UC Berkeley

Over the last 80 years, a preponderance of cosmological evidence points to the existence of a significant portion of non-luminous in the universe. Experiments have shown that this dark matter is composed up of an exotic, undiscovered particle. Many potential models have been proposed to explain the existence of these particles, but the most well-motivated and well-studied of these models posits the existence of Weakly Interacting Massive Particles (WIMPs). These particles are a thermal relic of the big bang and can potentially help resolve currently unanswered questions in particle physics including the Hierarchy problem.

The Cryogenic Dark Matter Search (CDMS) is a direct detection WIMP search. The experiment employs high purity germanium (Ge) semiconductor detectors instrumented with electrodes and Transition Edge Sensors (TES) to measure the ionization and phonon signal from particle interactions. The two signal pathways allow discrimination between electron recoils (ER) and nuclear recoils (NR). SuperCDMS Soudan consists of data taken with 15 IZIP detectors at the Soudan Underground Laboratory between 2012 and 2014. Three main analyses were conducted on this data: CDMSlite, Low Threshold (LT), and High Threshold (HT). The CDMSlite and Low Threshold analyses were optimized for lower mass (<10 GeV) WIMPs over subsets of the available data.

The HT analysis consists of a blind analysis of the data from the 10 functional detectors installed at Soudan. The total exposure for this data was 1694 kg-days. A multivariate method based on a gradient boosted decision tree was used to optimize the fiducial volume of the detectors. Background components from gammas, radon-decay surface events and both radiogenic and cosmogenic neutrons were modeled. Based on a preliminary limit optimization study, the final efficiency corrected exposure will be ~900 kg-days with an expected background of 0.4 events. This corresponds to an expected limit of ~1.3e-44 cm^2 at a mass of 50 GeV.

While not yet entirely complete, the HT analysis represents has built off a large amount that of work that I did during the development and commissioning of the experiment at Soudan. As the primary operator of the Test Facility at UC Berkeley, I was responsible for the detector characterization and selection testing that both determined which detectors were included in the final payload, but also established the justification for multiple detector modifications that significantly improved both production and operation of the IZIP detectors. Then as one of the members of the collaboration with the most hands on experience operating the IZIPs, I was involved in most aspects of installing and commissioning the detectors that were used to set the world leading low mass limits in addition to the High mass reach currently nearing completion.