Neutrino Experiments and Their Implications

Solar neutrino experiments, especially with the announcement of recent results from the Sudbury Neutrino Observatory (SNO) , have reached the precision stage. An analysis of the data from SNO as well as data from other solar neutrino experiments (Super-Kamiokande [SK] , Chlorine , and Gallium ), combined with the data from the reactor experiment KAMLAND , place severe constraints on the neutrino parameters, especially mixing between first and second generations . The neutrino parameter space obtained from such a global analysis, including the neutralcurrent results from the SNO salt phase, is shown in Fig. 1 . The mixing angle between first and second generations of the neutrinos dominates the solar neutrino oscillations whereas the mixing angle between second and third generations dominates the oscillations of atmospheric neutrinos. There are several puzzles in the data. Both mixing angles seem to be close to maximum, very unlike the mixing between quarks. Also the third mixing angle, between first and third generations, seems to be very small, even possibly zero. It is especially important to find out if this mixing angle is indeed different from zero since in the mixing matrix it multiplies a CP-violating phase. Such a CP-violation may have far reaching consequences. To explain the baryon excess (over antibaryons) in the Universe, Sakharov pointed out that it may be sufficient to satisfy three conditions: i) Baryon number non-conservation (which is readily satisfied by the grand unified theories), ii) CP-violation, and iii) Non-equilibrium conditions. It