October 1, 2016.
Dark matter is an unknown type of matter that composes roughly 27% of the observable universe and, as cosmological structure models suggest, the earth should be passing through a “dark halo” of this unknown matter present in the Milky Way galaxy. As we pass through this halo, the Super Cryogenic Dark Matter Search (SuperCDMS) experiment aims to directly detect dark -matter particles. Though many dark matter particle candidates exist, SuperCDMS focuses on the detection of particles called WIMPS (weakly interacting massive particles) as predicted by super-symmetric theories beyond the standard model. Due to the high-sensitivity of the germanium detectors employed, shielding from cosmic rays is paramount, thus the measurements will be performed 6561 feet below ground at SNOLAB. While the experiment will be performed underground, fabrication of the germanium detectors will occur above ground. During this fabrication period, the germanium detectors are exposed to cosmic ray secondaries (i.e., neutrons, protons, and muons). These high-energy secondary particles can interact with the germanium nuclei in the detector crystals through a spallation process that breaks apart the nuclei resulting in unstable products. Of particular concern is the production of tritum that has a ling, 12 year half-life. The eventual beta decay of tritium will create a background contribution that diminishes the sensitivity to WIMP detection. A goal of this work is to model and predict cosmogenic exposure at the fabrication sites to account for this tritium production. Expected integrated cosmic ray fluxes were derived for three cosmic ray particles: secondary muons, protons, and neutrons, at ten different fabrication and experimental sites involved in the SuperCDMS experiment. In addition to the cosmic ray fluxes, location and time depend cosmic ray attenuation parameters were developed to account for three main variables: elevation, position with respect to the earth’s magnetic field, as well as time of exposure with respect to the sun’s 11 year solar cycle. In addition, for each of the ten fabrication sites a CRY simulation was developed and run to predict the constituent cosmic ray flux for each particle. A portable cosmic-ray muon detector will be shipped to each site to gather cosmic-ray exposure to confirm these predictions. This detector was assembled and cosmic ray fluxes were measured above ground at PNNL as well as in PNNL’s shallow underground laboratory.
Elementary Particles and Fields and String Theory | Other Astrophysics and Astronomy
Pacific Northwest National Laboratory (PNNL)
This material is based upon work supported by the National Science Foundation through the Robert Noyce Teacher Scholarship Program under grant# 1546150. Any opinions, finding, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. The research was made possible by the California State University STEM Teacher Researcher Program