PHYSICS PHD DISSERTATION DEFENSE: Wei Ji

Ph.D. Candidate:  Wei Ji

Research Advisor:  Thomas Shutt

Date: Friday, January 18th, 2019
Time: 10:15 a.m.
Location: PAB 102/103

Title: Dark Matter Search and Electron Background Evaluation Testing of a TPC Grid Design

Abstract:
Dark Matter can explain many observations, and therefore has been proposed for many decades but awaits direct detection. One of the most popular candidates for dark matter is Weakly interacting massive particles (WIMPs). We are building the LZ detector, a liquid xenon Time Projection Chamber (TPC), to achieve the highest sensitivity in the world to find the WIMPs via WIMP-nucleon interactions. The LZ TPC consists of grids that will be operated under voltage, which may introduce electron backgrounds that impede our WIMP search.

We manage the backgrounds by building shields to block or tag them, by reducing the radioactive sources to reduce their occurrence, and by using analysis methods to distinguish them. Because backgrounds from multiple electrons that originate from grid wire surfaces of the detector can impede us from finding the WIMPs, we are motivated to build a test detector to study how to reduce this background. We built such a detector to study the electron emission from grid wire surfaces from the electroluminescence scintillation light, and we are able to measure emission currents as low as atto-amperes. We use this detector to study the properties of different grids and which treatments can be used to reduce their electron emission.