Minimizing Backgrounds for the SuperCDMS SNOLAB Dark-Matter Experiment
- South Dakota School of Mines and Technology, Rapid City, SD (United States)
Astronomical and cosmological observations indicate that large amounts of some slowly moving, unseen Dark Matter pervades the universe and outweighs normal matter by a factor of five. The Standard Model of Physics has no contender with the properties of this as-yet-undetected particle, so experimentalists build state-of-the-art radiation detectors to attempt to directly measure this Dark Matter. The Super Cryogenic Dark Matter Search (SuperCDMS) at Snolab is one such experiment, currently being constructed. This experiment uses ultra-cold, superconducting, high-purity silicon and germanium detectors to measure low-energy nuclear recoils from the elastic scattering of Dark Matter. I contributed to the calibration of the energy scale of low-energy nuclear recoils in CDMS II silicon detectors by computing an improved livetime correction for calibration data to verify the Monte Carlo rate normalization. Results indicate that the phonon collection efficiency of nuclear recoils relative to electron recoils is 95.2$$^{+0.9}_{-0.7\%}$$, and the ionization collection efficiency of low-energy nuclear recoils in silicon is lower than Lindhard prediction, consistent with other recent measurements. Backgrounds from the progeny decay of the abundant, naturally-occurring radioactive isotope radon-222 obstruct the sensitivity of essentially every dark-matter search. Radon concentrations in the Snolab cavern would contribute prohibitively large backgrounds if the volume surrounding the detectors were not purged with a low-flow low-radon gas. By measuring the radon diffusion and emanation, we identified acceptable gasket materials for sealing this radon purge, ensuring that the radon-induced backgrounds will be significantly lower than the other experimental backgrounds. A radon emanation system with a gas handling system and low-background radon detector was commissioned and used to measure the radon emanation of the proposed gaskets. A low-cost apparatus was constructed to measure the radon diffusion of gaskets with a commercial radon detector. The sensitivity of future generations of dark-matter detectors are expected to be dominated by long-lived low-energy beta- and alpha-emitting radon daughters such as 210Pb on detector surfaces. I describe simulations indicating the detector could also be used to reduce background from material impurities plaguing rare-event searches, the commissioning of a prototype demonstration detector, and a gas handling system necessary to operate the detector. I demonstrated that the gas handling system reduces the otherwise dominant backgrounds by a factor of 62. This detector will therefore be able to detect 32Si and 210Pb 100 times better than currently available screeners.
- Research Organization:
- Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); South Dakota School of Mines and Technology, Rapid City, SD (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- DOE Contract Number:
- AC02-07CH11359
- OSTI ID:
- 1864234
- Report Number(s):
- FERMILAB-THESIS-2019-37; oai:inspirehep.net:2057312
- Country of Publication:
- United States
- Language:
- English