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Register a new userIncreasing the efficiency of photon collection in LArTPCs: the ARAPUCA light trap
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The Liquid Argon Time Projection Chambers (LArTPCs) are a choice for the next generation of large neutrino detectors due to their optimal performance in particle tracking and calorimetry. The detection of Argon scintillation light plays a crucial role in the event reconstruction as well as the time reference for non-beam physics such as supernovae neutrino detection and baryon number violation studies. In this contribution, we present the current R&D work on the ARAPUCA (Argon R&D Advanced Program at UNICAMP), a light trap device to enhance Ar scintillation light collection and thus the overall performance of LArTPCs. The ARAPUCA working principle is based on a suitable combination of dichroic filters and wavelength shifters to achieve a high efficiency in light collection. We discuss the operational principles, the last results of laboratory tests and the application of the ARAPUCA as the alternative photon detection system in the protoDUNE detector.
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In the Fall of 2017, two photon detector designs for the Deep Underground Neutrino Experiment (DUNE) Far Detector were installed and tested in the TallBo liquid argon (LAr) cryostat at the Proton Assembly (PAB) facility, Fermilab. The designs include two light bars developed at Indiana University and a photon detector based on the ARAPUCA light trap engineered by Colorado State University and Fermilab. The performance of these devices is determined by analyzing 8 weeks of cosmic ray data. The current paper focuses solely on the ARAPUCA device as the performance of the light bars will be reported separately. The paper briefly describes the ARAPUCA concept, the TallBo setup, and focuses on data analysis and results.
In the Deep Underground Neutrino Experiment (DUNE), the VUV LAr luminescence is collected by light trap devices named X-Arapuca, sizing (480x93) mm2. Six thousand of these units will be deployed in the first DUNE ten kiloton far detector module. In this work we present the first characterization of the photon detection efficiency of an X-Arapuca device sizing (200x75) mm2 via a complete and accurate set of measurements along the cell longitudinal axis with a movable 241-Am source. The MPPCs photosensors are readout by a cryogenic transimpedance amplifier to enhance the single photoelectron sensitivity and improve the signal-to-noise while ganging 8 MPPC for a total surface of 288 mm2. Moreover we developed a new photon downshifting polymeric material, by which the X-Arapuca photon detection efficiency was enhanced of about +50% with respect to the baseline off-shell product deployed in the standard device configuration. The achieved results are compared to previous measurements on a half size X-Arapuca device, with a fixed source facing the center, with no cold amplification stage, and discussed in view of the DUNE full size optical cell construction for both the horizontal and the vertical drift configurations of the DUNE TPC design and in view of liquid Argon doping by ppms of Xe. Other particle physics projects adopting Liquid Argon as target or active veto, as Dark Side and LEGEND or the DUNE Near Detector will take advantage of this novel wavelength shifting material.
Simulations of photon propagation in scintillation detectors were performed with the aim to find the optimal scintillator geometry, surface treatment, and shape of external reflector in order to achieve maximum light collection efficiency for detector configurations that avoid direct optical coupling, a situation that is commonly found in cryogenic scintillating bolometers in experimental searches for double beta decay and dark matter. To evaluate the light collection efficiency of various geometrical configurations we used the ZEMAX ray-tracing software. It was found that scintillators in the shape of a triangular prism with an external mirror shaped as truncated cone gives the highest light collection efficiency. The results of the simulations were confirmed by carrying out measurements of the light collection efficiencies of CaWO4 crystal scintillators. A comparison of simulated and measured values of light output shows good agreement
The ARAPUCA is a novel concept for liquid argon scintillation light detection which has been proposed for the photon detection system of the Deep Underground Neutrino Experiment. The test in liquid argon of one of the first ARAPUCA prototypes is presented in this work, where the working principle is experimentally demonstrated. The prototype has an acceptance window of 9 cm$^2$ and is read-out by a single SiPM with active area of 0.36 cm$^2$. Its global detection efficiency was estimated by exposing it to a $^{238}U$ $alpha$ source and to cosmic rays and was found to be 1.15% $pm$ 0.15%, in good agreement with the prediction of a detailed Monte Carlo simulation of the device. Several other ARAPUCA prototypes of bigger dimensions and read-out by arrays of SiPMs have been built and are actually under test. In particular 32 ARAPUCA cells have been installed inside the protoDUNE detector, which is being assembled at CERN and will be operated in the second half of 2018.
Low noise CCDs fully-depleted up to 675 micrometers have been identified as a unique tool for Dark Matter searches and low energy neutrino physics. The charge collection efficiency (CCE) for these detectors is a critical parameter for the performance of future experiments. We present here a new technique to characterize CCE in back-illuminated CCDs based on soft X-rays. This technique is used to characterize two different detector designs. The results demonstrate the importance of the backside processing for detection near threshold, showing that a recombination layer of a few microns significantly distorts the low energy spectrum. The studies demonstrate that the region of partial charge collection can be reduced to less than 1 micrometer thickness with adequate backside processing.
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