BOREXINO

Home page of the Experiment: http://borex.mi.infn.it/

Borexino is a detector of 300 tons of liquid scintillator, and the solar neutrinos are detected via the electroweak elastic scattering on electrons of scintillator; the recoil electron spectrum will have a maximum of 664 keV kinetic energy.The detection threshold for observing such process will be of 250 keV, so that a rate of about 50 events/day is predicted by the Standard Solar Models in the 100 tons Borexino fiducial volume.

The feasibility of this program depends critically on the expected background in the 250/700 keV energy window. This background was extensively studied with the CTF detector.

The 7Be neutrino line is predicted by all standard solar models to be the second most important neutrino production reaction (after the basic pp reaction) in the sun. The flux of 7Be neutrinos is predicted much more accurately (uncertainty less than 10%) and is about a 1000 times larger than the 8B neutrino flux that is measured by SuperKamiokande and SNO. Also, since 7Be decay produces only neutrino lines, the theoretical predictions of neutrino oscillations are more unique for 7Be than for the 8B neutrinos, which have a broad energy spectrum (0-15 MeV).

From the data of the solar neutrino experiments operating so far, the 7Be rate is estimated to be much lower than the prediction of the Standard Solar Model. The expected rate in LMA solution is 0.65/SSM.

In summary, the solar 7Be neutrino line intensity and its time (seasonal, day-night) variations will be the main goal of the Borexino experimental program. In some aspects of the study of the time variations, Borexino is unique both for MSW and Vacuum scenarios.

In addition to 7Be neutrino physics, other goals under study by the collaboration (potential Borexino goals) are:

- More solar neutrino studies: 8B and CNO studies.

- Neutrino magnetic moment can be studied using a 51Cr source. An indicative sensitivity of 10-11 Bohr magnetons is expected.

- Antineutrino searches can be performed through the Reines-Cowan detection reaction. This can be used to search for neutrino/antineutrino transitions in the case of solar neutrinos or to a measurement of the Earth emitted neutrinos.