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Status and Prospects of Borexino G. Ranucci NOW 2006 Conca Specchiulla September 11, 2006

Status and Prospects of Borexino G. Ranucci NOW 2006 Conca Specchiulla September 11, 2006. Summary of the talk Description of the architecture of the detector Status of the installations and operations Near future fill and operation schedule Physics with Borexino

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Status and Prospects of Borexino G. Ranucci NOW 2006 Conca Specchiulla September 11, 2006

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  1. Status and Prospects of Borexino G. RanucciNOW 2006Conca SpecchiullaSeptember 11, 2006 Summary of the talk Description of the architecture of the detector Status of the installations and operations Near future fill and operation schedule Physics with Borexino CTF in the framework of the Borexino project Conclusions

  2. Borexino is a massive calorimetric liquid scintillation detector aimed at the real time detection of the 7Be solar neutrino flux Main challenge: radiopurity !

  3. Borexino Collaboration • Virginia Tech (USA) • College de France (France) • Princeton Univeristy (USA) • Technical University Munich (Germany) • JINR Dubna (Russia) • Kurchatov Institute Moscow (Russia) • MPI Heidelberg (Germany) • Jagellonian University Cracow (Poland) • INFN – Milano (Italy) • INFN – Genova (Italy) • INFN – Perugia (Italy) • INFN – LNGS (Italy)

  4. Laboratori Nazionali del Gran Sasso 3700 mwe overburden

  5. Schematic view of the Borexino experiment • Borexino features a shell structure - Components of the detector (from center): • Scintillator: PC + PPO (1.5 g/l) (300 tons, 100 tons fiducial mass) • Nylon inner vessel (d = 8.5 m) - Nylon outer vessel • Buffer liquid: PC + DMP (1040 ton) • Stainless steel sphere (d = 13.7 m) • 2200 inner phototubes - 1800 equipped with light concentrators • Outer Muon veto: 210 outer phototubes plus diffusive tyvek panels • External buffer of ultra-pure water • Water Tank (h and d = 18 m ) • Calibrations equipments • Electronics and DAQ

  6. Purification and other ancillary plants (I) • Purification systems • Purification skids • Distillation • Water extraction • Nitrogen stripping • Module 0 • Silica gel column • CTF purification skid • Water extraction of the concentrated PPO solution

  7. Purification and other ancillary plants (II) • Storage vessels and associated pumping stations • Nitrogen and synthetic air plants • Regular nitrogen • Purification equipment →high purity nitrogen • LAK Nitrogen (low content argon and krypton nitrogen) • Synthetic air line (used for vessel inflation) • PPO plant – preparation of the master solution (PPO concentrated solution) • DMP plan – buffer quencher • Interconnection system – path of the scintillator through the various plants • Exhaust system – to reduce the PC vapors content in the nitrogen • PC unloading station

  8. Purification and ancillary plants (III) • Filling Stations – for the PC and water fill of the detector • Water purification plant - to purify the raw water • Borexino water loop – to feed and re-circulate the water in the Water Tank • Emergency systems • Blow down • Fire extinguishing equipments • Centralized control system • Clean rooms • Some used in the installation phase of the detector • That on top of the Water Tank hosts part of the filling stations – access to the detector for calibration

  9. Calibrations • A variety of calibration and monitoring systems are planned • Laser pulses distributed to all PMT’s with a fiber optics splitting system • Timing calibration • Gain adjustment via detection of the single photoelectron peak • External sources (Th) located in the SSS close to the light cones • Check of the stability in time of the overall detector response • Internal sources inside the scintillator • Position calibration • Energy calibration • a/b discrimination

  10. Calibrations • CCD Cameras with capability to locate precisely (±2 cm) objects inside the detector (translates into a ≤ 2% uncertainty in the FV definition) • Laser beams with different wavelengths through the buffer and laser excitation of the scintillator • Stability monitoring of the optical properties • Blue LED’s + fibers for the outer muon veto detector • Calibration of the overall detector response via a sub-MeV n-source (51Cr)

  11. Water Tank (1999)

  12. Stainless Steel Sphere (2000)

  13. Phototubes in the SSS (2001)

  14. Vessel in SSS prior to inflation as viewed from CCD cameras (2004)

  15. SSS – PMT’s – Vessel inflated as viewed from CCD cameras

  16. Last phototubes on the bottom of the sphere and on the 3 m door

  17. Closing of the big door of the sphere (June 2004)

  18. Muon veto: tyvek and phototubes on the external surface of the sphere

  19. Tyvek on the lateral wall of the Water Tank

  20. Tyvek under the dome of the Water Tank

  21. Electronics racks

  22. Status of the activity as September 2006 • Detector installation – essentially completed (SSS closed in June 2004, only few piece of hardware missed in the Water Tank) • Purification and fluid handling systems – Installation completed, cleaning and commissioning almost completed (in 2005 and beginning of 2006, after substantial alleviation of the underground operation constraints, but water discharge not yet allowed; only some final cleaning missed) • Calibration hardware – CCD cameras and external source insertion system completed, hardware to deploy the internal sources to be finalized • Filling – Water Fill of the Sphere in progress (water discharge still by truck, full operation capability via normal discharge expected in few weeks) • CNGS – data taking during the August run accomplished successfully

  23. Status of Borexino during the August CNGS run • The filling of the Borexino Stainless Steel Sphere (SSS) has started on August 1°, 2006 • During this run, about 55 t of water were present • The height of the water from the bottom of the SSS is about 1.8 m • Active surface ~ 10.5 m2 Beam direction

