Dr. Ryan MacLellan, University of Kentucky

Title: 

What will be the next surprise from neutrinos

Abstract:
Neutrinos are the last remaining pieces of the Standard Model of Particle Physics with unknown mass. The fact that they have mass at all has been the only new physics discovered in the Standard Model in generations. Although we do not know the scale of neutrino mass, there is strong evidence that it is sufficiently small that measuring it will be even more challenging than its discovery. The smallness of their mass begs the question: do neutrinos acquire mass via the same mechanism as all of the other, charged, elementary fermions? Neutrinos, being neutral fermions, are the only particles that can be Majorana fermions, which might naturally explain not only the smallness of their mass, but also help explain why the Universe is dominated by matter.

Neutrinoless double-beta decay provides both an "intense" source of potentially Majorana neutrinos and a likely non-negligible capacity to detect them. The process probes baryon-number minus lepton-number conservation, the Majorana nature of neutrinos, and possibly the origin of neutrino masses. However, interesting lifetimes to probe already exceed 10^26 yr.  I will describe the nEXO experiment, a 5-tonne enriched Xenon experiment with sensitivity extending beyond 10^28 yr, or >100 times the current state of the art, as the project I have dedicated my research efforts to over the past 12-1 yr. Since the nEXO project has been indefinitely suspended by DOE, I will also introduce a novel program for the direct measurement of the neutrino mass scale using Cyclotron Radiation Emission Spectroscopy. The project is called Project 8. Dr. Crawford and I hope our Department will contribute to Project 8 over the next decade or more, and eventually, to a measurement of the neutrino mass scale.