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Thursday, May 16

Neutrino Oscillations: Early Hints of the Mass Hierarchy

Bernadette Kafwimbi Cogswell, Vanderbilt University , Nashville, TN
ORNL Physics Division Seminar
3:00 PM — 4:00 PM, ORNL, Building 6008, Large Conference Room
Contact: Alfredo Galindo-Uribarri (uribarri@ornl.gov), 865.574.6124

Abstract

The only experimentally observed phenomenon that lies outside the standard model is neutrino oscillations: the coherent mixing of propagating neutrino mass eigenstates that leads to neutrino flavor conversion in the lab. A current goal in the field is to determine the values of the mixing angles and mass splittings that characterize this mixing. However, a related open question is the hierarchy question, which mass state is lightest and which heaviest? We point out a broken symmetry in the oscillation probability relevant to this question. For the recently measured, surprisingly large, value of the mixing angle theta-13, we find that this broken symmetry lifts a four-fold degeneracy. This symmetry breaking effect proves very meaningful for the hierarchy question: in the global data, it leads to a preference for the inverse hierarchy at the 97.2% level.