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1. The DAMIC-M Low Background Chamber

   https://doi.org/10.1088/1748-0221/19/11/T11010  

   Arnquist, I; Avalos, N; Bailly, P; Baxter, D; Bertou, X; Bogdan, M; Bourgeois, C; Brandt, J; Cadiou, A; Castelló-Mor, N; et al (November 2024, Journal of Instrumentation)

   Abstract The DArk Matter In CCDs at Modane (DAMIC-M) experiment is designed to search for light dark matter (m_χ< 10 GeV/c²) at the Laboratoire Souterrain de Modane (LSM) in France. DAMIC-M will use skipper charge-coupled devices (CCDs) as a kg-scale active detector target. Its single-electron resolution will enable eV-scale energy thresholds and thus world-leading sensitivity to a range of hidden sector dark matter candidates. A DAMIC-M prototype, the Low Background Chamber (LBC), has been taking data at LSM since 2022. The LBC provides a low-background environment, which has been used to characterize skipper CCDs, study dark current, and measure radiopurity of materials planned for DAMIC-M. It also allows testing of various subsystems like readout electronics, data acquisition software, and slow control. This paper describes the technical design and performance of the LBC. 

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2. nEXO: neutrinoless double beta decay search beyond 10 ²⁸ year half-life sensitivity

   https://doi.org/10.1088/1361-6471/ac3631  

   Adhikari, G; Al Kharusi, S; Angelico, E; Anton, G; Arnquist, I J; Badhrees, I; Bane, J; Belov, V; Bernard, E P; Bhatta, T; et al (December 2021, Journal of Physics G: Nuclear and Particle Physics)

   Abstract The nEXO neutrinoless double beta (0 νββ ) decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in 136 Xe. Progress in the detector design, paired with higher fidelity in its simulation and an advanced data analysis, based on the one used for the final results of EXO-200, produce a sensitivity prediction that exceeds the half-life of 10 28 years. Specifically, improvements have been made in the understanding of production of scintillation photons and charge as well as of their transport and reconstruction in the detector. The more detailed knowledge of the detector construction has been paired with more assays for trace radioactivity in different materials. In particular, the use of custom electroformed copper is now incorporated in the design, leading to a substantial reduction in backgrounds from the intrinsic radioactivity of detector materials. Furthermore, a number of assumptions from previous sensitivity projections have gained further support from interim work validating the nEXO experiment concept. Together these improvements and updates suggest that the nEXO experiment will reach a half-life sensitivity of 1.35 × 10 28 yr at 90% confidence level in 10 years of data taking, covering the parameter space associated with the inverted neutrino mass ordering, along with a significant portion of the parameter space for the normal ordering scenario, for almost all nuclear matrix elements. The effects of backgrounds deviating from the nominal values used for the projections are also illustrated, concluding that the nEXO design is robust against a number of imperfections of the model. 

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3. HighNESS conceptual design report: Volume II. The NNBAR experiment.

   https://doi.org/10.3233/JNR-230951  

   Santoro, V; Abou El Kheir, O; Acharya, D; Akhyani, M; Andersen, KH; Barrow, J; Bentley, P; Bernasconi, M; Bertelsen, M; Beßler, Y; et al (May 2024, Journal of Neutron Research)

   A key aim of the HighNESS project for the European Spallation Source is to enable cutting-edge particle physics experiments. This volume presents a conceptual design report for the NNBAR experiment. NNBAR would exploit a new cold lower moderator to make the first search in over thirty years for free neutrons converting to anti-neutrons. The observation of such a baryon-number-violating signature would be of fundamental significance and tackle open questions in modern physics, including the origin of the matter-antimatter asymmetry. This report shows the design of the beamline, supermirror focusing system, magnetic and radiation shielding, and anti-neutron detector necessary for the experiment. A range of simulation programs are employed to quantify the performance of the experiment and show how background can be suppressed. For a search with full background suppression, a sensitivity improvement of three orders of magnitude is expected, as compared with the previous search. Civil engineering studies for the NNBAR beamline are also shown, as is a costing model for the experiment. 

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4. The SABRE experiment for dark matter search

   https://doi.org/10.22323/1.340.0653  

   D'imperio, Giulia; Antonello, M.; Barberio, E.; Baroncelli, T.; Benziger, J.; Bignell, L.J.; Bolognino, I.; Calaprice, F.; Copello, S.; D’Angelo, D.; et al (August 2019, The SABRE experiment for dark matter search)

   The SABRE (Sodium-iodide with Active Background REjection) experiment is a new detector based on NaI(Tl) scintillating crystals for the dark matter detection through the annual modulation. With ultra-pure crystals and an active veto system, based on liquid scintillator surrounding the crystal array, SABRE will reach unprecedented low background and the highest sensitivity among the present NaI(Tl) experiments. Moreover SABRE will be the first dark matter search with twin detectors located in the North and South hemispheres, in Gran Sasso National Laboratories (LNGS), Italy, and Stawell Underground Laboratories (SUPL), Australia, respectively. The double location will help to quantify possible seasonal effects, and is a unique feature to identify a modulation of dark matter origins. SABRE is presently in the Proof-of-Principle (PoP) phase, with the goal to measure the crystal intrinsic and cosmogenic backgrounds of one 5 kg crystal and the active veto efficiency. We have performed a full geometry Monte Carlo simulation in order to evaluate the background contributions in the two distinct operation modes foreseen for the PoP: the potassium Measurement Mode (KMM) and the Dark Matter Measurement Mode (DMM), where the liquid scintillator detector is used in coincidence or anti-coincidence with the crystal, respectively. This paper presents the results of a detailed background simulation and the expected sensitivity for the SABRE full scale experiment. 

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5. Effect of the high-level trigger for detecting long-lived particles at LHCb

   https://doi.org/10.3389/fdata.2022.1008737  

   Calefice, Lukas; Hennequin, Arthur; Henry, Louis; Jashal, Brij; Mendoza, Diego; Oyanguren, Arantza; Sanderswood, Izaac; Sierra, Carlos Vázquez; Zhuo, Jiahui (November 2022, Frontiers in Big Data)

   Long-lived particles (LLPs) show up in many extensions of the Standard Model, but they are challenging to search for with current detectors, due to their very displaced vertices. This study evaluated the ability of the trigger algorithms used in the Large Hadron Collider beauty (LHCb) experiment to detect long-lived particles and attempted to adapt them to enhance the sensitivity of this experiment to undiscovered long-lived particles. A model with a Higgs portal to a dark sector is tested, and the sensitivity reach is discussed. In the LHCb tracking system, the farthest tracking station from the collision point is the scintillating fiber tracker, the SciFi detector. One of the challenges in the track reconstruction is to deal with the large amount of and combinatorics of hits in the LHCb detector. A dedicated algorithm has been developed to cope with the large data output. When fully implemented, this algorithm would greatly increase the available statistics for any long-lived particle search in the forward region and would additionally improve the sensitivity of analyses dealing with Standard Model particles of large lifetime, such as K S 0 or Λ 0 hadrons. 

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