Results from the Borexino experiment Results from the Borexino - PowerPoint PPT Presentation

Results from the Borexino experiment Results from the Borexino experiment Timo Lewke Timo Lewke Technische Universität München Technische Universität München On behalf of the Borexino Collaboration On behalf of the Borexino Collaboration Rencontres de Moriond – 7- 14 March 2009 – La Thuile Rencontres de Moriond – 7- 14 March 2009 – La Thuile

The Experimental Site The Experimental Site Borexino is located in the LNGS Borexino is located in the LNGS Underground Laboratory in the Underground Laboratory in the mountains of Abruzzo, Italy. mountains of Abruzzo, Italy. Shielding provided by 1400m m of rock: of rock: Shielding provided by 1400 ~3800 m.w.e ~3800 m.w.e

The Borexino Detector The Borexino Detector Stainless Steel Sphere: Stainless Steel Sphere: 2212 PMTs 2212 PMTs Scintillator: Scintillator: 1350m³ 1350m³ 270t PC+PPO 270t PC+PPO r=6.85m r=6.85m Water Tank: Water Tank: 208 PMTs 208 PMTs Nylon Vessel: Nylon Vessel: 2100m³ 2100m³ Inner : 4.25m Inner : 4.25m r=9m r=9m Outer: 5.50m Outer: 5.50m Carbon Steel Plates Carbon Steel Plates

Expected Spectrum in Borexino Expected Spectrum in Borexino Neutrino detection principle: Electron scattering Neutrino detection principle: Electron scattering + e - -> + e - First real-time measurement down to 200keV. First real-time measurement down to 200keV. First simultaneous measurement of solar First simultaneous measurement of solar neutrinos from vacuum dominated and neutrinos from vacuum dominated and matter-enhanced oscillation regions. matter-enhanced oscillation regions. Expected rates: Expected rates: ⁷ Be ⁷ Be : : ~ 50 c/d/100t ~ 50 c/d/100t ⁸ B ⁸ B : ~0.3 c/d/100t : ~0.3 c/d/100t pp Neutrino spectrum Borexino threshold Borexino threshold ⁷ Be Low threshold of 200keV because Low threshold of 200keV because pep of high radioactive purity: CNO of high radioactive purity: ⁸ ⁷ ⁸ ⁷ ²³ U 1.6· ·10 10¯ ¯¹ g/g ¹ g/g ²³ U 1.6 ⁸ ⁸ ²³²Th 6.8· ·10 10¯¹ g/g ¯¹ g/g ²³²Th 6.8 ⁸ B Electron recoil spectrum

⁷ Be Solar Neutrino Flux ⁷ Be Solar Neutrino Flux Spectrum of 192 live days Spectrum of 192 live days Applied cuts: Applied cuts: ● Muons rejected Muons rejected ● 2ms cut after each muon 2ms cut after each muon ● Rn daughters vetoed Rn daughters vetoed ● FV cut FV cut Electron recoil spectrum Measured rate: 49± ±3 3 stat ±4 4 sys c/d/100t Measured rate: 49 stat ± sys c/d/100t Theoretical rate Theoretical rate ● MSW-LMA: MSW-LMA: 48± ±4 c/d/100t 4 c/d/100t 48 ● no oscillation: no oscillation: 75± ±4 c/d/100t 4 c/d/100t 75 ⁷ ⁷ Hypothesis of no oscillation for Be solar Hypothesis of no oscillation for Be solar neutrinos is rejected by the measurement neutrinos is rejected by the measurement  . at 4  . at 4 Electron recoil spectrum

