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Register a new userLBECA: A Low Background Electron Counting Apparatus for Sub-GeV Dark Matter Detection
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A. Bernstein
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Two-phase noble liquid detectors, with large target masses and effective background reduction, are currently leading the dark matter direct detection for WIMP masses above a few GeV. Due to their sensitivity to single ionized electron signals, these detectors were shown to also have strong constraints for sub-GeV dark matter via their scattering on electrons. In fact, the most stringent direct detection constraints for sub-GeV dark matter down to as low as ~5 MeV come from noble liquid detectors, namely XENON10, DarkSide-50, XENON100 and XENON1T, although these experiments still suffer from high background at single or a few electron level. LBECA is a planned 100-kg scale liquid xenon detector with significant reduction of the single and a few electron background. The experiment will improve the sensitivity to sub-GeV dark matter by three orders of magnitude compared to the current best constraints.
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A promising technology concept for sub-GeV dark matter detection is described, in which low-temperature microcalorimeters serve as the sensors and superfluid $^4$He serves as the target material. A superfluid helium target has several advantageous properties, including a light nuclear mass for better kinematic matching with light dark matter particles, copious production of scintillation light, extremely good intrinsic radiopurity, a high impedance to external vibration noise, and a unique mechanism for observing phonon-like modes via liberation of $^4$He atoms into a vacuum (`quantum evaporation). In this concept, both scintillation photons and triplet excimers are detected using calorimeters, including calorimeters immersed in the superfluid. Kinetic excitations of the superfluid medium (rotons and phonons) are detected using quantum evaporation and subsequent atomic adsorption onto a microcalorimeter suspended in vacuum above the target helium. The energy of adsorption amplifies the phonon/roton signal before calorimetric sensing, producing a gain mechanism that can reduce the techonologys recoil energy threshold below the calorimeter energy threshold. We describe signal production and signal sensing probabilities, and estimate electron recoil discrimination. We then simulate radioactive backgrounds from gamma rays and neutrons. Dark matter - nucleon elastic scattering cross-section sensitivities are projected, demonstrating that even very small (sub-kg) target masses can probe wide regions of as-yet untested dark matter parameter space.
We present the technical design for the SuperCDMS high-voltage, low-mass dark matter detectors, designed to be sensitive to dark matter down to 300 MeV/$c^2$ in mass and resolve individual electron-hole pairs from low-energy scattering events in high-purity Ge and Si crystals. In this paper we discuss some of the studies and technological improvements which have allowed us to design such a sensitive detector, including advances in phonon sensor design and detector simulation. With this design we expect to achieve better than 10 eV (5 eV) phonon energy resolution in our Ge (Si) detectors, and recoil energy resolution below 1eV by exploiting Luke-Neganov phonon generation of charges accelerated in high fields.
Dark Matter experiments are recently focusing their detection techniques in low-mass WIMPs, which requires the use of light elements and low energy threshold. In this context, we present the TREX-DM experiment, a low background Micromegas-based TPC for low-mass WIMP detection. Its main goal is the operation of an active detection mass $sim$0.300 kg, with an energy threshold below 0.4 keVee and fully built with previously selected radiopure materials. This article describes the actual setup, the first results of the comissioning in Ar+2%iC$_4$H$_{10}$ at 1.2 bar and the future updates for a possible physics run at the Canfranc Underground Laboratory in 2016. A first background model is also presented, based on Geant4 simulations and a muon/electron discrimination method. In a conservative scenario, TREX-DM could be sensitive to DAMA/LIBRA and other hints of positive WIMPs signals, with some space for improvement with a neutron/electron discrimination method or the use of other light gases.
Dark Matter experiments are recently focusing their detection techniques in low-mass WIMPs, which requires the use of light elements and low energy threshold. In this context, we describe the TREX-DM experiment, a low background Micromegas-based TPC for low-mass WIMP detection. Its main goal is the operation of an active detection mass $sim$0.3 kg, with an energy threshold below 0.4 keVee and fully built with previously selected radiopure materials. This work describes the commissioning of the actual setup situated in a laboratory on surface and the updates needed for a possible physics run at the Canfranc Underground Laboratory (LSC) in 2016. A preliminary background model of TREX-DM is also presented, based on a Geant4 simulation, the simulation of the detectors response and two discrimination methods: a conservative muon/electron and one based on a neutron source. Based on this background model, TREX-DM could be competitive in the search for low-mass WIMPs. In particular it could be sensitive, e.g., to the low-mass WIMP interpretation of the DAMA/LIBRA and other hints in a conservative scenario.
If Dark Matter is made of Weakly Interacting Massive Particles (WIMPs) with masses below $sim$20 GeV, the corresponding nuclear recoils in mainstream WIMP experiments are of energies too close, or below, the experimental threshold. Gas Time Projection Chambers (TPCs) can be operated with a variety of target elements, offer good tracking capabilities and, on account of the amplification in gas, very low thresholds are achievable. Recent advances in electronics and in novel radiopure TPC readouts, especially micro-mesh gas structure (Micromegas), are improving the scalability and low-background prospects of gaseous TPCs. Here we present TREX-DM, a prototype to test the concept of a Micromegas-based TPC to search for low-mass WIMPs. The detector is designed to host an active mass of $sim$0.300 kg of Ar at 10 bar, or alternatively $sim$0.160 kg of Ne at 10 bar, with an energy threshold below 0.4 keVee, and is fully built with radiopure materials. We will describe the detector in detail, the results from the commissioning phase on surface, as well as a preliminary background model. The anticipated sensitivity of this technique may go beyond current experimental limits for WIMPs of masses of 2-8 GeV.
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