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The Hamamatsu R5912-HQE photomultiplier-tube (PMT) is a novel high-quantum efficiency PMT. It is currently used in the DEAP-3600 dark matter detector and is of significant interest for future dark matter and neutrino experiments where high signal yields are needed. We report on the methods developed for in-situ characterization and monitoring of DEAP's 255 R5912-HQE PMTs. This includes a detailed discussion of typical measured single-photoelectron charge distributions, correlated noise (afterpulsing), dark noise, double, and late pulsing characteristics. The characterization is performed during the detector commissioning phase using laser light injected through a light diffusing sphere and during normal detector operation using LED light injected through optical fibres.

The Hamamatsu R5912-HQE photomultiplier-tube (PMT) is a novel high-quantum efficiency PMT. It is currently used in the DEAP-3600 dark matter detector and is of significant interest for future dark matter and neutrino experiments where high signal yields are needed. We report on the methods developed for in-situ characterization and monitoring of DEAP's 255 R5912-HQE PMTs. This includes a detailed discussion of typical measured single-photoelectron charge distributions, correlated noise (afterpulsing), dark noise, double, and late pulsing characteristics. The characterization is performed during the detector commissioning phase using laser light injected through a light diffusing sphere and during normal detector operation using LED light injected through optical fibres.

The recent discovery that GaAs(Si,B) is a bright cryogenic scintillator with no apparent afterglow offers new opportunities for detecting rare, low-energy, electronic excitations from interacting dark matter. This paper presents Monte Carlo calculations of the scintillation photon detection efficiencies of optical cavities using three current cryogenic photodetector technologies. In order of photon detection efficiency these are: (1) Ge/TES: germanium absorbers that convert interacting photons to athermal phonons that are readout by transition edge sensors, (2) KID: kinetic induction detectors that respond to the breaking of cooper pairs by a change in resonance frequency, and (3) SNSPD: superconducting nanowire single photon detectors, where a photon briefly transitions a thin wire from superconducting to normal. The detection efficiencies depend strongly on the n -type GaAs absolute absorption coefficient K A , which is a part of the narrow beam absorption that has never been directly measured. However, the high cryogenic scintillation luminosity of GaAs(Si,B) sets an upper limit on K A of 0.03/cm. Using that value and properties published for Ge/TES, KID, and SNSPD photodetectors, this work calculates that those photodetectors attached to opposing faces of a 1 cm3 cubic GaAs(Si,B) crystal in an optical cavity with gold mirrors would have scintillation photon detection efficiencies of 35%, 25%, and 8%, respectively. Larger values would be expected for lower values of K A. [ABSTRACT FROM AUTHOR]

The creation and evolution of nonequilibrium phonons is central in applications ranging from cosmological particle searches to decoherence processes in qubits. However, the fundamental understanding of decoherence pathways for athermal phonon distributions in solid-state systems remains an open question. Using first-principles calculations, we investigate the primary decay channels of athermal phonons in two technologically relevant semiconductors-Si and GaAs. We quantify the contributions of anharmonic, isotopic, and interfacial scattering in these materials. From this, we construct a model to estimate the thermal power in a readout scheme as a function of time. We discuss the implication of our results on noise limitations in current phonon sensor designs and strategies for improving coherence in next-generation phonon sensors., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Based on the McCabe-Thiele (M-T) method and the conservation of mass and energy, the PandaX-4T collaboration group designs an efficient cryogenic distillation system to reduce the mole fraction of krypton in commercial xenon from 5×10-7 to 1×10-14. Since the ultra-high purity xenon cryogenic distillation system has completed the offline purification operation, it is necessary to conduct the corresponding operation analysis. Therefore, the stability and purification performance of the ultra-high purity xenon cryogenic distillation system are studied by analyzing the parameters such as temperature, pressure, flowrate, and mole faction of the product xenon in each operating stage. The PandaX-4T cryogenic distillation system has been operating stably for 1.5 m at a collection efficiency of 99% and a purification rate of 10 kg/h, and has purified 5.75 t of xenon. The experimental data show that the system is stable, safe, and reliable in all stages of operation, and the krypton concentration in product xenon is less than 7.99×10-12. The operation analysis of the PandaX-4T ultra-high purity xenon cryogenic distillation system has a theoretical research value and practical engineering significance, providing very important reference for optimization of distillation operation of the next stage.

