Advancing the Search for Dark Matter: from CDMS II to SuperCDMS

Abstract

An overwhelming proportion of the universe (83% by mass) is composed of particles we know next to nothing about. Detecting these dark matter particles directly, through hypothesized weak-force-mediated recoils with nuclear targets here on earth, could shed light on what these particles are, how they relate to the standard model, and how the standard model fits within a more fundamental understanding.This thesis describes two such experimental efforts: CDMS 11 (2007-2009) and SuperCDMS Soudan (ongoing). The general abilities and sensitivities of both experiments are laid out, placing a special emphasis on the detector technology, and how this technology has evolved from the first to the second experiment. Some topics on which I spent significant efforts are described here only in overview (in particular the details of the CDMS II analysis, which has been laid out many times before), and some topics which are not described elsewhere are given a somewhat deeper treatment. In particular, this thesis is hopefully a good reference for those interested in the annual modulation limits placed on the low-energy portion of the CDMS II exposure, the design of the detectors for SuperCDMS Soudan, and an overview of the extremely informative data these detectors produce.It is an exciting time. The technology I've had the honor to work on the past few years provides a wealth of information about each event, more so than any other direct detection experiment, and we are still learning how to optimally use all this information. Initial tests from the surface and now underground suggest this technology has the background rejection abilities necessary for a planned 200kg experiment or even ton-scale experiment, putting us on the threshold of probing parameter space orders of magnitude from where the field currently stands.

Superconducting Detectors for Superlight Dark Matter

“…(Other techniques, such as the use of superfluid helium [16], hold promise as well.) The remainder of this letter focuses on the reach of such an experiment into the parameter space of light dark matter.…”

Nuclear-recoil energy scale in CDMS II silicon dark-matter detectors

“…The remainder of the recoil energy is deposited directly into the phonon system as primary phonons. These high-frequency phonons undergo isotopic scattering and cannot travel far from their production sites before down-converting via anharmonic decay [16] into lower-frequency phonons with larger mean free paths, comparable to the thickness of the detector [17]. The lowerfrequency ballistic phonons then interact with either the phonon sensors or un-instrumented material at the detector surfaces.…”

Cryogenic Dark Matter Search detector fabrication process and recent improvements

“…Figure from[19]. Right) Simulation of iZIP internal field lines, showing strong tangential electric fields at the surface and a uniform drift field in the detector bulk, a method proven to discriminate against the previously problematic surface events.Figure from[21].…”