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Borexino and Solar neutrinos

Borexino and Solar neutrinos. Igor Machulin RRC “Kurchatov Institute ” On behalf of the Borexino Collaboration. Milano. Perugia. Borexino collaboration. Genova. Princeton University. APC Paris. Virginia Tech. University. Munich (Germany). Dubna JINR (Russia). Kurchatov Institute

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Borexino and Solar neutrinos

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  1. Borexino and Solar neutrinos Igor Machulin RRC “Kurchatov Institute” On behalf of the Borexino Collaboration

  2. Milano Perugia Borexino collaboration Genova Princeton University APC Paris Virginia Tech. University Munich (Germany) Dubna JINR (Russia) Kurchatov Institute (Russia) Jagiellonian U. Cracow (Poland) Heidelberg (Germany) St.-Petersburg INF (Russia)

  3. Solar neutrinos from nuclear reactions in the Sun core, dominant pp cycle. 8B 8Be*+ e+ +e 2 99,77% p + p  d+ e+ + e 0,23% p + e - + p d + e 84,7% ~210-5 % d + p 3He + 13,8% 3He + 4He 7Be +  13,78% 0,02% 7Be + e-7Li + e 7Be + p 8B +  3He+3He+2p 7Li + p ->+ 3He+p+e++e Igor Machulin , RRC “Kurchatov Institute “

  4. Solar neutrinos from nuclear reactions in the Sun core, sub-dominant CNO cycle nfrom CNO cycle had not yet been observed LCNO / Lsun < 5-6% (GALLEX/GNO+SAGE) …dominates in stars with more mass than our sun… =>Large astrophysical relevance Igor Machulin , RRC “Kurchatov Institute “

  5. Solar neutrino spectrum according to the SSM (Bahcall-Serenelli 2005) Borexino energy range for Solar neutrino measurements in Real-time Igor Machulin , RRC “Kurchatov Institute “

  6. Oscillations and matter effects Oscillation length ~ 102 km => oscillation smeared out and non-coherent Effective ne mass (due to forward scattering on electrons) is enhanced by a potential A A ~ GFNeE2 => for E > 1 MeV matter effect dominates and leads to an enhanced ne suppression for those energies… MSW Effect in Sun Missing info here before BOREXINO Now additional Improvement on uncertainty on pp-ne flux 1 10 MeV Vaccum regime Matter regime

  7. Experimental site for Borexino - Gran Sasso Laboratory Laboratori Nazionali del Gran Sasso near L’Aquila, INFN. Underground Lab provides shielding from cosmic background of 3500 m water equivalent Igor Machulin , RRC “Kurchatov Institute “

  8. Borexino Detector Design Stainless Steel Sphere: 2212 photomultipliers 1350 m3 Scintillator: 278 t PC+PPO (1,5 g/l) in 150 mm thick nylon vessel Buffer : 890 t PC+DMP(5 g/l) 2 Nylon vessels: Inner: 4.25 m Outer: 5.50 m Water Tank: g and n shield • water Čherenkov • detector 208 PMTs in water 2100 m3 20 legs BOREXINO Design is based on the principles of graded shielding Igor Machulin , RRC “Kurchatov Institute “

  9. PhotoMultiplierTube -PMT Nylon vessel installation Installation of PMTs on the sphere Igor Machulin , RRC “Kurchatov Institute “

  10. Detector filling completed and data taking started- May 15th, 2007 Igor Machulin , RRC “Kurchatov Institute “

  11. Monochromatic n En=862 KeV FSSM=4.8x109n/ (s*cm2) BorexinoPhysics • Be-7 neutrino detection in real time mode • pep, CNO and pp neutrino detection • B-8 neutrino detection • Measurement of neutrino magnetic moment • with the sensitivity of few* 10-11mB level • Geo and reactor antineutrinos • Supernova detection • Rare processes studies (electron decay, neutrino decay etc.) Igor Machulin , RRC “Kurchatov Institute “

