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Calor02 Pasadena (USA) 25-29 March 2002

Borexino : A Real Time Liquid Scintillator Detector for Low Energy Solar Neutrino Study. Lino Miramonti Milan University & I.N.F.N. E(n (7Be) ) = 862 keV. Calor02 Pasadena (USA) 25-29 March 2002. Lino Miramonti - University and INFN Milano. L aboratori N azionali G ran S asso.

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Calor02 Pasadena (USA) 25-29 March 2002

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  1. Borexino: A Real Time Liquid Scintillator Detector for LowEnergy Solar Neutrino Study Lino Miramonti Milan University & I.N.F.N E(n(7Be)) = 862 keV Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

  2. Laboratori Nazionali Gran Sasso Borexino ~ 3500 meters water equivalent Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

  3. The Borexino conceptual design ν are detected via the: σ(νe)  5σ(νμ,τ) The signature of the νevent is the scintillation light produced by the recoil e- Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

  4. Eν = 862 keV (monochromatic) ΦSSM = 4.8· 109 ν s-1 cm2 νe νx Recoil electron energy σ  10-44 cm2 (@ 1MeV) Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

  5. Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

  6. The Scintillator • Characteristics of the scintillator: • High photon yield (11000 ph/MeV) • Fast response (τ  3.6 ns) • (τ  5.5 ns in large volumes) • Good α/β discrimination • High transparency • Can be purified • λmax 365 nm 300 tons of liquid scintillator PC + PPO (1,5 g/l) r = 0.88 g cm-3 n = 1.505 Energy Resolution: FWHM  12% @ 1 MeV Time Resolution:  10 cm @ 1 MeV alpha gamma/beta • Characteristics of the PMs: • 8” Thorn EMI 9351 • Efficiency = 26 % (@ 420 nm) • Transit time spread σ = 1 ns • Peak/valley = 2.5 • Dark noise = 1 kHz • Gain = 107 Time decay distribution of the scintillator for emission excited by α or β-γ radiation Normalized emission spectra of pseudocumene (PC) and of the scintillator mixture (PC+PPO 1.5 g/l) Lino Miramonti - University and INFN Milano Calor02 Pasadena (USA) 25-29 March 2002

  7. PMTs on the Stainless Steel Sphere Outer Vessel Inner Vessel Lino Miramonti - University and INFN Milano Calor02 Pasadena (USA) 25-29 March 2002

  8. for Φν= 4.8 · 109 cm-2 s-1 σ ~ 10-44 cm2 ~ 55 events per day in 100 tons of fiducial volume! (250 keV – 800 keV) Reducing the background! The background which could give signal in the so called “ν window” (250 keV – 800 keV) can be divided in two main classes: Internal background (scintillator itself) Mainly natural radioactivity External background (coming from outside the IV) Radioactivity from PMTs Radioactivity from the rock Muon induced background • Radiopurity levels obtained by: • For scintillator – water extraction, N2 stripping, distillation and silica gel • For water – reverse osmosis, deionization, N2 bubbling and stripping The capability to reach the requested radiopurity levels has been proved by the Counting Test Facility (Borexino prototype) in 1997 Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

  9. Borexino expected performances In non-oscillation frame Signal ~ 55 events per day (in 100 tons, 250-800 keV ) Bkg ~ 15 events per day (in 100 tons, 250-800 keV) Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

  10. Present status of the detector • The 92% of PMTs are installed. • The PC procurement is in progress. • Water filling: summer-fall 2002. • Borexino will take data (background) during the filling of the detector. • Borexino will take data(physics events) from the spring 2003. Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano

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