The Ghost Particle
Neutrinos, being considered as one of the fundamental particles, have a very important role in both of the microscopic view of particle physics and the macroscopic view of evolution of the Universe. There are breakthroughs in recent years, the discovery of non-zero neutrinos masses, ‘Neutrino oscillation’ phenomenon or neutrinos mixing. Neutrino Physics has been a hot research topic of High Energy Physics, Astrophysics and Cosmology.
Neutrino Oscillation is being investigated in details in order to understand neutrinos properties such as their masses. Basically speaking, neutrino oscillation can be described by 6 independent parameters, in which 4 of them have been measured with solar, atmospheric, reactor and accelerator neutrinos. While the last two parameters, which are more difficult to measure precisely but physically more meaningful, CP violation phase dcp and mixing angle θ13 become the main targets of next generation of neutrino experiments. On the other hand, the value of θ13 affects the measurement of δcp, and this is why measuring θ13 accurately has become one of the most important experiments about neutrinos.
There are several reasons for using reactor antineutrinos to measure the last mixing angle. First of all, reactors emit huge amount of anti-neutrinos from nuclear reactions. The anti-neutrino flux is much greater than that from the Sun and the atmosphere by many orders of magnitude. Moreover, we have very good understanding about the nuclear reactions taking place inside the nuclear reactors such that we can estimate the anti-neutrino flux with confidence. And the relative amount of resources, such as money and time, needed to build a detector is less than the other kinds of experiments. Finally, the results from a reactor neutrino experiment, which has special physical meaning to understand neutrino matter effect, CP violation and neutrino mass hierarchy, can be a great complement to a long baseline neutrino oscillation experiment. Also, a non-zero δcp measurement may help to explain the asymmetry of matter and anti-matter in the Universe.
Since eighties in the last century, different reactor neutrino experiments have been performed to measure those six parameters. Distances from reactors to detectors range from several meters to hundreds of kilometers. However, because of different experimental difficulties, only the larger mixing angle θ12 and θ23 have been measured. To measure θ13 with high precision, high thermal power of nuclear reactors, suitable mountain profile around the reactors and special neutrino detectors are needed. Daya Bay Nuclear Power Plant can provide the necessary conditions for a θ13 neutrino experiment such that minimum systematic errors can be achieved.