Review of Neutrino Oscllations Experiments

Abstract

Several experiments have sought evidence for neutrino mass and mixing via the phenomenon of neutrino flavor oscillations. In a three neutrino model, these oscillations are described by three angles, two mass splittings, and one CP violating phase. Experiments using neutrinos from the Sun, the atmosphere, nuclear reactors, and particle accelerators have gathered considerable information on these angles and splittings. Two of the three angles are known to be large: $\theta_{12} \simeq 33^\circ$, $\theta_{23} \simeq 45^\circ$, and an upper limit is known on the third, $\theta_{13}<10^\circ$. Likewise, the mass splittings are known to fall in the range $\Delta m^2_{12} \simeq 8 \times 10^{-5}$ and $|\Delta m^2_{23}| \simeq 2.4 \times 10^{-3}$ eV$^2$. Several questions remain: the sign of the 2--3 mass splitting, the size of the unknown angle $\theta_{13}$, and the size of the CP violating phase are yet to be measured. Also, a report of short-baseline $\bar{\nu}_e \to \bar{\nu}_mu$ oscillations has yet to be confirmed. These open questions are the target of an experimental neutrino oscillation program currently underway. This report will attempt to summarize the current state of neutrino oscillation measurements and the future program in as succinct a manner as possible.