A detector of solar neutrinos will be constructed for the purpose of measuring the flux of neutrinos from the decay of beryllium-7 in the solar interior. This decay rate is central to understanding the reactions thought to power the sun. The detector is based on the use of approximately 100 tons of liquid scintillator to detect recoil electrons following neutrino-electron interaction in the detector volume. A large array of photomultiplier tubes will sense the light produced in the liquid scintillator by the recoil electron. Because of the very low rate of events, great attention will be paid to reducing backgrounds from cosmic rays and naturally occurring radioisotopes in the detector proper and the surrounding material. In order to reduce cosmic ray backgrounds, the detector will be located underground. The site chosen is the Gran Sasso underground tunnel in Italy. Construction of this detector, known as Borexino, is an international project involving Italy, Germany, and the US. Results from this experiment will test the standard solar model and help place constraints on the mass of the neutrino. These topics are of great current scientific interest because of earlier results which hint at a substantial reduction in the solar neutrino flux due to neutrino mass and oscillations which are thought to take place in the sun whereby neutrinos change from one so-called flavor into another, i.e. from an electron neutrino into a muon or tau neutrino. The joint NSF/DOE Nuclear Science Advisory Committee highlighted this science in its 1996 Long Range Plan. Education of students and postdocs is a strong component of this experimental program.
This project is jointly supported by the Division of Physics, Division of Astronomy and the MPS Office of Multidisciplinary Activities. ***
