Experimental searches for neutrinoless double-beta decay, direct and indirect WIMP dark matter searches, underground and low-background experiments. Member of the Majorana and LEGEND neutrinoless double-beta decay collaborations. Member of the ABRACADABRA dark matter axion search collaboration
|2018—present||University of North Carolina – Chapel Hill||Professor|
|2013—2017||University of North Carolina – Chapel Hill||Associate Professor|
|2007—2012||University of North Carolina – Chapel Hill||Assistant Professor|
|2003—2006||Lawrence Berkeley National Laboratory||Postdoctoral Fellow|
|1998—2003||Massachusetts Institute of Technology||Graduate Research Assistant|
|Summer, 1997||Geophysical Fluid Dynamics Laboratory||Research Assistant|
|Summer, 1996||High Altitude Observatory, NCAR||Research Assistant|
|1994—1998||University of Denver||Undergraduate Research Assistant|
A long version of my CV and publication list can be found here.
My research is focused on finding experimental answers to some of the most fundamental questions about the nature of matter. Over the past few decades physicists have developed and experimentally confirmed to high precision the so-called "Standard Model" of particle interactions. Although this model is extraordinarily succesful, we know that it has to be incomplete. Three of the major issues that it does not address are the following:
I am a member of the Experimental Nuclear and Particle Astrophysics (ENAP) group at UNC. I also work at the Triangle Universities Nuclear Laboratory (TUNL).
Neutrinoless double-beta decay (NDBD) is a hypothetical nuclear decay associated with the emission of two electrons and no neutrinos from an atomic nucleus. The discovery of this currently unobserved decay would have the following significant implications:
Schematic of the MAJORANA DEMONSTRATOR
Installation of HPGE Detectors in MAJORANA
I'm also a member of the LEGEND collaboration. We are funded to deploy a 200-kg array of enriched HPGe detectors underground at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. We are are also pursuing funding for a tonne-scale version of LEGEND. I'm particularly interested physics other than NDBD that can be done with these experiments, such as searches for dark matter.
The nature of dark matter (DM) remains one of the universe's greatest mysteries. As the gravitational evidence for DM continues to accumulate, the lack of laboratory evidence for DM becomes ever more acute. Axions belong to a broad class of well-motivated dark matter models consisting of light pseudoscalar particles coupled weakly to ordinary matter. The most famous example is the QCD axion, a consequence of the Peccei-Quinn (PQ) mechanism originally proposed to solve the strong-CP problem: the neutron electric dipole moment (EDM) is much smaller than dimensional analysis would suggest, suggesting a fine-tuning of parameters. In the PQ model, the axion couples to the strong nuclear force (quantum chromodynamics, or QCD) so that the lowest-energy field configuration is one where the neutron EDM vanishes. The QCD axion also acquires a small mass that is proportional to its couplings to ordinary matter. The axion is an economical and elegant solution to two seemingly unrelated problems, the nature of DM and the smallness of the neutron EDM.
Rendering and picture of ABRA-10cm prototype.
ABRACADABRA (A Broadband/Resonant Approach to Cosmic Axion Detection with an Amplifying B-field Ring Apparatus) is a new search for sub ueV axions and axion-like particles. It relies on a novel toroidal magnet design in which the axion dark matter would couple to the magnetic field and induce a very small oscillating magnetic field in the center of the torus. This field can be detected using SQUIDs or other quantum sensors. We published our first results in 2018 and developing proposals for the next phases
At UNC and TUNL I have worked on measurements of neutron scattering differential cross-sections in neon and argon. These are germane to dark matter experiments and LEGEND. I have also worked on searching for symmetry violating effects in ortho-positronium decays. Prior to arriving at UNC I was involved with the Sudbury Neutrino Observatory and the Alpha Magnetic Spectrometer (AMS) experiments.
I have taught courses from the introductory to advanced graduate level. From 2012-2015 I led an effort to integrate a significant modern physics component into our introductory physics sequence and to convert it from a traditional lecture/lab/recitation format to lecture-studio . In 2018 I received the university's J. Carlyle Sitterson Award for Teaching First-Year Students.
My course materials are available on Sakai.
A list of student researchers that have worked or are working with me can be found in my CV.