From neutrons to neutrinos: On the trail of solar fusion and terrestrial fission

In December 2002, the Japan-based Kamioka Liquid scintillator Anti Neutrino Detector (KamLAND) collaboration announced that its measured rate of antineutrino fluxes from fission reactions in nuclear reactors was smaller than theoretically expected. In September 2003, The Canada-based Sudbury Neutrino Observatory (SNO) collaboration released its latest data on neutrinos from the sun. They conclude, consistent with their earlier measurement, that the measured solar neutrino flux agrees with that expected from fusion reactions in the sun, calculated using standard solar models. Their data also indicate that neutrinos oscillate on their way from the sun to the earth. Indeed, both the observed KamLAND deficit and the SNO measurements are consistent with the idea of neutrino oscillations. Along with earlier experiments, they provide compelling evidence for new physics beyond the Standard Model of particle physics. After briefly describing neutrinos, their sources and their interactions, we will return to the SNO and KamLAND data and explain the extraordinary nature of their results.