Search for Electron Antineutrinos From The Sun With KamLAND Detector

In this dissertation I present the results of the search for the electron antineutrinos from the Sun with Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND). There is no known direct production of the electron antineutrinos in the Sun. However, in the some theoretical models with the large neutrino magnetic moment antineutrinos from the Sun can be produced e.g. via Spin Flavor Precession mechanism (SFP). Search for solar antineutrinos potentially can provide new information about fundamental properties of neutrinos. The most sensitive one-kiloton antineutrino detector KamLAND gives the possibility to search for such antineutrinos.

The analysis described in this dissertation is based on 1425.9 days of data collection in KamLAND. The search for the electron antineutrinos have been made within 8.8-16.3MeV antineutrino energy range, that is above energies of reactor antineutrinos and where properties of the solar B⁸ neutrinos are well studied. Based on the number of observed candidates and estimated background rates the upper limit on the electron antineutrino flux is set to be less than 1.2×10² cm^-2s^-1 at 95% confidence level. The upper limit on the probability of conversion electron neutrinos produced in the Sun to electron antineutrinos is found to be less than 9.8×10^-5 at 95% confidence level. Using the conversion probability the upper limit on the product of the neutrino magnetic moment and the transverse component of the magnetic field in the core of the Sun is set to be 7.7×10^-2. The same limit can be used on the diffuse Supernovae neutrino flux. The estimated background rates can make significant impact on the design of the future neutrino scintillator detectors.