“BOREXino” refers to an experiment performed by an international collaboration centered on solar neutrino physics.
Neutrinos are released in radioactive beta-decays, like what happens in the sun during nuclear fusion. Given the enormity of the sun, this would correspond to a flux of about 6.5 x 1010 neutrinos per square centimeter per second hitting the earth. However, neutrinos are notoriously difficult to detect and measure. Early experiments calculated far less (about 40%) neutrinos than predicted actually hitting the earth, and did not find significant variations with either day/night or season.
The Borexino detector, located underground in the Laboratori Naxioli del Gran Sasso in Italy, is a new look at this problem. It is capable of detecting low-energy solar neutrinos in real-time, and is capable of precisely measuring the beryllium solar neutrino flux and its day/night asymmetry – and its ultrapure scintillator (acting as a light concentrator) makes for some really cool pictures.