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1. A study of events with photoelectric emission in the DarkSide-50 liquid argon Time Projection Chamber

   The DarkSide-50 Collaboration) Agnes, P. ; Albuquerque, I. F. ; Alexander, T. ; Alton, A. K. ; Ave, M. ; Back, H. O. ; Batignani, G. ; Biery, K. ; Bocci, V. ; Bonivento, W. M. ; et al ( July 2021 , ArXivorg)

   null (Ed.)

   Finding unambiguous evidence of dark matter interactions in a particle detector is a main objective of physics research. The liquid argon time projection chamber technique for the detection of Weakly Interacting Massive Particles (WIMP) allows sensitivities down to the so-called neutrino floor for high and low WIMP masses. Based on the successful operation of the DarkSide-50 detector, a new and more sensitive experiment, DarkSide-20k, was designed and is now under construction. A thorough understanding of the DarkSide-50 detector response to events classified as dark matter as well as all other interactions is essential for an optimal design of the new experiment. In this paper, we report on a particular set of events, for which scintillation-ionization signals are observed in association with signals from single or few isolated electrons. We identified and provided an interpretation for two event types in which electrons are produced via photoelectric effect on the cathode electrode and in the bulk liquid. Events with photoelectric emissions are observed in association with most interactions with large energy depositions in the detector. From the measured rate of these events, we determine the photo-ionization probability, or photoelectric quantum efficiency, of tetraphenyl butadiene (TPB) at wavelengths around 128 nm. 

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2. Direct comparison of PEN and TPB wavelength shifters in a liquid argon detector

   https://doi.org/10.1140/epjc/s10052-021-09870-7  

   Boulay, M. G. ; Camillo, V. ; Canci, N. ; Choudhary, S. ; Consiglio, L. ; Flammini, A. ; Galbiati, C. ; Ghiano, C. ; Gola, A. ; Horikawa, S. ; et al ( December 2021 , The European Physical Journal C)

   Abstract A large number of particle detectors employ liquid argon as their target material owing to its high scintillation yield and its ability to drift ionization charge over large distances. Scintillation light from argon is peaked at 128 nm and a wavelength shifter is required for its efficient detection. In this work, we directly compare the light yield achieved in two identical liquid argon chambers, one of which is equipped with polyethylene naphthalate (PEN) and the other with tetraphenyl butadiene (TPB) wavelength shifter. Both chambers are lined with enhanced specular reflectors and instrumented with SiPMs with a coverage fraction of approximately 1%, which represents a geometry comparable to the future large scale detectors. We measured the light yield of the PEN chamber to be  39.4 $$\,\pm \,$$ ± 0.4(stat) $$\,\pm \,$$ ± 1.9(syst)% of the yield of the TPB chamber. Using a Monte Carlo simulation this result is used to extract the wavelength shifting efficiency of PEN relative to TPB equal to 47.2 $$\,\pm \,$$ ± 5.7%. This result paves the way for the use of easily available PEN foils as a wavelength shifter, which can substantially simplify the construction of future liquid argon detectors. 

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3. Performance of a Modular Ton-Scale Pixel-Readout Liquid Argon Time Projection Chamber

   https://doi.org/10.3390/instruments8030041  

   Abed_Abud, A ; Abi, B ; Acciarri, R ; Acero, M A ; Adames, M R ; Adamov, G ; Adamowski, M ; Adams, D ; Adinolfi, M ; Adriano, C ; et al ( September 2024 , Instruments)

   The Module-0 Demonstrator is a single-phase 600 kg liquid argon time projection chamber operated as a prototype for the DUNE liquid argon near detector. Based on the ArgonCube design concept, Module-0 features a novel 80k-channel pixelated charge readout and advanced high-coverage photon detection system. In this paper, we present an analysis of an eight-day data set consisting of 25 million cosmic ray events collected in the spring of 2021. We use this sample to demonstrate the imaging performance of the charge and light readout systems as well as the signal correlations between the two. We also report argon purity and detector uniformity measurements and provide comparisons to detector simulations. 

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4. R &D of wavelength-shifting reflectors and characterization of the quantum efficiency of tetraphenyl butadiene and polyethylene naphthalate in liquid argon

   https://doi.org/10.1140/epjc/s10052-022-10383-0  

   Araujo, G. R. ; Baudis, L. ; McFadden, N. ; Krause, P. ; Schönert, S. ; Wu, V. H. ( May 2022 , The European Physical Journal C)

   Abstract Detectors based on liquid argon (LAr) often require surfaces that can shift vacuum ultraviolet (VUV) light and reflect the visible shifted light. For the LAr instrumentation of the LEGEND-200 neutrinoless double beta decay experiment, several square meters of wavelength-shifting reflectors (WLSR) were prepared: the reflector Tetratex® (TTX) was in-situ evaporated with the wavelength shifter tetraphenyl butadiene (TPB). For even larger detectors, TPB evaporation will be more challenging and plastic films of polyethylene naphthalate (PEN) are considered as an option to ease scalability. In this work, we first characterized the absorption (and reflectivity) of PEN, TPB (and TTX) films in response to visible light. We then measured TPB and PEN coupled to TTX in a LAr setup equipped with a VUV sensitive photomultiplier tube. The effective VUV photon yield in the setup was first measured using an absorbing reference sample, and the VUV reflectivity of TTX quantified. The characterization and simulation of the setup along with the measurements and modelling of the optical parameters of TPB, PEN and TTX allowed to estimate the absolute quantum efficiency (QE) of TPB and PEN in LAr (at 87K) for the first time: these were found to be above 67 and 49%, respectively (at 90% CL). These results provide relevant input for the optical simulations of experiments that use TPB in LAr, such as LEGEND-200, and for experiments that plan to use TPB or PEN to shift VUV scintillation light. 

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5. Separation of track- and shower-like energy deposits in ProtoDUNE-SP using a convolutional neural network

   https://doi.org/10.1140/epjc/s10052-022-10791-2  

   Abed Abud, A. ; Abi, B. ; Acciarri, R. ; Acero, M. A. ; Adames, M. R. ; Adamov, G. ; Adamowski, M. ; Adams, D. ; Adinolfi, M. ; Aduszkiewicz, A. ; et al ( October 2022 , The European Physical Journal C)

   Abstract Liquid argon time projection chamber detector technology provides high spatial and calorimetric resolutions on the charged particles traversing liquid argon. As a result, the technology has been used in a number of recent neutrino experiments, and is the technology of choice for the Deep Underground Neutrino Experiment (DUNE). In order to perform high precision measurements of neutrinos in the detector, final state particles need to be effectively identified, and their energy accurately reconstructed. This article proposes an algorithm based on a convolutional neural network to perform the classification of energy deposits and reconstructed particles as track-like or arising from electromagnetic cascades. Results from testing the algorithm on experimental data from ProtoDUNE-SP, a prototype of the DUNE far detector, are presented. The network identifies track- and shower-like particles, as well as Michel electrons, with high efficiency. The performance of the algorithm is consistent between experimental data and simulation. 

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