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1. SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

   https://doi.org/10.1140/epjc/s10052-020-08801-2  

   Aalseth, C. E.; Abdelhakim, S.; Agnes, P.; Ajaj, R.; Albuquerque, I. F.; Alexander, T.; Alici, A.; Alton, A. K.; Amaudruz, P.; Ameli, F.; et al (February 2021, The European Physical Journal C)

   null (Ed.)

   Abstract 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 scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science. 

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2. SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

   https://doi.org/-https://doi.org/10.1140/epjc/s10052-020-08801-2  

   Aalseth, C. E.; et, al (February 2021, European physical journal)

   null (Ed.)

   Abstract: 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 vis- ible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neu- tral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a sili- con photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detec- tion threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science. 

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3. Doping liquid argon with xenon in ProtoDUNE Single-Phase: effects on scintillation light

   https://doi.org/10.1088/1748-0221/19/08/P08005  

   Abed_Abud, A; Abi, B; Acciarri, R; Acero, MA; Adames, MR; Adamov, G; Adamowski, M; Adams, D; Adinolfi, M; Adriano, C; et al (August 2024, Journal of Instrumentation)

   Abstract Doping of liquid argon TPCs (LArTPCs) with a small concentration of xenon is a technique for light-shifting and facilitates the detection of the liquid argon scintillation light. In this paper, we present the results of the first doping test ever performed in a kiloton-scale LArTPC. From February to May 2020, we carried out this special run in the single-phase DUNE Far Detector prototype (ProtoDUNE-SP) at CERN, featuring 720 t of total liquid argon mass with 410 t of fiducial mass. A 5.4 ppm nitrogen contamination was present during the xenon doping campaign. The goal of the run was to measure the light and charge response of the detector to the addition of xenon, up to a concentration of 18.8 ppm. The main purpose was to test the possibility for reduction of non-uniformities in light collection, caused by deployment of photon detectors only within the anode planes. Light collection was analysed as a function of the xenon concentration, by using the pre-existing photon detection system (PDS) of ProtoDUNE-SP and an additional smaller set-up installed specifically for this run. In this paper we first summarize our current understanding of the argon-xenon energy transfer process and the impact of the presence of nitrogen in argon with and without xenon dopant. We then describe the key elements of ProtoDUNE-SP and the injection method deployed. Two dedicated photon detectors were able to collect the light produced by xenon and the total light. The ratio of these components was measured to be about 0.65 as 18.8 ppm of xenon were injected. We performed studies of the collection efficiency as a function of the distance between tracks and light detectors, demonstrating enhanced uniformity of response for the anode-mounted PDS. We also show that xenon doping can substantially recover light losses due to contamination of the liquid argon by nitrogen. 

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4. 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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5. Impact of extreme ultraviolet radiation on the scintillation of pure and xenon-doped liquid argon

   https://doi.org/10.1103/PhysRevD.111.102001  

   Agnes, P; Berger, Q; Bomben, M; Campestrini, M; Caravati, M; Cortez, A_F V; Franco, D; Galbiati, C; Giovanetti, G K; Hessel, T; et al (May 2025, Physical Review D)

   The Xenon-Argon Technology (X-ArT) Collaboration presents a study on the dynamics of pure and xenon-doped liquid argon (LAr) scintillation. Using two types of silicon photomultipliers sensitive to different wavelength ranges, we provide evidence in favor of a contribution from long-lived ( $>10\mathrm{\mu }\mathrm{s}$) extreme ultraviolet (EUV) lines emitted from argon atomic states, which enhances the light yield. This component is present in both pure and xenon-doped LAr, becoming more pronounced at higher xenon concentrations, where it complements the traditional collisional energy transfer process. To explain this mechanism, we develop a comprehensive model of the Xe-doped LAr scintillation process that integrates both collisional and radiative contributions. Additionally, we investigate how xenon doping affects LAr scintillation light yield and pulse shape discrimination. Finally, we hypothesize that the EUV component may explain the emission of spurious electrons, a known challenge in light dark matter searches using noble liquids. By characterizing the scintillation dynamics in Xe-doped LAr, identifying the long-lived EUV component, and exploring the potential origin of spurious electrons, this work lays the groundwork for optimizing detector performance and advancing the design and sensitivity of future noble liquid particle detectors. Published by the American Physical Society2025 

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