Toward single electron resolution phonon mediated ionization detectors

Abstract

Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of 14 eV ee . CDMSlite is currently the most sensitive experiment to WIMPs of mass ∼5 GeV/c 2 but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a × 2 Luke phonon gain, world best RMS resolution of sigma ∼7 eV ee for 0.25 kg (d=75 mm, h=1 cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25 mm) will reach a resolution of ∼2.8 eV ee . In order to achieve better resolution of ∼ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.

Dark matter astrophysical uncertainties and the neutrino floor

“…1 with uncertainties listed in Table I. In fact with advances in technology currently underway [45] it will be possible for direct detection experiments to make competitive measurements of these neutrino fluxes [46] and even constrain new physics such as the existence of sterile neutrinos [47] or new interactions between neutrinos and nuclei or electrons [48].…”

“…This is also coupled with the fact that advances in technology are more likely to bring about lower threshold detectors than allow exposures in excess of 10 6 ton-years to be achieved (which are required to observe the neutrino floor due to DSNB and atmospheric neutrinos). For instance, a recent work by Mirabolfathi et al [45] outlined how with current advances in technology, ultra-low thresholds down to ∼ 10 eV may be achievable in cryogenic detectors with excellent energy resolution.…”

Probing light mediators at ultralow threshold energies with coherent elastic neutrino-nucleus scattering

“…We assume a 100eVnr threshold for germanium and silicon. While no current technology exists that reaches such thresholds, experimental progress is underway which can conceivably reach these levels in the near future [42]. For example, CDMSlite recently achieved a threshold of 56eVee (electron recoil) [37] and a few hundred eVnr (the exact conversion factor from eVee to eVnr depends on the parameterization for the ionization yield, which is only known to within a factor of a few).…”

CDMS Detector Fabrication Improvements and Low Energy Nuclear Recoil Measurements in Germanium

“…This equates to a handle at which signal:noise can be tuned at will (until detector limitations are reached by the applied voltage). This effect has been utilized by this group to produce detectors with a baseline noise of ∼ 7eV [7], with the theoretical capability of further improvement by incorporating minimal design changes.…”

“…The x-axis spread in energy is due to the solid angle of the detector and the angular dependence of neutron production, resulting in a 0.4% uncertainty based on the target detector and configuration used in this work. The vertical shift is due to uncertainties in the proton energy at the point of the 7 Li(p,n) 7 Be reaction (see Perhaps the most exciting aspect of this search is the evidence that it not only appears to be incredibly abundant (roughly 5 times the abundance of baryonic matter), but the fact that it is expected to exist in our own backyard. These two components immediately raise questions in a scientist's mind: what is it and how can it be detected?…”