Observations of galaxies, superclusters, distant supernovae, and the cosmic microwave background radiation tell us that ~85% of the matter in the universe is made of unknown particles. Understanding the nature and properties of dark matter is fundamental for furthering the fields of cosmology, astrophysics, and particle physics and for shaping our understanding of the makeup of the Universe. A leading theoretical candidate for this dark matter is a class of particles known as Weakly Interacting Massive Particles (WIMPs), which would have been produced at the time of the Big Bang. Experimental efforts to detect these particles via their scattering from atomic nuclei have significantly matured and are possibly within a few years of making a definitive detection. The Cryogenic Dark Matter Search (CDMS) Collaboration has pioneered the use of low temperature phonon-mediated detectors to detect the rare WIMP interactions and distinguish them from backgrounds.
This award will provide support for the continuation of the University of Florida's efforts in terms of supporting the operation and data analysis of the SuperCDMS Soudan experiment, performing detailed R&D into detector response to electron recoil backgrounds, both empirically and via simulation, and supporting the detector characterization and testing program for devices intended to be deployed in the proposed SuperCDMS SNOLAB experiment at SNOLAB.
Broader impacts: The SuperCDMS experiment has had a broad impact which extends beyond the dark matter search. The technical development will further advance phonon-mediated detectors, which have already found many applications in cosmology, astronomy and industry. This work will contribute to the training of graduate students, using techniques at the leading edge of measurement technologies.
The goals of this project were to implement the following procedures in the Geant4 simulation package: 1. Properly define a geometrically complex electric field in a crystal 2. Oblique electron-hole propagation in a crystal under the influence of an electric field, and 3. Emmission of Neganov-Luke phonons by the propagating charges. The propagation of charges in a lattice is typically determined using mass tensor, rather than a scalar, since the the energy/momentum relationships differ based on the direciton of motion with respect to the lattice. Since the Geant4 Monte-Carlo was originally created to track the propagation of high energy particles in vacuum, where the mass of a particle can be treated as a scalar, the fundamental building blocks of the software which are responsible for ensuring proper energy and momentum variation in time/space were built on that assumption. Correctly implementing the energy/momentum relationships of a particle in a lattice required the creation of an intermediary function that translates the instantaneous energy/momentum/effective (tensor) mass quantities of the charged particle to mathematically equivalent scalar values which can be used by the rest of the Geant4 propagation routines. The abovementioned goals were succesfully achieved. The rates of these physical processes was verified by comparing the drift time for electrons and holes in an elecectric field with measured data. The set of routines which handle the propagation of particels (electrons/holes/phonons) in a crystal lattice will be released as a "physics package" titled G4CMP for use by the general physica community. The results of this project were presented at two scientific conferences and submitted for publication in a refereed journal. A graduate student has the opporunity to interact with and learn from scientists at SLAC & Stanfordwho are experts in the area of simulations and low temperature condensed matter physics.
