperature organic target medium, together with the self-triggering capabilities and long electron lifetimes reported in this work, make this an attractive technology to explore for rare event detectors or other applications in the area of radiation measurements.

A New Concept for Kilotonne Scale Liquid Argon Time Projection Chambers

We develop a novel Time Projection Chamber (TPC) concept suitable for deployment in kilotonne-scale detectors, with a charge-readout system free from reconstruction ambiguities, and a robust TPC design that reduces high-voltage risks while increasing the coverage of the light-collection system and maximizing the active volume. This novel concept could be used as a far detector module in the Deep Underground Neutrino Experiment (DUNE). For the charge-readout system, we used the charge-collection pixels and associated application-specific integrated circuits currently being developed for the liquid argon (LAr) component of the DUNE Near Detector design, ArgonCube. In addition, we divided the TPC into a number of shorter drift volumes, reducing the total voltage used to drift the ionization electrons, and minimizing the stored energy per TPC. Segmenting the TPC also contains scintillation light, allowing for precise trigger localization and a more expansive light-readout system. Furthermore, the design opens the possibility of replacing or upgrading components. These augmentations could substantially improve the reliability and the sensitivity, particularly for low-energy signals, in comparison to traditional monolithic LArTPCs with projective-wire charge readouts.

ArCLight—A Compact Dielectric Large-Area Photon Detector

ArgonCube Light readout system (ArCLight) is a novel device for detecting scintillation light over large areas with Photon Detection Efficiency (PDE) of the order of a few percent. Its robust technological design allows for efficient use in large-volume particle detectors, such as Liquid Argon Time Projection Chambers (LArTPCs) or liquid scintillator detectors. Due to its dielectric structure it can be placed inside volumes with high electric field. It could potentially replace vacuum PhotoMultiplier Tubes (PMTs) in applications where high PDE is not required. The photon detection efficiency for a 10 × 10 cm2 detector prototype was measured to be in the range of 0.8% to 2.2% across the active area.

Testbeam performance of a shashlik calorimeter with fine-grained longitudinal segmentation

An iron- plastic-scintillator shashlik calorimeter with a 4.3 X0 longitudinal segmentation was tested in November 2016 at the CERN East Area facility with charged particles up to 5 GeV . The performance of this detector in terms of electron energy resolution, linearity, response to muons and hadron showers are presented in this paper and compared with simulation. Such a fine-grained longitudinal segmentation is achieved using a very compact light readout system developed by the SCENTT and ENUBET Collaborations, which is based on fiber-SiPM coupling boards embedded in the bulk of the detector. We demonstrate that this system fulfills the requirements for neutrino physics applications and discuss performance and additional improvements.

A compact light readout system for longitudinally segmented shashlik calorimeters

The longitudinal segmentation of shashlik calorimeters is challenged by dead zones and non-uniformities introduced by the light collection and readout system. This limitation can be overcome by direct fiber–photosensor coupling, avoiding routing and bundling of the wavelength shifter fibers and embedding ultra-compact photosensors (SiPMs) in the bulk of the calorimeter. We present the first experimental test of this readout scheme performed at the CERN PS-T9 beamline in 2015 with negative particles in the 1–5GeV energy range. In this paper, we demonstrate that the scheme does not compromise the energy resolution and linearity compared with standard light collection and readout systems. In addition, we study the performance of the calorimeter for partially contained charged hadrons to assess the e/π separation capability and the response of the photosensors to direct ionization.

Light-based triggering and reconstruction of Michel electrons in LArIAT

The LArIAT Experiment aims to calibrate the liquid argon time projection chamber (LArTPC) using a beam of charged particles at the Fermilab Test Beam Facility. It is equipped with a novel scintillation light readout system using PMTs and custom SiPM preamplifier boards to detect light from reflector foils coated with wavelength-shifting TPB. A trigger on delayed secondary flashes of light captures events containing stopping cosmic muons together with the Michel electrons coming from their subsequent decay. This dedicated Michel trigger supplies an abundant sample of low-energy electrons throughout the detector's active volume, providing opportunities to study the combined calorimetric capabilities of the light system and the TPC. Preliminary results using scintillation light to study properties of the Michel electron sample are presented.

A light readout system for gas TPCs

A novel light detection scheme has been tested for use in medium-pressuregas TPCs, in view of rare events searches in low energy particle physics. It has the advantage of minimal interference with the ionization collectionsystem, used for track imaging. It provides an absolute time reference, which allows an absolute determination of the Z coordinate of events, along the direction of the drift field. This makes possible a fiducial cut along the Z-axis, allowing to reduce the background from the ends of the drift volume.

