calor02 pasadena (usa) 25-29 march 2002
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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1Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
Borexino: A Real Time Liquid Scintillator Detector for Low Energy Solar Neutrino StudyLino Miramonti
Milan University & I.N.F.N
(7Be)) = 862 keV
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2Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
LaboratoriNazionaliGran Sasso
~ 3500 meters water equivalent
Borexino
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3Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
The Borexino conceptual design
ν are detected via the:
),,( exee xx
The signature of the ν event is the scintillation light produced by the recoil e-
The signature of the ν event is the scintillation light produced by the recoil e-
σ(νe) 5σ(νμ,τ)
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4Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
eLieBe 77
),,( exee xx
Eν = 862 keV (monochromatic)ΦSSM = 4.8 · 109 ν s-1 cm2
σ 10-44 cm2 (@ 1 MeV)
Recoil electron energy
νe
νx
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5Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
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6
Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
The Scintillator
300 tons of liquid scintillatorPC + PPO (1,5 g/l)
= 0.88 g cm-3 n = 1.505
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
alphagamma/beta
Normalized emission spectra of pseudocumene (PC) and of the scintillator mixture (PC+PPO 1.5 g/l)
Time decay distribution of the scintillator for emission excited by α or β-γ radiation
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
Energy Resolution: FWHM 12% @ 1 MeVTime Resolution: 10 cm @ 1 MeV
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7Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
Inner Vessel
Outer Vessel
PMTs on the Stainless Steel Sphere
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8Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
forΦν= 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 PMTsRadioactivity from the rockMuon induced background
Material U & Th content
Scintillator 10-16 g/g
Nylon Vessel 10-12 g/g
PC buffer 10-14 g/g
Water buffer 10-10 g/g
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 FacilityCounting Test Facility (Borexino prototype) in 1997
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9Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
Borexino expected performancesIn 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)
Oscillation
frame
Events/day (in 100 t, 250-800 keV)
SMA ~ 12
LMA ~ 31
LOW ~ 29
Vaccum ~ 23
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10Calor02 Pasadena (USA) 25-29 March 2002 Lino Miramonti - University and INFN Milano
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.
• 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.