SNO with Liquid Scintillator

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SNO with Liquid Scintillator

• M. Chen

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Why Liquid Scintillator?

• from 9 NHIT/MeV to up to 600 p.e./MeV
• pep and CNO solar neutrinos
• geo neutrinos
• can make an interesting reactor neutrino
  oscillation measurement also
• 7Be solar neutrinos are also interesting maybe
  KamLAND or Borexino will observe them or maybe
  not
• some of the above measurements could ONLY be made
  at SNO depths

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Why pep solar neutrinos?

• solar model flux uncertainty is 1.5
• cross section n-e- scattering (no uncertainty)
• rate measurement at the level is possible
• 3000 events per year in 600 fiducial tons (LMA
  oscillated)

pp and pep solar neutrinos are standard candles
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Low Energy Solar Neutrinos
7Be solar neutrinos have a huge rate in
comparison!
3000 pep/year/600 tons gt0.8 MeV
3900 CNO/year/600 tons gt0.8 MeV
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pep Neutrino Backgrounds

• KamLAND (and to a lesser extent Borexino) cannot
  detect pep solar neutrinos due to underground 11C
  cosmogenic production
• 20 minute half-life of 11C cannot be vetoed
• positron decay guarantees 1 MeV energy deposited,
  right in the pep n-e- recoil window
• CNO neutrinos are a background
• good energy resolution desired to see clear
  recoil edge for monoenergetic pep n
• radiopurity requirements likely to be challenging
• U, Th, K, 210Bi (Rn daughter) Qb 1.2 MeV
• 85Kr, 210Po (plaguing KamLAND) not a problem
  since pep signal is at higher energy than 7Be

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11C Cosmogenic Background
from KamLAND proposal
muon rate in KamLAND is 26,000 per day!
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• if you could achieve KamLAND scintillator purity
  at SNO depths, you could observe the pep and CNO
  solar neutrinos
• Our global analyses show that a measurement of
  the n-e scattering rate by pep solar neutrinos
  would yield essentially equivalent information
  about neutrino oscillation parameters and solar
  neutrino fluxes as a measurement of the n-e
  scattering rate by pp solar neutrinos. (Bahcall
  and Peña-Garay)

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KamLAND!

• spectral distortion?
• geo neutrinos?
• spectral distortion hiding under the geo
  neutrinos?
• Q how much do we know about the geo neutrinos?
• A not enough to go looking for spectral
  distortions

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Antineutrino Geophysics

• can we detect antineutrinos from b- decay of U
  and Th in the Earths mantle and crust?
• knowing Earths total radioactivity would be very
  important for geophysics
• understanding thermal history of the Earth
• thought to account for 40 total heat generation
• dominant heat source driving mantle convection
• how much in the mantle and the crust?

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Antineutrino Spectrum (for Borexino)
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Terrestrial Antineutrino Flux

• Gran Sasso 6.9 x 106 cm-2 s-1
• Kamioka 3.7 x 106 cm-2 s-1
• Sudbury 8.2 x 106 cm-2 s-1
• South Pole 4.1 x 106 cm-2 s-1
• terrestrial antineutrino event rate
• Borexino 10 events per year (280 tons of C9H12)
• KamLAND 29 events per year (1000 tons)
• Sudbury 64 events per year (1000 tons CH2)
• background from nuclear reactors
• Borexino 29 events per year
• KamLAND 750 events per year
• Sudbury 87 events/year

Rothschild, Chen, Calaprice, Geophys. Res. Lett.
25 1083, (1998)
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Global Geo Neutrinos

• KamLAND and SNO contrast
• SNO geo neutrino measurement is more insensitive
  to local crustal geology, since it is surrounded
  by Canadian shield (thick continental crust)
• KamLAND is near the junction of continental and
  oceanic crust (with different U and Th content)
  at the Pacific plate boundary more local
  variation
• Best information would be to have geo neutrino
  measurements from both sites. Multiple site data
  starts to allow mantle contribution to be
  separated from the crustal contribution (when
  crustal model information is included

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Reactor Neutrino Oscillation Confirmation

• Bruce to SNO 240 km baseline
• 51 events per 1 kton-yr exposure with six Bruce
  reactors at full power 14 GWthermal
• not a ridiculous event rate for doing physics
  (e.g. similar to K2K, or KamLANDs first results)
• move KamLANDs spectral distortion by changing
  baseline
• additional 36 events per kton-yr exposure for
  Pickering and Darlington at 16 GW_th full power
  (300 km)

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Move the Spectral Distortion
the 175 km survival probability plot is only an
approximation for KamLAND since KamLAND has many
reactors at different baselines, averaging out
spectral distortion features LMA Dm2 7 10-5
eV2 puts the first oscillation max at too high
energy and the 2nd oscillation max at too low
energy (geo neutrinos) some people have proposed
going closer, to bring the 1st oscillation max in
range could also go farther (Bruce-SNO) to move
up 2nd osc max
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Reactor neutrinos

• goal is demonstration of oscillations via a sharp
  spectral distortion, at 4 MeV, right in the
  middle of the reactor neutrino spectrum
• Real benefits from moving the spectral distortion
  away from the geo-neutrinos (benefiting both)

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Summary

• pep and CNO solar neutrinos
• geo neutrinos
• can make an interesting reactor neutrino
  oscillation measurement also
• 7Be solar neutrinos are also interesting
• Starting point for a variety of scintillator
  based experiments involving additives