UNC Physics Colloquium

John F. Wilkerson, UNC/TUNL/ORNL

“The elusive lightness of neutrinos”

Neutrinos, enigmatic fundamental particles, were long assumed to be massless until a series of revolutionary experiments over the past two decades revealed that they actually exhibit complex behavior and must possess non-zero mass. From these and other recent measurements we know that neutrinos have minuscule masses, at least 500,000 times lighter than the electron. Yet we still do not know the neutrino’s actual mass nor why it is so light. Determining this absolute neutrino-mass scale is vital to our understanding of fundamental interactions, cosmology, astrophysics and ultimately to answering the underlying question on the origin of particle masses. This talk will review our current understanding of neutrinos and then address the question of how one “weighs” a neutrino? The techniques and latest results from cosmology, double beta decay and direct kinematical methods will be presented, with a focus on the Karlsruhe Tritium Neutrino experiment (KATRIN), which today (Feb. 14) published a new limit, reaching for the first time sub-eV sensitivity from a direct neutrino mass experiment.