Calculation of the pp & CNO Fluxes Calculation of the pp & CNO Fluxes (Combining the Borexino results with other Experiments) (Combining the Borexino results with other Experiments)  i measured R k = ∑ i , k f i = R i , k f i P ee  i predicted i R i , k = expected rate of source i for experiment k at the nominal SSM flux i , k = survival probabilityfor source i abovethe threshold for experiment k P ee k = Homestake,Gallex i = pp,pep,CNO, 7 Be, 8 B f f B = 0.83 = 0.83± ±0.07, measured by SNO and SuperK 0.07, measured by SNO and SuperK ⁸ ⁸ B f f Be = 1.02 = 1.02± ±0.10 given by the Borexino results 0.10 given by the Borexino results ⁷ ⁷ Be  2 Performing a  2 based analysis of all neutrino experiments adding the luminosity constraint: based analysis of all neutrino experiments adding the luminosity constraint: Performing a  ) (1  = 1.005 +0.008 +0.008 f pp ) f pp = 1.005 -0.020 (1 -0.020 f CNO < 3.80 (90% C.L.) f CNO < 3.80 (90% C.L.) This represents the best determination of the pp solar neutrino flux. This represents the best determination of the pp solar neutrino flux.

⁸ B Solar Neutrino Flux ⁸ B Solar Neutrino Flux Spectrum of 246 live days measurement. Spectrum of 246 live days measurement. raw spectrum Cosmogenic background sources: Cosmogenic background sources: Muons ● Muons after µ-cut Muon induced secondaries ● Muon induced secondaries Muon induced radionuclides ● Muon induced radionuclides after FV after 5s-µ-cut, neutron-cut, Internal background: Internal background: 10 C-cut and 214 Bi-cut Radon emanation from the nylon vessel ● Radon emanation from the nylon vessel ⁰⁸ ⁰⁸ ² Tl contamination of the scintillator ● ² Tl contamination of the scintillator expected 208 Tl spectrum, taking the light quenching into account

⁸ B Solar Neutrino Flux ⁸ B Solar Neutrino Flux no oscillation MSW-LMA ⁸ ⁸ Measured B neurino rate: Measured B neurino rate: 0.26± 0.26 ±0.04 0.04 stat stat ± ±0.02 0.02 sys sys c/d/100t c/d/100t Expected rate (SSM and MSW-LMA): 0.27± ±0.03 0.03 c/d/100t Expected rate (SSM and MSW-LMA): 0.27 c/d/100t  Non-oscillation excluded at 4.2  Non-oscillation excluded at 4.2

Survival Probability Survival Probability MSW-LMA solution ⁷ Be matter enhanced oscillation vacuum oscillation ⁸ B pep ⁷ ⁸ ⁷ ⁸ Assuming the SSM and MSW-LMA solution the measurement of Be and B neutrino rate Assuming the SSM and MSW-LMA solution the measurement of Be and B neutrino rate corresponds to: corresponds to: ⁷ ⁷ P ee ( Be) = 0.56± ±0.10 0.10 P ee ( Be) = 0.56 ⁸ ⁸ P ee P ee ( B) ( B) = 0.35 = 0.35± ±0.10 at the effective energy of 8.6MeV 0.10 at the effective energy of 8.6MeV Measurement is in agreement with the prediction of the MSW-LMA solution for solar neutrinos. Measurement is in agreement with the prediction of the MSW-LMA solution for solar neutrinos.

Summary Summary Achieved so far: Achieved so far: ● First real-time measurement of Be neutrinos ⁷ ⁷ First real-time measurement of Be neutrinos ● First real-time measurement of B neutrinos down to an energy of 2.8MeV using ⁸ ⁸ First real-time measurement of B neutrinos down to an energy of 2.8MeV using a liquid scintillator a liquid scintillator ● First simultaneous measurement of solar neutrinos from vacuum dominated and First simultaneous measurement of solar neutrinos from vacuum dominated and matter-enhanced oscillation regions matter-enhanced oscillation regions ● Current best limits for pp- and CNO-neutrinos Current best limits for pp- and CNO-neutrinos In progress: In progress: ● Direct measurement of pep- and CNO-neutrinos Direct measurement of pep- and CNO-neutrinos ● Source calibration to decrease systematic errors Source calibration to decrease systematic errors In future: In future: ● Measurement of the solar pp-flux Measurement of the solar pp-flux ● Antineutrino observations (geoneutrinos, reactor, from the sun) Antineutrino observations (geoneutrinos, reactor, from the sun) ● Supernova neutrinos and antineutrinos (joining SNEWS during 2009) Supernova neutrinos and antineutrinos (joining SNEWS during 2009)