SNO Liquid Scintillator Option

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(No Transcript)
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Introduction

• Fall 04 to Dec 06 SNO Phase III
• 3He proportional counter array now in place
• dedicated Neutral Current Detectors (NCDs)
• nominal end date 31 Dec 2006
• bring total uncertainty on 8B solar n NC signal
  below 5
• physics with heavy water will be complete
• what should be done with the detector after?

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Fill with Liquid Scintillator

• SNO plus liquid scintillator ? physics program
• pep and CNO solar neutrinos
• geo-neutrinos
• 240 km baseline reactor oscillation confirmation
• supernova neutrinos
• working name SNO

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Low Energy Solar Neutrinos

• test solar models 7Be, pep, CNO
• precision survival probability measurement pep
• observe rise in survival probability at lower
  energies lower energy 8B, 7Be, pep

from Peña-Garay
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Survival Probability Rise

• SSM pep flux
• predicted to 1-2
• allows precision test

Dm2 7.9 10-5 eV2 tan2q 0.4
SNO CC/NC
pep n
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Event Rates (Oscillated)
7Be solar neutrinos
3000 pep/year/600 tons gt0.8 MeV
using BPB2001 and best-fit LMA
3900 CNO/year/600 tons gt0.8 MeV
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11C Cosmogenic Background
muon rate in KamLAND 26,000 d-1 compared with
SNO 70 d-1
these plots from KamLAND proposal
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Real KamLAND Backgrounds
external
pep window
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pep Solar n Backgrounds

• 11C cosmogenic production
• t1/2 20 min makes this difficult to veto at
  shallower depths
• positron decay guarantees gt1 MeV energy
  deposited, right in the pep n-e- recoil window
• but at SNO depths, muon rate is small enough to
  allow easy tagging (or even tolerate this
  background without veto)
• CNO neutrinos are a background
• good energy resolution desired to see clear
  recoil edge for monoenergetic pep n
• clearly interesting, for astrophysics, first
  observation of CNO n
• radiopurity requirements challenging
• 40K, 210Bi (Rn daughter)
• 85Kr, 210Po (seen in KamLAND) not a problem since
  pep signal is at higher energy than 7Be
• U, Th not a problem if can achieve KamLAND-level
  purity

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More on pep Solar Neutrinos

• from J. Bahcall and C. Peña-Garay
• 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.
• which is to say that a pep solar neutrino
  experiment would be an alternative to a pp solar
  neutrino experiment, in some regards

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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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More on Geo-Neutrinos

• detecting geo-neutrinos from natural
  radioactivity in the Earth (U, Th) helps to
  determine the radiogenic portion of Earths total
  heat flow
• by doing so, it also tests theories of Earths
  origin based upon the Bulk Silicate Earthe.g.
  see Rothschild, Chen, Calaprice, Geophys. Res.
  Lett., 25, 1083 (1998)
• e.g. see NOW 2004 talk by G. Fiorentini

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Geo-Neutrino Signal

• terrestrial antineutrino event rates
• Borexino 10 events per year (280 tons of C9H12)
  / 29 events reactor
• KamLAND 29 events per year (1000 tons CH2)
• Sudbury 64 events per year (1000 tons CH2) / 87
  events reactor

Rothschild, Chen, Calaprice (1998)
above plot for Borexinogeo/reactor ratio at
Sudbury would be twice as high
KamLAND will soon make first detection
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SNO Geo-Neutrinos

• from G. Fiorentini
• SNO is considering move to liquid scintillator
  after physics with heavy water is completed.
  With very low reactor background, well in the
  middle of Canadian shield (an easy geological
  situation) it will have have excellent
  opportunities.
• which is to say that fundamental models are
  tested by experimental valuesif those model
  calculations and measurements (for Sudbury) have
  smaller uncertainties (than for Kamioka), what we
  learn from the experimental measurements (at
  Sudbury) has potentially greater value

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Reactor Antineutrinos

• SNO can try to confirm reactor neutrino
  oscillations
• move KamLANDs spectral distortion to higher
  energies by going to a longer baseline
• this moves KamLAND spectral distortion features
  away from the geo-neutrinos
• improves geo-neutrino detection
• spectral shape confirmation

