A Search For Weakly Interacting Massive Particles Utilizing A Profile Likelihood Ratio Technique With The Super CDMS Soudan Experiment

Thesis/Dissertation · Sat Dec 31 23:00:00 EST 2016

OSTI ID:1864240

Qiu, Hang ^[1]

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1. Southern Methodist U.

Dark matter accounts for ~26.8% of the universe’s mass and ~85% of the matter of the universe. The majority of dark matter is in the form of non-baryonic dark matter. Among all the dark matter particle candidates, the Weakly Interacting Massive Particle (WIMP) is considered the most promising. Tens of experiments around the world are under the searches of WIMPs. The Super Cryogenic Dark Matter Search (SuperCDMS) is one of the leading direct dark matter search experiments. Its latest experiment was located in the Soudan Underground Laboratory in northern Minnesota. By placing its germanium (Ge) detectors deep underground, it aimed at performing a rare-event search in the case that a WIMP would collide with a Ge nucleus and leave a Ge nuclear recoil signal in the detectors. These Ge detectors were operated at a temperature of ~50 mK to reduce the noise from disturbing the ionization and phonon signal collections. A high mass WIMP search analysis is performed on the recent collected data sets at Soudan. It aims at exploring WIMPs with masses from the order of 10 GeV/c² and above. With a raw exposure of 1657.54 kg-days, an exclusion limit is set on the spin-independent WIMP-nucleon cross section at 1.32 ×10^-44 cm² for a 75 GeV/c2 WIMP at a 90% confidence level by the profile likelihood ratio technique. Neutrons are the most dangerous background in a direct dark matter search experiment. The nuclear recoil signal that a neutron produces in a Ge detector is indistinguishable from vii that a WIMP produces. Protection against them is one of the key aspects for the next generation of SuperCDMS experiment at SNOLAB. An active neutron veto system was proposed to be implemented in this future experiment to make it more robust from neutrons. The feasibility of both the plastic and liquid neutron veto systems was studied.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
• DOE Contract Number: AC02-07CH11359
• OSTI ID: 1864240
• Report Number(s): FERMILAB-THESIS-2017-40; oai:inspirehep.net:2057309
• Country of Publication: United States
• Language: English