Thomas Wester, Boston University: Neutrino Mass Ordering Analysis using Atmospheric Neutrinos at Super-Kamiokande

Whether our universe contains two light neutrinos and one heavy neutrino, or the other way around, known as the neutrino mass ordering, is an unsolved question. One probe of the neutrino mass ordering is to measure neutrino oscillations in matter using atmospheric neutrinos. Super-Kamiokande (SK) is a 50 kiloton water-Cherenkov detector which has collected over 20 years of atmospheric neutrino data. This talk will present an analysis of SK atmospheric neutrino oscillations, optimized for sensitivity to the neutrino mass ordering. Specifically, I will highlight recent improvements to the analysis methodology and the addition of new data. The atmospheric neutrino data are also analyzed jointly with beam-line neutrino data from the T2K experiment to enhance the sensitivity to the neutrino mass ordering and search for CP violation. The analysis finds that SK and T2K both prefer the normal neutrino mass ordering and maximal CP violation, consistent with each experiment observing excess electron neutrino appearance.