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1. Exotic Dark Matter Search with the Majorana Demonstrator

   https://doi.org/10.1103/PhysRevLett.132.041001  

   Arnquist, I J ; Avignone, F T ; Barabash, A S ; Barton, C J ; Bhimani, K H ; Blalock, E ; Bos, B ; Busch, M ; Buuck, M ; Caldwell, T S ; et al ( January 2024 , Physical Review Letters)

   With excellent energy resolution and ultralow-level radiogenic backgrounds, the high-purity germanium detectors in the Majorana Demonstrator enable searches for several classes of exotic dark matter (DM) models. In this work, we report new experimental limits on keV-scale sterile neutrino DM via the transition magnetic moment from conversion to active neutrinos 𝜈𝑠→𝜈𝑎. We report new limits on fermionic dark matter absorption (𝜒+𝐴→𝜈+𝐴) and sub-GeV DM-nucleus 3→2 scattering (𝜒+𝜒+𝐴→𝜙+𝐴), and new exclusion limits for bosonic dark matter (axionlike particles and dark photons). These searches utilize the (1–100)-keV low-energy region of a 37.5-kg y exposure collected by the Demonstrator between May 2016 and November 2019 using a set of 76Ge-enriched detectors whose surface exposure time was carefully controlled, resulting in extremely low levels of cosmogenic activation. 

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2. The Majorana Demonstrator readout electronics system

   https://doi.org/10.1088/1748-0221/17/05/T05003  

   Abgrall, N. ; Amman, M. ; Arnquist, I.J. ; Avignone, F.T. ; Barabash, A.S. ; Barton, C.J. ; Barton, P.J. ; Bertrand, F.E. ; Bhimani, K.H. ; Bos, B. ; et al ( May 2022 , Journal of Instrumentation)

   Abstract The Majorana Demonstrator comprises two arrays of high-purity germanium detectors constructed to search for neutrinoless double-beta decay in 76 Ge and other physics beyond the Standard Model. Its readout electronics were designed to have low electronic noise, and radioactive backgrounds were minimized by using low-mass components and low-radioactivity materials near the detectors. This paper provides a description of all components of the Majorana Demonstrator readout electronics, spanning the front-end electronics and internal cabling, back-end electronics, digitizer, and power supplies, along with the grounding scheme. The spectroscopic performance achieved with these readout electronics is also demonstrated. 

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3. SALT-RSS Multiobject Spectroscopic Data Reduction to Reveal Physical Properties of [O ii]-emitting Galaxies from HETDEX and ODIN

   https://doi.org/10.3847/2515-5172/ad4645  

   Kharchilava, George V. ; Gawiser, Eric ; Herrera, Danisbel ; Firestone, Nicole ; Ciardullo, Robin ; Gronwall, Caryl ; Lee, Kyoung-Soo ; Ramakrishnan, Vandana ; Valdes, Francisco ; Yang, Yujin ( May 2024 , Research Notes of the AAS)

   Line flux ratios from [O ii] doublets can probe electron densities in the interstellar medium of galaxies. We employ the Southern African Large Telescope’s (SALT) Robert Stobie Spectrograph (RSS), which provides sufficient resolution (R ∼ 3000) to split the [O ii] doublets, to target galaxies from Hobby-Eberly Telescope Dark Energy Experiment and One-hundred-deg²DECam Imaging in Narrowbands with emission line fluxes of at least 2 × 10⁻¹⁶ erg cm⁻² s⁻¹. Reduction is carried out using RSSMOSPipeline to reduce SALT-RSS data through wavelength calibration. Despite SALT-RSS being known for its difficulty to flux calibrate, we present spectra that have been flux calibrated using alignment stars with Sloan Digital Sky Survey spectra as standards. We combine multiple spectroscopic settings to obtain full 2D spectra across a wavelength range of 3500–9500 Å. A 1D spectrum can then be extracted to calculate flux ratios and line widths, revealing important physical properties of these bright [O ii]-emitters.

    

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4. Exploring the Potential of Residual Impurities in Germanium Detectors for MeV-Scale Dark Matter Detection

   https://doi.org/10.1007/s10909-024-03059-4  

   Mei, Dongming ( March 2024 , Journal of Low Temperature Physics)

   The direct detection of MeV-scale dark matter (DM) particles hinges on achieving an exceptionally low-energy detection threshold. Germanium (Ge) detectors, meticulously tailored with precise impurity compositions, hold the potential to enhance sensitivity to energy levels below the sub-electronvolt (sub-eV) range. This study explores the behavior of residual impurities inherent to Ge detectors at helium temperatures, unveiling a captivating freeze-out phenomenon leading to the formation of excited localized states known as dipole states. Using compelling evidence from relative capacitance measurements obtained from two detectors, we elucidate the transition of impurity atoms from free charge states to these dipole states as the temperature drops from 11 to 6.5 K. Our investigation comprehensively covers the intricate formation of these dipole states in bothn-type andp-type impurities. Furthermore, we shed light on the electric field generated by these dipole states, revealing their ability to trap charges and facilitate the creation of cluster dipole states. Confirming findings from previous measurements, we establish that these excited dipole states exhibit a binding energy of less than 10 meV, offering an exceptionally low detection threshold for MeV-scale DM. Building upon this concept, we propose the development of a 1-kg Ge detector with internal charge amplification—an innovative approach poised to surpass electrical noise and enable the detection of MeV-scale DM with unprecedented sensitivity.

    

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5. First demonstration of 30 eVee ionization energy resolution with Ricochet germanium cryogenic bolometers

   https://doi.org/10.1140/epjc/s10052-024-12433-1  

   Augier, C. ; Baulieu, G. ; Belov, V. ; Bergé, L. ; Billard, J. ; Bres, G. ; Bret, J. -. ; Broniatowski, A. ; Calvo, M. ; Cazes, A. ; et al ( February 2024 , The European Physical Journal C)

   The futureRicochetexperiment aims to search for new physics in the electroweak sector by measuring the Coherent Elastic Neutrino-Nucleus Scattering process from reactor antineutrinos with high precision down to the sub-100 eV nuclear recoil energy range. While theRicochetcollaboration is currently building the experimental setup at the reactor site, it is also finalizing the cryogenic detector arrays that will be integrated into the cryostat at the Institut Laue Langevin in early 2024. In this paper, we report on recent progress from the Ge cryogenic detector technology, called the CryoCube. More specifically, we present the first demonstration of a 30 eVee (electron equivalent) baseline ionization resolution (RMS) achieved with an early design of the detector assembly and its dedicated High Electron Mobility Transistor (HEMT) based front-end electronics with a total input capacitance of about 40 pF. This represents an order of magnitude improvement over the best ionization resolutions obtained on similar phonon-and-ionization germanium cryogenic detectors from the EDELWEISS and SuperCDMS dark matter experiments, and a factor of three improvement compared to the first fully-cryogenic HEMT-based preamplifier coupled to a CDMS-II germanium detector with a total input capacitance of 250 pF. Additionally, we discuss the implications of these results in the context of the futureRicochetexperiment and its expected background mitigation performance.

    

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