PD-0036 OPTIMIZED OUTPUT FACTOR MEASUREMENT METHOD FOR CYBERKNIFE COLLIMATORS

than 10 mm. Our approach is to develop a phantom that contains an embedded array of plastic scintillators coupled to square air core light guides. The prototype array allows for accurate verification of fields as small as 4 mm, with high spatial and temporal resolution and without the need for correction factors. Materials and Methods: The 16 element linear array was constructed from custom cut PMMA sheets. Plastic scintillation detectors (BC400) of volume 0.8 mm3 were placed in 1 x 1 mm silvered square air core waveguides to avoid the production of a Cerenkov background signal in the primary field. The 16 detector elements have a center-tocenter spacing of 2 mm and an edge-to-edge distance of 1 mm and provide high resolution profiles of small treatment fields and of high dose gradients.Scintillation light from the air core array was measured with a photomultiplier tube (PMT) array detector, enabling measurements with high temporal resolution (10 Hz). This scintillation light readout system and user interface software was optimized for clinical use.The array was placed in a water equivalent medium in order to measure the beam output factors, percentage depth dose and beam profiles of radiation fields produced by a Varian Novalis TX linac. The array was then displaced laterally three times for measuring the beam profile, increasing the array's spatial resolution to 0.5 mm. Results: The PMMA light guides of 1 mm square cross section and 180 mm length show 5 times more light transmission than the previously used circular light guides of 1 mm diameter of the same length. The dose measurements were compared to those measured using a single air core dosimeter and other commercially available dosimeters. This experimentally confirms the suitability of the air core array for small field dosimetry with no corrections needed for angular dependence or dose perturbation as currently required by commercial arrays.

High energy gamma-ray spectroscopy with LaBr 3 scintillation detectors

Lanthanum bromide scintillation detectors produce very high light outputs (∼60,000 ph/MeV) within a very short decay time (typically ∼20 ns) which means that high instantaneous currents can be generated in the photocathode and dynode chain of the photomultiplier tube (PMT) used for the scintillation readout. The net result is that signal saturation can occur long before the recommended PMT biasing conditions can be reached. In search of an optimized light readout system for LaBr 3, we have tested and compared two different PMT configurations for detection of gamma-rays up to 15 MeV. This range was chosen as being appropriate for gamma-ray remote sensing and medium energy nuclear physics applications. The experiments were conducted at two facilities: the Laboratori Nazionali del Sud (LNS) in Catania, Italy [1] and the High Intensity Gamma-ray Source (HIγS) at Triangle University Nuclear Laboratory, in Durham, North Carolina, USA [2]. The PMT configurations we have tested are (1) a standard dynode chain operated under-biased; (2) a 4-stage reduced chain operated at nominal inter-dynode bias. The results are that shortening the number of active stages, as in configuration (2), has advantages in preserving energy resolution and avoiding PMT saturation over a large energy range. However, the use of an under-biased PMT, configuration (1), can still be considered a satisfactory solution, at least in the case of PMTs manufactured by Photonis. The results of this study will be used in support of the Mercury Gamma-ray and Neutron Spectrometer (MGNS) on board of BepiColombo, the joint ESA/JAXA mission to Mercury, scheduled for launch in 2014.

The argon dark matter experiment (ArDM)

The ArDM experiment, a 1ton liquid argon TPC/Calorimeter, is designed for the detection of dark matter particles which can scatter off the spinless argon nucleus, producing nuclear recoils. These events will be discerned by their light to charge ratio, as well as the time structure of the scintillation light. The experiment is presently under construction and commissioning on surface at CERN. Cryogenic operation and light detection performance was recently confirmed in a test run of the full 1ton liquid argon target under purely calorimetric operation and with a prototype light readout system. This note describes the experimental concept, the main detector components and presents some first results.

The ArDM project: A liquid argon TPC for dark matter detection

ArDM is a new-generation WIMP detector which will measure simultaneously light and charge from scintillation and ionization of liquid argon. Our goal is to construct, characterize and operate a 1 ton liquid argon underground detector. The project relies on the possibility to extract the electrons produced by ionization from the liquid into the gas phase of the detector, to amplify and read out with Large Electron Multipliers detectors. Argon VUV scintillation light has to be converted with wavelength shifters such as TetraPhenyl Butadiene in order to be detected by photomultipliers with bialkali photocathodes. We describe the status of the LEM based charge readout and light readout system R&D and the first light readout tests with warm and cold argon gas in the full size detector.

A new light readout system for the LXeGRIT time projection chamber

LXeGRIT is a liquid xenon time projection chamber (LXeTPC) used as balloon-borne Compton telescope for imaging cosmic sources in the MeV energy band. The three-dimensional position sensitive charge readout is triggered by the xenon scintillation light. In the original chamber design, the light is detected by four UV sensitive, 2'' PMT's (EMI 9813), coupled to the liquid xenon vessel by quartz windows. In order to improve the trigger efficiency and uniformity, a new light readout system has been studied. It consists of 12 UV sensitive, compact 2'' PMT's (Hamamatsu R6041Q), mounted in Teflon frames which cover the four sides of the LXeTPC active volume. These all-metal PMT's were especially developed to work at liquid xenon temperature and up to 3.5 atm overpressure. Light simulations promise an increase in light collection efficiency by more than a factor of ten for the new readout. We present simulations of the light collection efficiency and initial results from the successful operation of the new PMT fully immersed in liquid xenon.