Precise Measurement Of Solar Neutrino Oscillation Parameters And Analysis Of Sub-leading Effects

In 1930, Pauli postulated the existence of neutrino in his attempt to explain the apparent violation of energy conservation in beta decay. From then on, this mysterious particle attracted the most attention of physicists. The study of neutrinos had also brought great progress in particle physics.Neutrinos have a very small mass, and they only involve in weak interactions, which make them extremely hard to detect and to study. The first detection of electron anti-neutrinos from reactor was made by Reines and Cowan in the year 1956, almost 26 years after neutrino was postulated. During the next 50 years, with the discovery of muon neutrinos and tau neutrinos, we finally find the whole family of active neutrinos.Now, we know that, the neutrinos have different masses, and they are mixed. So, they may transform into other flavors in their propagation, and this is the so-called neutrino oscillation. After the discovery of the three generations of active neutrinos, we need to detect the neutrino mass spectrum and mixing matrix through various neutrino experiments. That is a fundamental and very important task in particle physics. After that, we will have the opportunity to search for the answers to some more attractive questions, such as the origin of neutrino masses and so on.Solar is one of the most important neutrino sources in nature; it produces a large amount of electron neutrinos, which can be used to study the neutrino mass spectrum and mixing matrix. Homestake was the first experiment to successfully detect and count solar neutrinos. It gave its first results in the year 1968, which raised the famous solar neutrino problem. After that, with the development of different solar neutrino experiments, more detailed information of solar neutrino fluxes was gained. In the year 2001, the SNO experiment made the first measurement of the total flux of active neutrinos from the Sun. The results were consistent with that predicted by the standard solar model. Meanwhile, SNO provided a direct evidence of flavor transformation in solar neutrino propagation. Soon after that, the reactor anti-neutrino experiment KamLAND made the first observation of disappearance of electron anti-neutrinos, which finally confirmed the neutrino oscillation mechanism as the solution to the famous solar neutrino problem.After the resolve of the solar neutrino problem, the study of solar neutrinos turns to the precise measurement of neutrino oscillation parameters, and further more, to searching for possible sub-leading effects in these experiments. In this thesis, we first give a briefly review of the history of solar neutrinos. Then, we introduce the basic contents of neutrinos in particle physics, including the description of neutrinos in the standard model and how to give finite mass to neutrinos. The neutrino oscillation mechanism has been confirmed as the solution to the solar neutrino problem. We give a detailed introduction of the theory of neutrino oscillations and also a detailed description of solar neutrinos propagation in solar interior. With the contents above, we perform a traditional least-squares analysis based on all data sets from KamLAND and solar neutrino experiments, and show the best-fit point and different allowed regions in oscillation parameter space. We find that, the recent data sets have brought stricter constraints on the allowed regions. The data from SNO salt phase and NCD phase have improved the precision inθ1 2 detection, while the KamLAND data have greatly improved the precision inΔm 122 detection. After a global analysis, solar neutrino oscillation parameters are determined with a very high precision.Further more, we find a discrepancy between the KamLAND and solar neutrino results when their data are analysed separately. This may be an indication of sub-leading effects that exist in the solar neutrino experiments. We introduce the possible source of sub-leading effects, and study the dependence of theoretical prediction on solar and earth models as the preparation. Then, we simulate the future experiment results using Monte-Carlo method and discuss the ability of different experiments in searching for the sub-leading effects. As an example, we choose the non-zeroθ1 3 as a possible source of sub-leading effects and investigate its impact on data analysis. We find that, the discrepancy between the KamLAND and solar neutrino results can be reduced by choosing an appropriate small value for the mixing angleθ1 3. This fact gives a hint of the non-zero value ofθ1 3. After that, we perform an analysis in three-flavor oscillation framework and find a non-zero value ofθ1 3 at 1σconfidence level, which is an interesting result.The data from KamLAND and solar neutrino experiments cannot give a strict constraint on the allowed range ofθ1 3. Precise measurement ofθ1 3 is an important goal in the next generation neutrino oscillation experiments. The BAYA-Bay reactor neutrino experiment located in southern China will play an important role inθ1 3 detection. We simulate the possible results of the BAYA-Bay experiment with different arrangements of the detectors'positions and different data analysis methods to show its ability to detect the small mixing angleθ1 3. In our simulation, the experiment will be able to discover a non-zero sin 2 2θ1 3 if it is greater than 0.02. After the precise measurement ofθ1 3 in future, we will have the opportunity to detect the CP violation phase, which is an important factor in the study of flavor physics.Neutrino physics is a young and active topic; it has brought great progress in particle physics. Neutrinos have also profound implications to astrophysics and cosmology; e.g. the massive neutrinos have significant effects on the formation of the universe structure, the possible CP violation in neutrino oscillations could account for the matter-antimatter asymmetry in current universe, and so on. With the operation of the next generation neutrino experiments, we will get more and more information about neutrino mass,neutrino mixing and some other physical properties of neutrinos. We can anticipate that, those interesting questions that related to neutrinos will be solved in the near future.