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Top Ten List

• table from Suekanes NOON2003 talk

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Location, Location, Location
Bruce
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Bruce-SNO

• 240 km baseline places 2nd oscillation maximum
  in the middle of the reactor neutrino positron
  spectrum
• 51 events per year (no oscillation expectation)
  from 6 reactors at full power 14 GWth
• there are 2 more reactors at Bruce that may be
  restarted
• not a precision test, will not further constrain
  oscillation parametersjust a confirmation, with
  statistics like K2K (e.g. in 3 years, expectation
  of 150 events, observation of 100 events)

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KamLAND Spectral Distortion
T. Araki et al., hep-ex/0406035 (2004)
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SNO Spectral Distortion
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3 Measurements for Low Cost

• for relatively little cost, there is an
  opportunity to use existing equipment (i.e. most
  of the SNO detector) to enable new measurements
• costs are
• liquid scintillator procurement
• mechanics of new configuration
• fluid handling and safety systems
• scintillator purification

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Supernova Neutrinos

• 1 kton organic liquid scintillator would maintain
  excellent supernova neutrino capability
• ne p large rate
• ne 12C (CC)
• ne 12C (CC)
• nx NC excitation of 12C (NC)
• nx p elastic scattering (NC) large rate
• see Beacom et al., PRD 66, 033001(2002)

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SNOLAB LOI

• letter of interest submitted on 12 April 2004
• SNO option study group
• M. Chen, A. Hallin, C. Kraus, J.R. Leslie, J.
  Maneira, R. MacLellan, A.B. McDonald, A.
  Wright Queens
• M. Boulay Los Alamos
• D. Hahn, M. Yeh Brookhaven
• X. Dai Carleton
• B. Cleveland, R. Ford SNOLAB
• D. Hallman, C. Virtue Laurentian
• R.G.H. Robertson U of Washington
• potential collaborators from outside SNO have
  indicated some interest

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• fully funded expansion of SNO underground site
  into an international facility for underground
  experiments
• double beta decay
• dark matter
• solar neutrinos
• supernova neutrinos
• excavation expected to begin late 2004, completed
  by 2006
• space ready for experiments in 2007

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Technical Aspects of RD

• liquid scintillator cocktail design
• optimize optical properties (attenuation length,
  light yield, pulse-shape discrimination,
  scattering)
• chemical compatibility with acrylic
• high density preferred (r 1 g/cm3) to use with
  existing H2O buffer outside the acrylic vessel
• mechanical hold-down system
• cover gas improvements (lower radon)
• safety, fluid handling underground
• scintillator purification
• SNO detector state (surviving PMTs, acrylic
  vessel certification)
• calibrations and operations

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Schedule

• SNO RD one year
• complete technical description
• full cost estimates
• completed feasibility studies
• fully-developed science goals
• if above okay, full proposal(s) to be submitted
  11/2005
• call for new collaborators in parallel with above
• when above approved, 2 years to first fill
  (04/2008)

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Double Beta Decay SNO

• SNO plus liquid scintillator plus double beta
  isotopes SNO
• add bb isotopes to liquid scintillator
• dissolved Xe gas (2)
• chemical loading (Nd, Se, Te)
• dispersion of nanoparticles (Nd2O3, TeO2)
• enormous quantities (high statistics) and low
  backgrounds trade off for poor energy resolution
  of liquid scintillator

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Candidate Selection
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2n bb Background
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Test ltmngt 0.150 eV

• 0n 1057 events per year with 1 Nd- loaded
  liquid scintillator (natural Nd)
• S/B 0n/2n (upper half peak) 2.3
• crude illustration below

statistical test of the shape to extract 0n and
2n components!
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Summary

• RD to develop SNO underway
• staged approach envisioned
• deployment of pure scintillator for antineutrinos
• next stage go for purification to try for low
  energy solar neutrinos
• next stage deploy double beta (e.g.
  nanoparticles), would jump to this stage ASAP
• long-term program provides steady and early
  science output for SNOLAB
• new collaborators are welcome