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Status of the BOREXINO experiment

Status of the BOREXINO experiment. Hardy Simgen Max-Planck-Institut für Kernphysik / Heidelberg for the BOREXINO collaboration. Outline. BOREXINO physics program The BOREXINO detector Scintillator purification techniques Removal of gaseous impurities 11 C background reduction

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Status of the BOREXINO experiment

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  1. Status of the BOREXINO experiment Hardy Simgen Max-Planck-Institut für Kernphysik / Heidelberg for the BOREXINO collaboration

  2. Outline • BOREXINO physics program • The BOREXINO detector • Scintillator purification techniques • Removal of gaseous impurities • 11C background reduction • Water and scintillator filling • First neutrino events: The CNGS beam • Conclusions

  3. The Borexino Collaboration • Italy (INFN & University of Milano and Genova, Perugia Univ., LNGS) • USA (Princeton Univ., Virginia Tech) • Russia (RRC KI, JINR, INP MSU, INP St. Petersburg) • Germany (MPIK Heidelberg, TU München) • France (APC Paris) • Hungary (Research Institute for Particle & Nuclear Physics) • Poland (Institute of Physics, Jagiellonian University, Cracow)

  4. BOREXINO physics program • Solar neutrinos • Supernova neutrinos • Reactor anti-neutrinos • Geological anti-neutrinos • Rare decay search

  5. Solar neutrino physics • Two types of solar neutrino experiments • Radiochemical experiments (low energy threshold, integrated flux) • Water experiments (real-time information, higher energy threshold: Only ~10-4 of total flux) • BOREXINO (and KamLAND solar phase): 1st real-time experiment at low energies

  6. BOREXINO Dm2≈ 8·10-5 eV2 27° < q < 38° Solar neutrino spectrum Vacuum oscillations Transition region Matter effects

  7. Solar neutrino physics • Measurement of 7Be-n-flux (~35 per day) • 10% measurement yields pp-n-flux with <1% uncertainty (Gallium experiments!) • Measurement of pep-n-flux (~1 per day) • directly linked with pp-n-flux • Measurement of CNO-n-fluxes (~1 per day) • Energy production in heavy stars SSM + flavour conversion

  8. Supernova neutrinos • Galactic supernova: • 10 kpc • 31053 ergs threshold: 250 keV

  9. Gran Sasso laboratory Anti-neutrino physics: European reactors ≥ 800 km baseline Averaged oscillation signal expected.

  10. Anti-neutrino physics:Geo-neutrinos from U/Th Large fraction of earth’s total heat (40 TW) from radioactivity (U/Th). Expected spectrum: KamLAND results Nature 436 (2005) 499-503.

  11. n e- n

  12. Radiopurity requirements in the BOREXINO scintillator • Expected 7Be-ν-rate: ~35 events per day • Each background contribution ≤1 event per day

  13. Suppression of radioactive background • 15 years of R&D: Development of new purification and detection techniques • Careful material selection (g-spectrometry, mass spectrometry, 222Rn emanation studies) • e.g. Inner Vessel: U/Th: ~10-12 g/g 222Rn emanation: <1 mBq/m2 • Scintillator purification: • Distillation, H2O extraction, Silicagel column, nitrogen sparging

  14. BOREXINO purification columns

  15. Counting Test Facility (CTF) Experimentally proven: Purity requirements can be fulfilled!

  16. Example: Nitrogen sparging of scintillator • Countercurrent N2/PC flow • Gaseous impurities transferred to N2 • Achievable purity determined by N2 purity • Ultrapure N2 required!

  17. BOREXINO N2 purification plant Production rate: 100 m3/h 222Rn ≤0.5 Bq/m3 (STP)  ≤1 222Rn-atom in 4 m3!

  18. Nitrogen tests • Nitrogen from different European suppliers investigated. • Several plants can produce low Ar/Kr N2 • However, strong deviations after delivery (contamination during storage, transport and refilling)  N2 delivery chain has to be tested under realistic conditions

  19. SOL LN2-tank @ MPIK Delivery chain succesfully tested: Ar: ~0.01 ppb (Goal: 0.4 ppm) Kr: ~0.02 ppt (Goal: 0.1 ppt)

  20. Spherical cut around neutron capture to reject 11C event Cylindrical cut around muon-track 11C production with neutron (95% prob) PR C 71, 055805 (2005) 11C background reduction Main background for pep / CNO neutrinos: Cosmogenically produced 11C muon track Vetoing the intersection of the 2 volumes for 5-10 11C-lifetimes. 11C production measured in CTF: PR C 74, 045805 (2006)

  21. BOREXINO filling • Long stop after spill accident in 2002 • Improvement of Gran Sasso safety and environmental standards • Operations with liquid resumed in 2006 • BOREXINO filling strategy: 1: Filling inner detector with pure water 2: Replacing water by scintillator 3: Using same (+new) water to fill outer detector

  22. PC procurement Since January:  Fresh-PC trucking from Sarroch to LNGS

  23. Background data taking started

  24. The CNGSneutrino beam nm-beam from CERN Laura Perasso

  25. First neutrino events • First CNGS run in August 2006 30 h of data taking • 55 t of water (hmax ~1.8 m) • No reconstruction, only time difference used • Expectation: 5 m-events (neutrino interactions in the rock) seen 5 events

  26. Second CNGS run in October • Detector filled with 1120 t of water (80% full), hmax ~ 10 m • 10 h of running time • Expected: 10 CNGS  events seen: 12 events

  27. A CNGS event nm from CERN

  28. Conclusions After a long forced stop: • BOREXINO water filling started in August 2006 • Scintillator filling since end 2006 • Detector is alive: Background data taking has started (not yet fully shielded) • First n-events from CNGS beam detected • BOREXINO detector expected to be in its final configuration around May  Physics data taking in 2007!

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