  24. Current acceptance and target mass Hall-C Side view Borexino CTF Opera Hall-C Top view L. Perasso Water level heigth: 1.8 m Target Mass: 55 t (not relevant and not considered in this run)

  25. Preliminary evidence for signal (1) GPS clock time difference between BX event and nearest previous CNGS time stamp Binning: 50 ms ms

  26. Preliminary evidence for signal (2) GPS clock time difference between BX event and nearest previous CNGS time stamp Binning: 50 ms Zoom of 0-100 ms interval ms

  27. Preliminary evidence for signal (3) 5 events at 2.4 ms delay (binning 50 ms) No other bin but one has more than 1 except out of 3200 events in 8000 bins Expected CNGS events: 5 Expected cosmic muons: ~ 2000 Probability of bck fluctuation: < 2. 10-5 ms

  28. Near future perspectives • Filling Operations • Sphere full of water by the middle of November 2006 (expectation is to complete the fill with the full discharge capability) • SSS and Nylon Vessel PC fill to be started by the middle of December 2006. The PC will be delivered from the production plant in Sardinia to Gran Sasso via special transportation trucks, and then passed through the distillation unit prior to be mixed with the PPO and inserted in the detector. Detector full of PC by May 2007 • Water Tank water fill to be carried out in parallel with the first phase of the PC fill from the middle of December. Completed in two months • Data Taking phases • CNGS beam monitor – throughout the October 2006 run with about all the water in the SSS (and then with PC for future beam on periods) • PC runs – Preliminary runs since the beginning of the fill (radiopurity check). Run in full configuration: from middle of 2007 • Meanwhile source calibrations in various steps

  29. Monocromatic ! En=862 keV FSSM=4.8x109n/sec/cm2 s=10-44 cm2 “n window” (0.25-0.8 MeV) expected rate (LMA hypothesis) is 35 counts/day in the neutrino window

  30. Physics goals for Borexino • Measure 7Be solar neutrinos (0.25-0.8 MeV) • Measured vs MSW-LMA predicted event rate • Time variation of solar signal in the sub-MeV range • Study CNO and pep neutrinos (0.8-1.3 MeV) (rejection of 11C cosmogenic background – proved in CTF hep-ex/0601035) • Neutrinos from the Earth • Neutrinos form supernovae • Neutrino magnetic moment (also in conjuction with the 51Cr source calibration)

  31. Radiopurity constraints • This translates into the following requirements on the most critical contaminants (238U , 232Th , 40K, 210Po, 210Pb, 39Ar, 85Kr) : • To lower the threshold down to 250 keV, it is mandatory to reach very high radiopurity levels in the active part of the detector ; Intrinsic contamination of the scintillator for what concerns isotopes belonging to the U and Th chain  10-16 g/g; 14C /12C 10-18 in the scintillator Intrinsic contamination of the scintillator for what concerns 40K  10-14 g/g; Contamination of the nylon vessel for what concerns the U and Th chain  10-12 g/g; Constraints on N2 used to sparge scintillator: 0.14 ppt of Kr in N2 (0.2 mBq 85Kr/m3 N2) Constraints on N2 used to sparge scintillator: 0.36 ppm of Ar in N2 (0.5 mBq 39Ar/m3 N2) Contamination of the buffer liquid in U and Th chain  10-14 g/g; Contamination of the external water in U and Th chain 10-10 g/g; Each of these points required careful selection and clean handling of materials, + implementation of purification techniques

  32. Counting Test Facility (CTF) • CTF is a prototype of BX. Its main goal was to verify the capability to reach the very low-levels of contamination needed for Borexino • CTF campaigns • CTF1: 95-97 • CTF2: 2000 (pxe) • CTF3: 2001 still ongoing • 100 PMTs • 4 tons of scintillator • 4.5m thickness of water shield • Muon-veto detector CTF high mass and very low levels of background contamination make it a unique detector to search for rare or forbidden processes with high sensitivity

  33. CTF Radiopurity results 238U = (3.5 ± 1.3)  10-16 g/g 232Th = (4.4 ± 1.5)  10-16 g/g 14C/12C = (1.85 ± 0.13)  10-18 Breakthrough results in the field of ultra-low radioactive contaminations, opening the path toward the real time solar neutrino detection in the sub-MeV region Furthermore, realization of the importance of the background induced by 85Kr and 210Pb – 210Po and demonstration of capability to cope with them through a suitable combination of water extraction, distillation and silica gel column purification techniques

  34. Some physics results • Limit on the neutrino magnetic moment at the level of 5.5x10-10mB[Borexino coll., Phys. Lett. B 563 (2003)] 37 • Limit on the electron stability [Borexino coll., Phys. Lett. B 525 (2002)] • Limits on nucleon decay into invisible channels [Borexino coll., Phys. Lett. B 563 (2003)] 23 • Limit on the violation of the Pauli exclusion principle [Borexino coll.,Eur.Phys. J. C37 (2004) 421] • Limit on antiuneutrino flux from the Sun (threshold 1.8 MeV) <1.1105 cm-2s-1

  35. Conclusions • The installation of the detector is completed • The purification and ancillary plants are essentiall all ready, cleaned and commissioned • The first phase of the fill (water fill) is in progress - expected to be completed by beginning of November • Final PC fill to be started in December, to be completed by May • Overall instrument working fine as provedby the data taking during the August CNGS run • From next Spring/Summer data taking with the detector in the final configuration

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