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1. Scintillation and optical properties of xenon-doped liquid argon

   https://doi.org/10.1088/1748-0221/17/01/C01031  

   Vogl, C.; Schwarz, M.; Stribl, X.; Grießing, J.; Krause, P.; Schönert, S. (January 2022, Journal of Instrumentation)

   Abstract Liquid argon (LAr) is a common choice as detection medium in particle physics and rare-event searches. Challenges of LAr scintillation light detection include its short emission wavelength, long scintillation time and short attenuation length. The addition of small amounts of xenon to LAr is known to improve the scintillation and optical properties. We present a characterization campaign on xenon-doped liquid argon (XeDLAr) with target xenon concentrations ranging from 0 to 300 ppm by mass encompassing the measurement of the photoelectron yield Y , effective triplet lifetime τ 3 and effective attenuation length λ att . The measurements were conducted in the Subterranean Cryogenic ARgon Facility, Scarf , a 1 t (XeD)LAr test stand in the shallow underground laboratory (UGL) of TU-Munich. These three scintillation and optical parameters were observed simultaneously with a single setup, the Legend Liquid Argon Monitoring Apparatus, Llama . The actual xenon concentrations in the liquid and gaseous phases were determined with the Impurity DEtector For Investigation of Xenon, Idefix , a mass spectrometer setup, and successful doping was confirmed. At the highest dopant concentration we find a doubling of Y , a tenfold reduction of τ 3 to ∼90 ns and a tenfold increase of λ att to over 6 m. 

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2. 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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3. 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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4. Development of a ¹²⁷ Xe calibration source for nEXO

   https://doi.org/10.1088/1748-0221/17/07/P07028  

   Lenardo, B.G.; Hardy, C.A.; Tsang, R.H.M.; Nzobadila Ondze, J.C.; Piepke, A.; Triambak, S.; Jamil, A.; Adhikari, G.; Al Kharusi, S.; Angelico, E.; et al (July 2022, Journal of Instrumentation)

   Abstract We study a possible calibration technique for the nEXO experiment using a 127 Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay (0 νββ ) that will use a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in 136 Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of 127 Xe and its small Q-value compared to that of 136 Xe 0 νββ would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC. 

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5. The EXO-200 detector, part II: auxiliary systems

   https://doi.org/10.1088/1748-0221/17/02/P02015  

   Ackerman, N.; Albert, J.; Auger, M.; Auty, D.J.; Badhrees, I.; Barbeau, P.S.; Bartoszek, L.; Baussan, E.; Belov, V.; Benitez-Medina, C.; et al (February 2022, Journal of Instrumentation)

   Abstract The EXO-200 experiment searched for neutrinoless double-beta decay of 136 Xe with a single-phase liquid xenon detector. It used an active mass of 110 kg of 80.6%-enriched liquid xenon in an ultra-low background time projection chamber with ionization and scintillation detection and readout. This paper describes the design and performance of the various support systems necessary for detector operation, including cryogenics, xenon handling, and controls. Novel features of the system were driven by the need to protect the thin-walled detector chamber containing the liquid xenon, to achieve high chemical purity of the Xe, and to maintain thermal uniformity across the detector. 

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