Neutrino Oscillations and the Sudbury Neutrino Observatory

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Solar Neutrinos
PIC2002
Art McDonald SNO Institute Queens University,
Kingston, Canada
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SOLAR FUSION CHAIN
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Solar Neutrinos

• Experimental Results
• SAGEGALLEX/GNO
• Flux 0.58 SSM
• Homestake
• Flux 0.33 SSM
• Kamiokande Superkamiokande
• Flux 0.46 SSM

Neutrino Flavor Change ?
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SSM
Experiments
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Beyond the Standard Model - n mass mixing
Vacuum Oscillations
Matter Enhanced Oscillations (MSW)
ns in matter can acquire an effective mass
through scattering (analogous to index of
refraction for light in transparent media)
Normal Matter contains many electrons, but no
muons or taus, so ne can undergo both CC and NC
scattering. Have QM two-state level crossing and
flavor change.
MSW Oscillations are dependent on the n energy
and the density of the material, hence one can
observe spectral energy distortions.
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Matter Enhanced n Oscillations
MSW gives a dramatic extension of oscillation
sensitivity to potential regions in Dm2
LMA
SMA
Solar n data are consistent with the MSW
hypothesis.
LOW

• But only circumstantial evidence
• Need definitive proof
• Appearance measurement
• Independent of SSM

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Solar Model Independent Measurements
SuperKamiokande, SNO (Using 8B Solar Neutrinos)
SuperKamiokande, SNO

• MSW Effects
• - Distortion of the spectrum
• - Regeneration in the Earth (Day/Night Effects)

• Other Time Dependent Effects
• - Seasonal effects (Earth-Sun Distance,
  Neutrino Magnetic Moments ..)
• - Long Term Solar cycle (Neutrino Magnetic
  Moments )

SNO

• Charged Current to Neutral Current comparisons
• - Electron Neutrino flux compared to Total
  Active Neutrino flux

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• Spectral Distortion From MSW

Charged Current (SNO)
Elastic Scattering (SK, SNO)
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Superkamiokande
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Superkamiokande
Also Limit on Anti-electron neutrinos few of
Standard Solar Model
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Including SK Day and Night Spectra
Fogli et al. hep-ph/0106247
Active Neutrinos
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Solar Model Independent Measurements
SuperKamiokande, SNO (Using 8B Solar Neutrinos)
SuperKamiokande, SNO

• MSW Effects
• - Distortion of the spectrum
• - Regeneration in the Earth (Day/Night Effects)

• Other Time Dependent Effects
• - Seasonal effects (Earth-Sun Distance,
  Neutrino Magnetic Moments ..)
• - Long Term Solar cycle (Neutrino Magnetic
  Moments )

SNO

• Charged Current to Neutral Current comparisons
• - Electron Neutrino flux compared to Total
  Active Neutrino flux

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Sudbury Neutrino Observatory
1000 tonnes D2O
Support Structure for 9500 PMTs, 60 coverage
12 m Diameter Acrylic Vessel
D2O
1700 tonnes Inner Shielding H2O
5300 tonnes Outer Shield H2O
H2O
Urylon Liner and Radon Seal
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n Reactions in SK, SNO

• Both SK, SNO
• Mainly sensitive to ne,, less to n? and n?
• Strong directional sensitivity

• Good measurement of ne energy spectrum
• Weak directional sensitivity ? 1-1/3cos(q)
• ne only.

• Measure total 8B n flux from the sun.
• Equal cross section for all n types

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Solar Neutrino Physics From SNO
Flavor change/oscillations
Fcc
ne
June 2001

Fes
ne 0.154(nm nt)
Fcc
ne

April 2002
Fnc
ne nm nt
April 2002
Total 8B Solar Neutrino Flux
June 2001
April 2002
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SNO Run Sequence

• Neutron Detection Method
• Capture on D
• Capture on Cl
• Capture on 3He
• Event by event separation of CC and NC events

The Three Phases

• Pure D2O
• Good CC sensitivity
• Added Salt in D2O
• Enhanced NC sensitivity
• Neutral Current Detectors
• 3He proportional counters in the D2O

Nov. 1999- May 2001
n ? d ? t ? g ? e? (Eg 6.3 MeV)
Counting Since June 2001
n ? 35Cl ? 36Cl ? ?g ? e? (E?g 8.6 MeV)
n ? 3He ? p ? t
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Signals in SNO (Monte Carlo, Renormalized)
Pure D2O
X 0.45
X 1/3
9 NHIT/MEV
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SNO Energy Calibrations
6.13 MeV
19.8 MeV
252Cf neutrons
bs from 8Li gs from 16N and t(p,g)4He
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Cuts to remove Instrumental Background
Contamination measured with independent cuts
Signal loss measured with calibration sources
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Backgrounds
Sources
Consequences
Low Energy Threshold

• High Energy Rock Gammas
• Uranium Chain
• Thorium Chain
• Muon spallation products
• PMT b-g
• Instrumental Backgrounds

Fiducial Volume Cut
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Measuring U/Th Content

• Ex-situ
• Ion exchange (224Ra, 226Ra)
• Membrane Degassing (222Rn)
• count daughter product decays

• In-situ
• Low energy data analysis
• Separate 208Tl 214Bi
• Using Event isotropy

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The data set is used for a hypothesis test of no
neutrino oscillations by assuming no MSW
distortion and comparing NC and CC. rates
Nucl-ex/0204008
Nucl-ex/0204009
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Signal Information

• Hits and Energy

• Direction from Sun

• Radial Response

n ? d ? t ? g ? e? (Eg 6.25 MeV)
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Shape Constrained Signal Extraction Results
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Shape Constrained Neutrino Fluxes

• Signal Extraction in FCC, FNC, FES.