To meet the requirements of the low background and high sensitivity of the large-scale dark-matter detector PandaX-4T, nKr/nXe≤1×10 -13 (n is the amount of substance) is required. The ultra-high purity krypton/xenon cryogenic distillation tower was used as an example in this paper. First, the distillation tower and the construction design of the distillation system were briefly introduced. Then, the operation parameters of the distillation tower were simulated and optimized by using HYSYS, and the distributions of the pressure, temperature and Kr concentration in the distillation tower were obtained. After that, the influences of those operational conditions including the feeding point position, the reflux ratio, the feeding flowrate, the heat of the reboiler, the flowrate of the off-gas, and the feeding pressure to the xenon purity of the distillation system were studied, and the optimized operation parameters were proposed. When the column pressure is set at 221 kPa and the reflux radio is set at 145, the krypton content in xenon can be purified from 5×10-7 to 4.1×10-14, which has an important guiding significance for further improvement of the purity of the xenon product of the xenon/krypton cryogenic distillation system.

Detection rates for the elastic and inelastic scattering of weakly interacting massive particles (WIMPs) off 23Na are calculated within the framework of Deformed Shell Model (DSM) based on Hartree-Fock states. At first, the spectroscopic properties of the detector nucleus, like energy spectra and magnetic moments, are evaluated and compared with experimental data. Following the good agreement of these results, DSM wave functions are used for obtaining elastic and inelastic spin structure functions, nuclear structure coefficients and so forth for the WIMP-23Na scattering. Then, the event rates are also computed with a given set of supersymmetric parameters. In the same manner, using DSM wavefunctions, nuclear structure coefficients and event rates for elastic scattering of WIMPs from 40Ar are also obtained. These results for event rates and also for annual modulation will be useful for the ongoing and future WIMP detection experiments involving detector materials with 23Na and 40Ar nuclei.

We report progress on the development of a light detector with Neganov–Luke (NL) phonon amplification. Double comb-like electrodes were fabricated on an intrinsic Si wafer to apply an electric field. A metallic magnetic calorimeter was used for a sensitive measurement of the temperature increase originating from the light absorption in the wafer and NL phonon amplification. The NL light detector was applied to the simultaneous detection of heat and light signals from a ZnWO 4 scintillating crystal. Clear amplification of the light signals was obtained for various voltages applied to the electrodes, while no change in the heat signals was observed. The voltage dependence of the measured gain was investigated for a few efficiency parameters, such as the saturation voltage required to suppress the recombination of electron-hole pairs and the heat generation efficiency of the NL effect. [ABSTRACT FROM AUTHOR]

Low energy threshold detectors are necessary in many frontier fields of experimental physics. In particular, these are extremely important for probing possible dark matter (DM) candidates. We present a novel detection approach that exploits the energy levels of atoms maintained at cryogenic temperature. We exploit laser-assisted transitions that are triggered by the absorption of the incident particle in the material and lead to the emission of a fluorescent photon or an electron. In this approach, the incident particle will in fact excite the first low-lying energy level that is then up-converted using an opportune narrow-band laser system. Two different detection schemes are thus possible in our active material: one is based on a photon signal while the other takes advantage of high efficiency in-vacuum charge detection. [ABSTRACT FROM AUTHOR]

Abstract The Hamamatsu R5912-HQE photomultiplier-tube (PMT) is a novel high-quantum efficiency PMT. It is currently used in the DEAP-3600 dark matter detector and is of significant interest for future dark matter and neutrino experiments where high signal yields are needed. We report on the methods developed for in-situ characterization and monitoring of DEAP's 255 R5912-HQE PMTs. This includes a detailed discussion of typical measured single-photoelectron charge distributions, correlated noise (afterpulsing), dark noise, double, and late pulsing characteristics. The characterization is performed during the detector commissioning phase using laser light injected through a light diffusing sphere and during normal detector operation using LED light injected through optical fibres. [ABSTRACT FROM AUTHOR]

