Low Energy Neutrino Physics After SNO and KamLAND

In the recent years important discoveries in the field of low energy neutrino physics (Eν in the ≈ MeV range) have been achieved. Results of the solar neutrino experiment SNO show clearly flavor transitions from νe to νμ,τ . In addition, the long standing solar neutrino problem is basically solved. With KamLAND, an experiment measuring neutrinos emitted from nuclear reactors at large distances, evidence for neutrino oscillations has been found. The values for the oscillation parameters, amplitude and phase, have been restricted. In this paper the potential of future projects in low energy neutrino physics is discussed. This encompasses future solar and reactor experiments as well as the direct search for neutrino masses. Finally the potential of a large liquid scintillator detector in an underground laboratory for supernova neutrino detection, solar neutrino detection, and the search for proton decay p → Kν is discussed. 1 Situation after SNO and KamLAND In SNO (Sudbury Neutrino Observatory) the flavor transition of solar neutrinos from νe into the νμ or into the ντ state has been clearly demonstrated[1]. About 2/3 of the solar B-neutrinos above ≈ 5 MeV energy transform into the other flavor on their way from the solar center to the Earth. The total measured flux of solar B-neutrinos however is in agreement with theoretical expectations. Hence, the long standing solar neutrino problem is basically solved. We know, that the pp-cycle is the main energy source of the sun and the experimental uncertainty on the B-flux is already below the theoretical one. In KamLAND the disappearance of ν̄e, emitted by nuclear power reactors at distances of several hundreds of kilometers has been observed[2]. This can be interpreted as evidence for neutrino oscillations, which are a direct consequence of neutrino masses and neutrino mixing. The weak interaction eigenstates να (α = e, μ, τ) can be expressed as linear combinations of mass eigenstates νi (i = 1, 2, 3)