ETheshold gt 5 MeV
Signal Extraction in Fe, Fmt.
Fmt is 5.3 s from zero ! Clear evidence for
Flavour Change !
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Solar Neutrino Flux

• 8B SSM Flux (BP01)

F(nx) 5.05 x106 cm-2s-1

• 8B SSM Flux First SNO Result (SNO SK)

• Signal extraction in R3, cosqSun, Energy
  (Constrain)

Signal extraction in R3, cosqSun only
F(nx) 6.42 (stat.) (syst.) x106
cm-2s-1
1.57
0.55
-1.57
-0.58
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Charged Current Energy Spectrum
CC spectrum normalized to predicted 8B spectrum.
? no evidence for shape distortion.
CC spectrum derived from fit without constraint
on shape of 8B spectrum above 6.75 MeV
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SNO Separate Spectra For Day and Night
Difference Spectrum
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Day - Night
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LSND
?? n? -gt ne
Particle Data Group 2000
Atmospheric
n? -gt n?
Solar
X
ne -gt nactive
X
X
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Holanda and Smirnov hep-ph/0205241
Less than Maximal Mixing at 3 s
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Holanda and Smirnov hep-ph/0205241
Non-maximal mixing Robust under change of other
parameters
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STERILE NEUTRINOS??
!!
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4 Neutrino Models
B. Kayser Neutrino 2002
Bahcall, Gonzales-Garcia, Pena-Garay hep-ph/020419
4 Uncertainty on solar Sterile component can be
Reduced to 12 By comparison of SNO and Kamland
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Other Possible Interpretations

• Flavor-Changing Neutral Currents are still a
  possibility.
• Resonant Spin-Flavor Precession in the Sun is
  possible,
• but external restrictions on neutrino magnetic
  moments and
• Solar magnetic fields make it improbable.

Future comparisons of Kamland with solar data
will restrict the remaining possibilities
substantially. Note that Kamland uses
anti-electron neutrinos so that a comparison
with solar electron neutrinos is a broader test.
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Future Solar Neutrino Measurements

• SuperKamiokande will be back on line in
  December, 2002
• Ga experiments will continue to define low
  energy fluxes.
• SNO will pursue Solar Model Independent
  measurements
• to define oscillation parameters and neutrino
  properties
• CC-NC comparisons with much improved
  accuracy
• Improved spectral shape and Zenith angle
  information
• Anti-electron neutrino detection
• Kamland and Borexino will measure 7Be and LOW
  region.
• Many experiments are in development for pp
  neutrinos.

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Signals in SNO (Monte Carlo, Renormalized)
Pure D2O
Plus Salt
X 0.45
X 1/3
9 NHIT/MEV
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Pure D2O
Signals in SNO (Monte Carlo, Renormalized)
Plus 3He Detectors for NC

• Phase 3
• Independent
• Signals for NC
• Capture in 3He
• Suppresses
• 6.25 MeV
• Gammas from
• Capture on D

9 NHIT/MEV
NHIT will be lower by 15
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Restriction of Parameter Space
NC/CC
DAY/NIGHT ()
Holanda and Smirnov hep-ph/0205241
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SUMMARY OF SOLAR NEUTRINO MEASUREMENTS

• SNO shows 5.3 s evidence for neutrino flavor
  change to active neutrinos.
• Result is consistent with previous SNO-SK
  comparison that gave
• 3.3 s evidence.
• MSW analysis of all experiments strongly favors
  LMA solution.
• Transformation solely to sterile neutrinos ruled
  out at more than 5 s.
• Possible Sterile component strongly restricted
  by comparison with
• Atmospheric n.
• No evidence of regeneration in Earth.
• No evidence for anti-electron neutrinos.
• Time dependence shows only geometric effects.
• Future measurements of solar, reactor neutrinos
  can restrict parameters
• further.

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New International Underground Science Facility At
the Sudbury site
Proposal ( 30M) submitted to Canada Foundation
for Innovation
Approved June 19, 2002 !!!

• To build on the success of the underground
  science being done
• by SNO and pursue further measurements of
• Neutrinos from Astrophysical sources
• The next generation SNO experiment (Wavelength
  Shifter ?)
• Lower Energy Solar Neutrinos
• Other Forms of Dark Matter (WIMPS)
• PICASSO (Bubble Detectors)
• Double Beta Decay
• Low Background Counting Test Facility

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14m x 14m x 60m, Clean Area