This paper describes the use of Feynman photon path integrals to compute the probability of detecting reflected, diffracted, and scattered photons at different points in space after interacting with conduction electrons. Five examples are given: (1) a thin parabolic sheet of conduction electrons (e.g. a metal mirror) that produces a sharp focus of a distant point source surrounded by the Airy diffraction pattern, (2) the loss of focusing power as the thickness of the parabolic sheet is increased and complete destructive interference for thicknesses that are an integer multiple of 1/2 the wavelength, (3) diffraction of photons entering a thin sheet from the side, (4) diffraction of photons entering the side of a sheet as its thickness is increased, and (5) the angular scattering distribution of internally generated photons in an extended volume of conduction electrons. The calculations integrated the complex probability amplitudes for photon paths from (a) a point source to (b) all points in the conduction electron volume and to (c) a point detector. At each detector position the detection probability was computed as the square of the absolute value of the integral. In general, if there is a concentration of paths that have nearly the same complex amplitude phase, reflection dominates. Otherwise, if the conduction electron volume has sharp boundaries, diffraction dominates. Isotropic scattering dominates for conduction electrons distributed throughout an extended volume, and may explain how scintillation photons in cryogenic n -type GaAs can escape total internal reflection trapping, which is essential for its high luminosity. [ABSTRACT FROM AUTHOR]

Abstract Dark matter (DM) interacts with ordinary matter through weakly coupling to nucleons. We analyze the coupling strength for DM-proton and DM-neutron respectively utilizing the available data from the most sensitive experiments, XENON1T and SuperCDMS, for a higher (>10 GeV/ c 2) and a lower mass (<10 GeV/ c 2) range of DM particles. Subsequently, we calculate the coupling strength constrained by the DAMA claim and a similar experiment (KIMS) using CsI. The results indicate that XENON1T and SuperCDMS are almost fully sensitive to the DM-nucleon coupling strength predicted by the Fermi weak interaction in the higher mass range. As a result, XENON1T is sensitive to the expected small energy associated with the DM-nucleon weak interaction and hence XENON1T provides a strong constrain on the effective mass of DM from ∼1 MeV/ c 2 to ∼100 MeV/ c 2 , which excludes the mass range of DM between 10 GeV/ c 2 to 104 GeV/ c 2 from being detected. In the lower mass range, four experiments are all not sensitive to the DM-nucleon coupling strength expected from the Fermi weak interaction. The DM-nucleon coupling strength, (Z f p + N f n) 2 , determined by the DAMA data can be fully ruled out by the most sensitive experiments. This work launches new direction for the current DM experiments to provide the constrains on DM-nucleon coupling strength, which sheds light on DM-nucleon coupling properties between impinging DM particles and target nucleons with null experimental results. [ABSTRACT FROM AUTHOR]

The event detection rates for the Weakly Interacting Massive Particles (WIMP) (a dark matter candidate) are calculated with Ge as the detector. The calculations are performed within the deformed shell model (DSM) based on Hartree-Fock states. First, the energy levels and magnetic moment for the ground state and two low-lying positive parity states for this nucleus are calculated and compared with experiment. The agreement is quite satisfactory. Then the nuclear wave functions are used to investigate the elastic and inelastic scattering of WIMP from Ge; inelastic scattering, especially for the transition, is studied for the first time. The nuclear structure factors which are independent of supersymmetric model are also calculated as a function of WIMP mass. The event rates are calculated for a given set of nucleonic current parameters. The calculation shows that Ge is a good detector for detecting dark matter. [ABSTRACT FROM AUTHOR]

We report a comprehensive study of cosmogenic activation of germanium used for tonne-scale rare event search experiments. The germanium exposure to cosmic rays on the Earth’s surface are simulated with and without a shielding container using Geant4 for a given cosmic muon, neutron, and proton energy spectrum. The production rates of various radioactive isotopes are obtained for different sources separately. We find that fast neutron induced interactions dominate the production rate of cosmogenic activation. Geant4-based simulation results are compared with the calculation of ACTIVIA and the available experimental data. A reasonable agreement between Geant4 simulations and several experimental data sets is presented. We predict that cosmogenic activation of germanium can set limits to the sensitivity of the next generation of tonne-scale experiments. [ABSTRACT FROM AUTHOR]

