Prof. Janet Marie Conrad

The lightest and most elusive of the known matter particles are neutrinos. Their number far exceeds the atoms in the universe. Yet we know surprisingly little about these articles. It is only within the last decade, for example, that we came to realize these particles have mass, albeit very tiny. This became clear when neutrinos were shown to live a double life, transforming from one type into another through the quantum mechanical effect of neutrino oscillations, an effect that requires neutrino mass.

While their masses may be small, the impact of neutrinos on particle physics is enormous. In the Standard Model, which describes particle interactions, neutrinos are massless. So the discovery of mass challenges us to rethink our theory. It also provokes us to ask: “What other properties of neutrinos might be outside of the Standard Model?”

Janet Conrad’s research uses neutrinos as tools to probe for new physics. Until 2007, she was co-spokesperson of the MiniBooNE experiment, which searched for a new neutrino beyond the three types known in the Standard Model. This was motivated by an oscillation result from the Liquid Scintillator Neutrino Detector (LSND) experiment at Los Alamos, which indicated an oscillation wavelength inconsistent with other experiments, perhaps pointing to the existence of a fourth neutrino species. Mini-BooNE provided a strict test of this hypothesis, and ruled out the explanation of a fourth type of neutrino.

However, while one neutrino anomaly has been resolved, another has sprung up. At low neutrino energy, MiniBooNE saw an excess of events above the Standard Model expectation and inconsistent with neutrino oscillations. Its source remains a mystery, which is best explored through a more sensitive detector. To this end, Conrad is involved in the MicroBooNE experiment, which is developing a state-of-the-art detector that makes use of liquid Argon.

At the same time, Conrad has shifted her focus to exploring the properties of the three Standard Model species. While many combinations of oscillations between neutrinos have been observed, there is one which is yet to be seen. The purpose of the Double Chooz experiment, on which Conrad collaborates, is to observe, for the first time, this rare transmutation.