Session T12: Instrumentation IV

The Physics of Extremely Low Energy Nuclear Recoils for Dark Matter and Coherent Neutrino Scattering

Direct detection of dark matter and detection of neutrinos via coherent scattering (CENNS) are venues in which we are interested in detecting extremely low energy nuclear recoils. While these nuclear recoils are difficult to detect, there has been much recent progress in this area. I survey some of the most recent work on the subject including the use of thermal neutron scattering to produce controlled nuclear recoil events at around 100 eV recoil energy. We also discuss how thermal neutrons can also pose background issues for dark matter and CENNS in the case where the flux is unknown.

    

Characterizing a p-type Ge detector operated at cryogenic temperature by measuring the binding energy of cluster dipole states for low-mass dark matter searches

We have studied the potential application of a p-type Ge detector operated at cryogenic temperature (at 5.2 K) for low-mass dark matter searches. By measuring the binding energies of cluster dipole states as a function of the applied electric field, the detector is operated in two different modes:

The first mode is that the detector is depleted at 77 K and then decreases the temperature to 5.2 K.

The second mode is that the detector is directly cooled down to 5.2 K.

In the two modes, the detector is exposed to an Am-241 source, which emits alphas with an energy of 5.5 MeV. It has been observed that the binding energy of cluster dipole states is lower in the second mode than in the first mode. The binding energy of the cluster dipole states in this p-type Ge detector is found in the range of ~ 4-8 meV. Such a small energy indicated that this detector can be used to study low-mass dark matter.

    

Characterization of the binding energy of cluster dipole states in an n-type germanium detector operated at cryogenic temperature for low-mass dark matter searches.

We have studied the application of n-type germanium detectors operated at 5.2 K for low-mass dark matter searches.  The characterization of the detector is through measuring the binding energy of cluster dipole states.  The detector is operated in two different modes: the first method is to deplete the detector at 77k and then decrease the temperature to 5.2K and the second method is directly to decrease the detector temperature to 5.2 k and then apply different bias voltages. It is found that the binding energy of cluster dipole states is lower in the second method than in the first method. It indicates the different charge states, to begin with in the detector. The binding energy of the trapped charge carriers in cluster dipole states is found in the range of ~5-8 meV. Such small binding energy allows the charge to be released by absorbing very small energy from low-mass dark matter interacting with Ge atoms.

 

    

Measuring Quasiparticle Diffusion in Superconducting Aluminum Films with a TES and Microscopic Laser-Scanning Technique

We present preliminary data from a laser-scanning microscopy-based technique for measuring 100µm-scale quasiparticle (QP) diffusion in superconducting Al films. QP are produced at a localized origin in the Al film using a focused 1550nm laser coupled to a single-mode optical fiber mounted on piezoelectric nanopositioners. The resulting QP propagation can then be monitored using a transition edge sensor (TES), and described using a simple diffusion model.   

Quantum Sensors for Dark Matter Detection

Developments over the last decade have pushed the search for particle dark matter (DM) to new frontiers, including the keV-scale lower mass limit for thermally-produced DM. Galactic DM at this mass is kinematically matched with the energy needed to break a Cooper pair in common superconductors (~meV). Quantum sensors that are sensitive to these broken Cooper pairs can potentially be exploited as low-threshold detectors for particle-like DM scattering. The Quantum Science Center group at Fermilab is using two test facilities to pursue development of such quantum sensors for DM detection. A surface facility, LOUD, has been commissioned and is currently being operated to explore the capabilities of a variety of quantum sensors as elements of novel low-mass DM detection schemes. A dedicated underground partner facility, QUIET, is currently being commissioned and will be used for operation of select devices in a low-background environment. This talk will discuss recent progress on these facilities and devices tested, and the plans to leverage them for DM detection down to the keV-scale.   

First Nuclear-Recoil Ionization-Yield Measurement Down to 100 eV in Silicon

Direct-detection experiments searching for dark matter-nucleus interactions or coherent elastic neutrino-nucleus scattering often use a charge-based readout and are commonly calibrated using sources interacting with the electrons of the detector. However, nuclear and electron interactions produce a different amount of charges for the same energy deposition. Therefore, the precise knowledge of the nuclear recoil ionization yield – which quantifies the amount of energy involved in generating charge carriers for a given nuclear recoil – is essential for these science measurements. 

A silicon-based SuperCDMS HVeV cryogenic calorimetric detector was operated in a monochromatic neutron beam at the Triangle Universities Nuclear Laboratory (Durham, North Carolina) as part of the IMPACT (Ionization Measurement with Phonons At Cryogenic Temperatures) program. In this talk, we will present results from the first nuclear-recoil ionization yield measurement in silicon down to an energy of 100 eV.   

Author not Attending

Sub-eV threshold particle detectors are an area of burgeoning interest, driven in part by needing to probe the increasingly theoretically relevant sub-GeV mass dark matter parameter space. One such promising technology are qubit derived superconducting charge-parity sensors. These detection schemes include Quantum Capacitance Detectors (QCDs) and Offset-Charge Sensitive (OCS) devices, and the former have been demonstrated in previous literature as excellent far-IR photon counters with NEP of < 10^-20 W/√Hz. We seek to extend the applicability of this technique by directly coupling the sensors to interaction induced athermal phonons generated within a crystalline silicon substrate. Such a scheme will enable the literal counting of quasiparticles (broken Cooper-pair electrons) within the superconducting absorber, as produced by single meV phonons. In this talk we will discuss preliminary charge-parity detector design progress and challenges and lay out a roadmap for demonstrating eV and subsequently lower energy resolution.

    

Studies of the Light Output and Oxygen Penetration Depth of Plastic Scintillators during Irradiation

Results are presented on the decrease of light output for plastic scintillator during irradiation by a Cobalt-60 source at a dose rate of 1.3 Gy/hr and at temperatures of -30, -15, 0, and 10 degrees, wrapped in Tyvek and unwrapped, in standard atmosphere. At -30 degrees C with ESR wrapping, measurements were also made in a 97% nitrogen, 3% oxygen atmosphere and in standard atmosphere. Substantial damage was seen during the -30 degree irradiation with ESR wrapping that annealed quickly when the sample was warmed after the end of irradiation. The damage was less at warmer temperatures. The damage was largest with ESR wrapping and smallest with no wrapping. Damage with 3% oxygen was similar to that in standard atmosphere. Evidence of a plateau in the radical density was seen for the 0 and 10 degree C data. This is the first measurement of damage during irradiation at cold temperatures.