Vulcan08, 26-31May 2008 Barbara Caccianiga, INFN Milano The first real time detection of 7 Be solar neutrinos in Borexino Barbara Caccianiga INFN Milano (an update after 192 days ) see also arXiV: v1 Vulcan08, 26-31May 2008 Barbara Caccianiga, INFN Milano On behalf of the Borexino Collaboration Kurchatov Institute (Russia) Dubna JINR (Russia) Heidelberg (Germany) Munich (Germany) Jagiellonian U. Cracow (Poland) Perugia Genova APC Paris Milano Princeton University Virginia Tech. University Italy USA France Russia Polland Germany SNO, SuperK Solar neutrinos The first idea of Borexino dates back to the 90s, to perform a direct measurement of solar neutrinos below 1 MeV; It took ~ 15 years for it to become reality, due to its technological challenge; Still valid: until now no experiments had probed (in real-time) oscillations below 1 MeV; The Sun shines neutrinos L (neutrinos) ~ 7 Watts = 4 Mev/sec; On earth (~ 6x neutrinos/cm 2 s -1 ) We now know that solar e oscillates during their path from Sun to Earth; The oscillations are matter enhanced through the MSW mechanism; LMA (Large Mixing Angle) m 2 = 7.6 x eV 2 sen 2 =0.87 Borexino down to 200 keV Vulcan08, 26-31May 2008 Barbara Caccianiga, INFN Milano Borexino Borexino is located under the Gran sasso mountain which provides a shield against cosmic rays (residual flux = 1 /m 2 hour); Core of the detector: 300 tons of liquid scintillator contained in a nylon vessel of 4.25 m radius (PC+PPO); 1 st shield: 1000 tons of ultra-pure buffer liquid (pure PC) contained in a stainless steel sphere of 7 m radius; 2 nd shield: 2000 tons of ultra-pure water contained in a cylindrical dome; 2214 photomultiplier tubes pointing towards the center to view the light emitted by the scintillator; 200 PMTs mounted on the SSS pointing outwards to detect light emitted in the water by muons crossing the detector; Only the innermost 100tons of scintillator (R