  12. Detection principles nx + e- ->nx + e- s~10-44 cm2 Liquid scintillator (photon yield ~ 10000 photons/MeV) • High Light Yield = 500 photoelectrons/MeV Good energy resolution – 5% for 1 MeV • Very low energy threshold ~ 60 keV • Good position reconstruction of events • The key requirement for measurements is the extremely low radioactive contamination ! To be less than Solar neutrino rate ~50 counts/(day*100 tons) Electron recoil spectrum due to solar neutrino scattering Simulated electron spectrum in Borexino from Solar  (SSM+LMA) and backgrounds pp 7Be CNO, pep 8B Igor Machulin , RRC “Kurchatov Institute “

  13. Light Yield and Energy Resolution 14C spectrum in Borexino detector (end point ofbdecay-156 keV) The Light Yield is calculated by global fit on the experimental Borexino spectrum: 14C – 156 keV end-point, 11C –+ decay, Q=1.98 MeV 7Be n Compton edge - 665 keV 210Po alpha peak resolution - s 210Po Light yield = 500pe/MeV Energy resolution is obtained from 210Po alpha-decays peak ( Q=5.41 MeV, quenched by a factor ~13) s/E = 5% at 1 MeV 14C content in Borexino scintillator- 2.7 * 10-18 14C/12C Igor Machulin , RRC “Kurchatov Institute “

  14. Cosmic muon rejection in Borexino after μ cut • Cosmic μ flux - 1.21±0.05 h-1m-2 • μ detected in Outer and Inner Detector • Outer Detector efficiency > 99% • Inner Detector μ analysis is based • on time pulse shape variables • Estimated overall rejection factor: > 104 • After cuts, mbackground: • < 1 c/d/100 ton Measured μ angular distributions Igor Machulin , RRC “Kurchatov Institute “

  15. Position reconstruction of events • Based on time of flight fit to the time distribution of detected photoelectrons • cross checked on selected events : 14C, 214Bi-214Po, 11C,external gammas, teflon laser light diffusers on the Inner Vessel detector surface. external events on the surface R=4.25m. Radius cut Internal events R<4.25m. Radius (m) Spatial resolution of reconstructed events: 16 cm at 500 keV scaling as (Npe)-1/2 1,25 m of scintillator in all directions assures a shielding for the background from the PMTs and the nylon of the vessel. Additional cut |z|<1.7m Total effective fiducial volume after the position cut - 78.5 tons Igor Machulin , RRC “Kurchatov Institute “

  16. a/bdiscrimination of events Full separation at high energy Small deformation due to average SSS light reflectivity a particles b particles ns GATTI Parameter is applied to the statistical subtraction of a near the 210Po peak low energy side of the 210Po peak 2 gaussians fit 2 gaussians fit a/b Gatti parameter a/b Gatti parameter Igor Machulin , RRC “Kurchatov Institute “

  17. t = 432.8 ns b a 212Bi 212Po 208Pb ~800 KeV eq. 2.25 MeV Background - 232Th content in scintillator 212Bi-212Po correlated eventsin the scintillator z (m) =423±42 ns Time (ns) (m) 232Th: (6.8+-1.5)×10-18 g/g – 0.25 cpd/100 tons Igor Machulin , RRC “Kurchatov Institute “

  18. t = 236 ms b a 214Bi 214Po 210Pb ~700 KeV eq. 3.2 MeV Background - 238U content in scintillator 214Bi-214Po correlated eventsin the scintillator: z (m) =240±8  s Time (s) (m) 238U: (1.9+-0.3)×10-17 g/g - 2 cpd/100 tons Igor Machulin , RRC “Kurchatov Institute “

  19. b g 85Kr 85mRb 85Rb 514 keV 173 keV • = 1.46 ms - BR: 0.43% Background- other contaminants in scintillator 210Po - a-decay,Q=5.41 MeV , LY quenched by a factor~13 • (~ 60 cpd/ton was inserted during • the scintillation filling) • 210Po background is related neither to 238U contamination nor to 210Pb contamination • it is decaying with a t200 days • -removed from the spectrum viaa/b discrimination technique 85Kr - b -decay, Q=687 keV studied by delayed coincidence: the 85Kr contamination (29+-14) counts/day/100 ton Igor Machulin , RRC “Kurchatov Institute “

