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

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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

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

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Laboratori Nazionali del Gran Sasso
3700 mwe overburden
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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

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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
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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
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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
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• Calibrations
• A variety of calibration and monitoring systems
  are planned
• Laser pulses distributed to all PMTs 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

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• 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 LEDs fibers for the outer muon veto
  detector
• Calibration of the overall detector response via
  a sub-MeV n-source (51Cr)

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Water Tank (1999)
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Stainless Steel Sphere (2000)
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Phototubes in the SSS (2001)
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Vessel in SSS prior to inflation as viewed from
CCD cameras (2004)
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SSS PMTs Vessel inflated as viewed from CCD
cameras
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Last phototubes on the bottom of the sphere and
on the 3 m door
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Closing of the big door of the sphere (June 2004)
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Muon veto tyvek and phototubes on the external
surface of the sphere
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Tyvek on the lateral wall of the Water Tank
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Tyvek under the dome of the Water Tank
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Electronics racks
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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
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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
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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)
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Preliminary evidence for signal (1)
GPS clock time difference between BX event and
nearest previous CNGS time stamp Binning 50 ms
ms
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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
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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 lt 2. 10-5
ms
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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
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n window (0.25-0.8 MeV)
expected rate (LMA hypothesis) is 35 counts/day
in the neutrino window
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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)

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Radiopurity constraints

• To lower the threshold down to 250 keV, it is
  mandatory to reach very high radiopurity levels
  in the active part of the detector

• This translates into the following requirements
  on the most critical contaminants (238U , 232Th ,
  40K, 210Po, 210Pb, 39Ar, 85Kr)

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
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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
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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
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• Some physics results
• Limit on the neutrino magnetic moment at the
  level of 5.5x10-10 mB 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) lt1.1?105 cm-2s-1

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• 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 proved by the
  data taking during the August CNGS run
• From next Spring/Summer data taking with the
  detector in the final configuration