We present a measurement of the cosmogenic activation in the cryogenic germanium detectors of the EDELWEISS III direct dark matter search experiment. The decay rates measured in detectors with different exposures to cosmic rays above ground are converted into production rates of different isotopes. The measured production rates in units of nuclei/kg/day are 82 ± 21 for 3 H, 2.8 ± 0.6 for 49 V, 4.6 ± 0.7 for 55 Fe, and 106 ± 13 for 65 Zn. These results are the most accurate for these isotopes. A 90% C.L. lower limit on the production rate of 68 Ge of 71 nuclei/kg/day is also presented. They are compared to model predictions present in literature and to estimates calculated with the ACTIVIA code. [ABSTRACT FROM AUTHOR]

On silver halide (AgX) emulsion grains (∼200 nm in diameter) for neutrino detection in OPERA project, a latent image center composed of a cluster of ≧4 Ag atoms is formed with ∼18 electron-hole pairs by current photographic process in each grain. According to the analysis in this paper, AgX emulsion grains (∼40 nm) for dark matter detection should behave quite differently, forming a latent image center under such extraordinary condition that as many as ∼1000 electrons and surplus positive holes are created for ∼10 femtoseconds (fs) in each grain, causing violent recombination and re-halogenation of Ag clusters. Therefore, it is necessary to strongly reduce the recombination and re-halogenation of Ag clusters in the nuclear emulsions for dark matter detection. Further proposals are made on the design of nuclear emulsions for dark matter detection. [ABSTRACT FROM AUTHOR]

We evaluate the cosmogenic production rates in some materials that are commonly used as targets and shielding/supporting components for detecting rare events. The results from Geant4 simulations and the calculations of ACTIVIA are compared with the available experimental data. We demonstrate that the production rates from the Geant4-based simulations agree with the available data reasonably well. As a result, we report that the cosmogenic production of several isotopes in various materials can generate potential backgrounds for direct detection of dark matter and neutrinoless double-beta decay. [ABSTRACT FROM AUTHOR]

We used the internal conversion ( transition) of germanium-72 to indirectly measure the low energy nuclear recoils of germanium. Together with a reliable Monte Carlo package, in which we implement the internal conversion process, the data was compared to the Lindhard (k =0.159) and Barker–Mei models. A shape analysis indicates that both models agree well with data in the region of interest within 4%. The most probable value (MPV) of the nuclear recoils obtained from the shape analysis is 17.5±0.12 (sys) ±0.035 (stat) keV with an average path-length of 0.014 m. [ABSTRACT FROM AUTHOR]

Micromegas is a type of micro-pattern gaseous detector currently under R&D for applications in rare event search experiments. Here we report the performance of a Micromegas structure constructed with a micromesh thermo-bonded to a readout plane, motivated by its potential application in two-phase xenon detectors for dark matter and neutrinoless double beta decay experiments. The study is carried out in pure xenon at room temperature. Measurements with alpha particles from the Americium-241 source showed that gas gains larger than 200 can be obtained at xenon pressure up to 3 atm. Gamma rays down to 8 keV were observed with such a device. [ABSTRACT FROM PUBLISHER]

Abstract: The response of a CdWO4 crystal scintillator to protons, particles, Li, C, O and Ti ions with energies in the range 1–10MeV was measured. The non-proportionality of CdWO4 for low energy electrons (4–110keV) was studied with the Compton Coincidence Technique. The energy dependence of the quenching factors for ions and the relative light yield for low energy electrons was calculated using a semi-empirical approach. Pulse-shape discrimination ability between quanta, protons, particles and ions was investigated. [Copyright &y& Elsevier]

Abstract: The discrepancies in claims of experimental evidence in the search for weakly interacting massive particle (WIMP) dark matter necessitate a model for ionization efficiency (the quenching factor) at energies below 10keV. We have carefully studied the physics processes that contribute to the ionization efficiency through stopping power. The focus of this work is the construction of a model for the ionization efficiency in germanium by analyzing the components of stopping power, specifically that of the nuclear stopping power, at low energies. We find a fraction of the ZBL nuclear stopping power can contribute to ionization efficiency. We propose a model that corrects the missing contribution to ionization efficiency from the ZBL nuclear stopping power. The proposed model is compared to previous measurements of ionization efficiency in germanium as well as that of other theoretical models. Using this new model, the thresholds of both CDMS II and CoGeNT are analyzed and compared in terms of the nuclear recoil energy. [Copyright &y& Elsevier]