  20. New experimental results for 192 days of live time (16 May 2007 – 12 April) Photoelectron raw charge spectrum in Borexino – to be published these days at arXiv:08xxxxxv1 Counts/(5 photoelectrons * day * 100 tons) Igor Machulin , RRC “Kurchatov Institute “

  21. Spectral fit of the energy spectrum with a/b statistical subtraction (192 days) Igor Machulin , RRC “Kurchatov Institute “

  22. BOREXINO new result 192 days of live time • Oscillation predictions for Mikheev-Smirnov Large Mixing Angle Solution: In Solar model BPS07(GS98) HighZ48 ± 4 c/100t/d In Solar model BPS07(AGS05) LowZ44 ± 4 c/100t/d • No oscillation hypothesis 75± 4c/100t/d Survival probability for 7Beνe - Pee=0.56 ± 0.10 The no oscillation hypothesis Pee=1 is rejected at 4s level 49±3stat±4syst7Beν counts / (day· 100 ton) Igor Machulin , RRC “Kurchatov Institute “

  23. BOREXINO

  24. Prospects of Borexino • pep and CNO Solar n fluxes • Main problem: 11C production by cosmic m 11C ->11B +e+ +ne (Q = 1.98 MeV, T1/2=20.4min), tagging in 3-fold delayed coincidence m, n (~ms) , • m track reconstruction • + position of n-capture veto region around this position for ~ 1 hour. • Required rejection factor ~ 10 CNO 11C pep • 8B n Solar flux measurements • neutrino magnetic moment search : Sensitivity on mn at few * 10-11mB level (like in best reactor experiments); with Solar n and dedicated measurement with artificial 51Cr n source Igor Machulin , RRC “Kurchatov Institute “

  25. Prospects of Borexino - Geo & reactor antineutrinos - Supernova neutrinos detection Standard SN at 10kpc Igor Machulin , RRC “Kurchatov Institute “

  26. Monitoring of CERN neutrino beam • The SPS CERN primary proton beam at 400 GeV is focused onto a graphite target, producing secondary mesons. Neutrinos are produced in a 900 m length vacuum tunnel by the decay in flight of high momentum p+ and K+ selected and focused towards the Gran Sasso Laboratory - 730 km . • The neutrino beam contains predominantly muon neutrinos with an average energy of 17 GeV, and a contamination of anti -nm, ne and anti-ne at the level of 10-2. The beam to Gran Sasso will restart in summer 2008. Direction of detected passing muons, generated by CERN n beam in Borexino detector (Sept.-Oct. 2007) Igor Machulin , RRC “Kurchatov Institute “

  27. More Info Total Scintillator Mass 0.2 Fiducial Mass Ratio 6.0 Live Time 0.1 Detector Resp. Function 6.0 Cuts Efficiency 0.3 Total 8.5 Systematic (1σ) Error [%]

  28. Spectral fit of the energy spectrum (192 days) before a/b statistical subtraction Igor Machulin , RRC “Kurchatov Institute “

  29. Neutrino Oscillations U: Pontecorvo-Maki-Nakagawa-Sakata matrix (the analog of the CKM matrix in the hadronic sector of the Standard Model). : Non-zero only of neutrinos are Majorana particles and do not enter the oscillation phenomena regardless. If neutrinoless double beta decays occurs, these factors influence its rate. The phase factor is non-zero only if neutrino oscillation violates CP symmetry.

  30. The two neutrino case The probability that a neutrino originally of flavor will later be observed as having another flavor is given by: Oscillation parameters: Solar neutrino oscillations and atmospheric oscillations are decoupled: Chooz reeactor result - Theta(1,3) < 13O

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