Neutrinos and the hunt for the last mixing angle

Neutrinos are the universe's second most common particles after photons. During their journey through space-time, the elusive neutrinos can change types through the phenomenon called neutrino oscillations. The hunt for the Θ13 mixing angle has mainly been taken up by 3 neutrino experiments: the Daya Bay experiment in China, the Double Chooz experiment in France and the RENO experiment in South-Korea. All 3 are reactor neutrino experiments, which examine electron antineutrinos from nuclear power plants to directly determine the value of Θ13. We have now 3 independent measurements from 3 different experiments which all indicate that the value of the mixing angle Θ13 is about 9 degrees. One of the 3 CP-violating phases, the so-called Dirac CP-violating phase δ, can be measured using neutrino oscillation experiments. This phase appears only in combination with the third mixing angle Θ13. Thus a non-zero value of Θ13 means that it is, in principle, possible to determine δ. Accelerator-based neutrino oscillation experiments will provide the most promising opportunity to observe CP violations by studying both neutrino and anti-neutrino oscillations. If anti-neutrinos do not oscillate in the same way as neutrino do, then this will be a signal of CP violation. The fact that neutrinos are massive and mixed means that the Standard Model must be modified to include massive and mixed neutrinos. (A.C.)