Abstract: Neutrons from () reactions through thorium and uranium decays are important sources of background for direct dark matter detection. The neutron yields and energy spectra from a range of materials that are used to build dark matter detectors are calculated and tabulated. In addition to thorium and uranium decays, we found that -particles from samarium, often the dopant of the window materials of photomultiplier tubes (PMT), are also an important source of neutron yield. The results in this paper can be used as the input to Monte Carlo simulations for many materials that will be used for next generation experiments. [Copyright &y& Elsevier]

Abstract: We revisit calculations of the cosmogenic production rates for several long-lived isotopes that are potential sources of background in searching for rare physics processes such as the detection of dark matter and neutrinoless double-beta decay. Using updated cosmic-ray neutron flux measurements, we use TALYS 1.0 to investigate the cosmogenic activation of stable isotopes of several detector targets and find that the cosmogenic isotopes produced inside the target materials and cryostat can result in large backgrounds for dark matter searches and neutrinoless double-beta decay. We use previously published low-background HPGe data to constrain the production of 3H on the surface and the upper limit is consistent with our calculation. We note that cosmogenic production of several isotopes in various targets can generate potential backgrounds for dark matter detection and neutrinoless double-beta decay with a massive detector, thus great care should be taken to limit and/or deal with the cosmogenic activation of the targets. [Copyright &y& Elsevier]

We review what can (and cannot) be learned if dark matter is detected in one or more experiments, emphasizing the importance of combining LHC data with direct, astrophysical and cosmological probes of dark matter. We briefly review the conventional picture of a thermally produced WIMP relic density and its connection with theories of electroweak symmetry breaking. We then discuss both experimental and theoretical reasons why one might generically expect this picture to fail. If this is the case, we argue that a combined effort bringing together all types of data — combined with explicitly constructed theoretical models — will be the only way to achieve a complete understanding of the dark matter in our universe and become confident that any candidate actually provides the relic density. [ABSTRACT FROM AUTHOR]

Abstract: Scintillation efficiency of low-energy nuclear recoils in noble liquids plays a crucial role in interpreting results from some direct searches for weakly interacting massive particle (WIMP) dark matter. However, the cause of a reduced scintillation efficiency relative to electronic recoils in noble liquids remains unclear at the moment. We attribute such a reduction of scintillation efficiency to two major mechanisms: (1) energy loss and (2) scintillation quenching. The former is commonly described by Lindhard’s theory and the latter by Birk’s saturation law. We propose to combine these two to explain the observed reduction of scintillation yield for nuclear recoils in noble liquids. Birk’s constants kB for argon, neon and xenon determined from experimental data are used to predict noble liquid scintillator’s response to low-energy nuclear recoils and low-energy electrons. We find that energy loss due to nuclear stopping power that contributes little to ionization and excitation is the dominant reduction mechanism in scintillation efficiency for nuclear recoils, but that significant additional quenching results from the nonlinear response of scintillation to the ionization density. [Copyright &y& Elsevier]

Dark Matter particles are commonly assumed to be weakly interacting massive particles (WIMPs) with a mass in the GeV to TeV range. However, recent interest has shifted toward lighter WIMPs, which are more difficult to probe experimentally. A detection of sub‐GeV WIMPs will require the use of small gap materials in sensors. Using recent estimates of the WIMP mass, we identify the relevant target space toward small gap materials (100 to 10 meV). Dirac Materials, a class of small‐ or zero‐gap materials, emerge as natural candidates for sensors for Dark Matter detection. We propose the use of informatics tools to rapidly assay materials band structures to search for small gap semiconductors and semimetals, rather than focusing on a few preselected compounds. As a specific example of the proposed strategy, we use the organic materials database (https://omdb.diracmaterials.org) to identify organic candidates for sensors: the narrow band gap semiconductors BNQ‐TTF and DEBTTT with gaps of 40 and 38 meV, and the Dirac‐line semimetal (BEDT‐TTF)·Br which exhibits a tiny gap of ≈50 meV when spin‐orbit coupling is included. We outline a novel and powerful approach to search for dark matter detection sensor materials by means of a rapid assay of materials using informatics tools. Specific properties for potential sensor materials for dark matter detection are defined. A materials informatics approach is discussed on the example of the organic materials database OMDB. Three potential candidate materials are identified. Two materials are tiny gap semiconductors. The third is a Dirac‐line semimetal which gaps out under the tiny spin‐orbit coupling present in the material. [ABSTRACT FROM AUTHOR]