The Parno Group

My group's research focuses on neutrinos, which are fundamental particles that are shrouded in mystery. We don't know their mass; we don't know whether they violate CP symmetry; we don't even know whether they're their own antiparticles. All that makes them rather interesting! We are currently involved in several experiments to try to understand more about them.

Neutrino Mass Since the late 1990s, we've known that neutrinos have mass, but the actual mass scale has proven remarkably difficult to pin down -- despite being of critical importance for particle theory and for the evolution of the early universe. Our group is involved in two different experiments that aim for a direct, model-independent measurement of the neutrino-mass scale via the kinematics of tritium beta decay. In a nutshell, if you make an extremely precise determination of the extreme high-energy tail of the beta spectrum from this decay, you can observe a characteristic shape distortion due to the neutrino mass -- which is energy that the beta electron cannot carry away from the decay.

I have been the U.S. Spokesperson for the KATRIN experiment since 2022. This experiment, which began running in 2019, has achieved the world's leading kinematic sensitivity to the neutrino-mass scale. Detailed analysis of the full data set is in progress, as well as R&D work toward future measurement phases that will expand KATRIN's sensitivity to beyond-standard-model effects. Over the years, my group and I have worked on the focal-plane detector; on backgrounds in the main-spectrometer; on ion transport in the beamline; on activity from tritium adsorbed on surfaces in the experiment; and on the final-state distribution resulting from decay of tritium that is bound in molecules. We have addressed that last problem partly through the design, construction, and analysis of the TRIMS molecular-physics experiment, along with colleagues from the University of Washington.

More recently, we have joined the Project 8 experiment, which aims for a tritium-based neutrino-mass measurement using an entirely different technology: measurement of cyclotron radiation from individual beta electrons trapped in a magnetic field. In this R&D collaboration, my group has worked on magnetic-field design and on modeling spectral response.

Our neutrino-mass efforts have been supported by the United States Department of Energy, Office of Science (Nuclear Physics, Fundamental Symmetries and Neutrinos) through Award DE-SC0019304, as well as through alumni gifts.

Neutrino Scattering We are part of the COHERENT experiment to study interactions of relatively low-energy neutrinos (less than about 50~MeV) with nuclei. Our neutrinos come from Oak Ridge National Laboratory's, Spallation Neutron Source, which produces copious neutrinos from pion and muon decay at rest in addition to the neutrons that are its main reason for existence. The pulsed time structure of the beam is tremendously helpful for controlling backgrounds.

COHERENT has measured coherent elastic neutrino-nucleus scattering (CEvNS) in multiple nuclei; studied several charged-current interactions that are relevant for supernova-neutrino detection and for nuclear theory; and searched for accelerator-produced dark matter. Our group has done significant work on understanding neutron backgrounds and on simulating the neutrino flux. The 10\% uncertainty on that latter figure has motivated the construction of a water Cherenkov detector to benchmark the neutrino flux; our group had primary responsibility for building the second module of that detector.

Our COHERENT efforts have been supported by the United States Department of Energy, Office of Science (High-Energy Physics, Intensity Frontier), through an Early Career Award (DE-SC0022125) and through Award DE-SC0010118, as well as through alumni gifts.