Solar Neutrino Oscillations Dm2, q12

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Solar Neutrino Oscillations(Dm2, q12)
Background (aka where we were) Radiochemical
experiments Kamiokande and Super-K Where we
are Recent results SNO and KamLAND Global
picture Where we are going Upcoming
Results Future Measurements?
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Background
Solar Neutrino Problem The deficit of ne
observed from the sun compared to solar
model Predictions was a longstanding puzzle,
dating from Ray Davis first 37Cl experiment in
the 1960s. Neutrino Oscillations Experiments
were primarily sensitive to ne, so flavor change
from ne to nm,t could account for the
difference MSW Effect (Mikheev-Smirnov-Wolfenst
ein) Forward scattering of neutrinos passing
through matter is flavor-dependent propagation
through matter is different than in vacuum. Key
element of understanding solar neutrino
oscillations
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Neutrino Oscillations

• MNSP (Maki-Nakagawa-Sakata-Pontecorvo) matrix in
  the lepton
• sector analogous to the CKM matrix in the quark
  sector
• Solar neutrino oscillations are dominated by
  q12
• to good approximation we can neglect 1-3 mixing
• Electron neutrino survival probability is
• If we can average over oscillations, this is
  just

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MSW for World Leaders

• MSW effect modifies the ne survival probability
• For production in matter with electron density
  ne
• Simple (and useful) limiting cases
• Below critical energy,
• vacuum oscillations dominate
• Above critical energy
• matter effects dominate
• Critical energy 1.8 MeV for LMA, 8B
• Goes as 1/Dm2

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The Sun as a Neutrino Source

• Complicated energy spectrum
• Different experiments sensitive
• to different energy regions
• Oscillations averaged out sun
• larger than oscillation length
• (except for smallest Dm2)
• Annual variation
• 1/R2, baseline change
• Day/night effects?
• MSW effect in the earth
• Different components produced
• at different places in the sun

91
7
0.2
0.008
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Radiochemical experiments

• ne capture on select radioisotopes
• Chlorine ne 37Cl ? e 37Ar gt 814 keV
• Gallium ne 71Ga ? e 71Ge gt 233 keV
• Detect decays of capture daughters
• Sensitive only to integrated ne flux above
  threshold
• Results
• Homestake (Cl) ?Cl/SSM 0.34 ? 0.03
• SAGEGALLEX/GNO ?Ga/SSM 0.54 ? 0.03
• (SSM is Standard Solar Model,
• BP00 Bahcall/Pinsonneault,Astrophys. J. 555,
  990, 2001)

Ray Davis
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Kamiokande / Super-K

• Water-Cerenkov detectors
• Detect forward-scattered electrons from
• neutrino-electron elastic scattering
• nx e ? nx e
• Sensitive to nm,t as well as ne s(nm,t) ? 0.15
  s(ne)
• Real-time detection of electron energy and
  direction
• Only sensitive to most energetic 8B solar
  neutrinos
• Flux result ?SK/SSM 0.465 ? 0.015

Koshiba Masatoshi
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Kamiokande / Super-K

• Directional information gives clear
• evidence that neutrinos come from
• the sun
• 7 seasonal variation
• consistent with 1/R2
• Day/night (zenith angle) effects small
• constrains earth MSW effect
• ADN 0.021 ? 0.020 (2 )

0.013 N-D - 0.012 ND
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Allowed regions, pre-SNO, KamLAND

• Four very different allowed
• regions in Dm2, tan2q space
• Many solutions at large or
• maximal mixing
• Why tan2q?
• MSW effect is different for
• m1ltm2 and m1gtm2 cases
• tan2qgt1 means m1gtm2
• Oscillation equations symmetric under
• q ? (p/2 - q), Dm2 ? -Dm2
• Super-K zenith angle distribution
• inconsistent with SMA

LMA
SMA
LOW
VAC
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SNO

• Heavy-water-Cerenkov detector, 5 MeV threshold
• Three different n detection modes
• CC (charged current) ne D ? p p e ne
  only
• NC (neutral current) nx D ? p n nx all
  three flavors!
• ES (elastic scattering) nx e ? nx
  e (same as Super-K)
• Neutron detection done in three different ways
• Phase I (D2O phase) 2H n ? 3H g (6.25
  MeV) 25
• add NaCl
• Phase II (salt phase) 35Cl n ? 36Cl g (8.6
  MeV) 83
• NaCl out, Neutral Current Detectors (NCDs) in
• Phase III (NCD phase) n detection via 3He
  proportional counters
• 45 neutron detection efficiency, but much
  cleaner S/B
• Complicated analysis the three signals are all
  backgrounds to each other

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Sudbury Neutrino Observatory

• NC, CC, ES rates all measured
• NC sees full SSM flux!
• Solar neutrino problem solved
• 5.3s appearance of nm,t in a ne beam
• Ratio of CC to NC strongly
• constrains the mixing angle q12
• CC/NC 0.306 ? 0.026 ? 0.024
• Day/night asymmetry (ne only)
• ADN 7.0 ? 4.9

1.3 - 1.2
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SNO oscillation parameter constraints
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KamLAND

• Kamioka Liquid-Scintillator AntiNeutrino
  Detector
• Looking for disappearance of antineutrinos
  produced in
• nuclear reactors with LMA mixing parameters
• Baselines on the order of the oscillation length
• No significant MSW effects
• Liquid scintillator calorimeter, sub-MeV
  threshold
• Inverse b-decay ne p e n
• Coincidence signal
• prompt e annihilation (E En ? 0.8 MeV)
• delayed n capture (190 ms) (E 2.2 MeV)
• No directional information

Detected ne spectrum (no oscillations)
Inverse b-decay cross-section
Reactor ne spectrum
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Antineutrinos from Japanese reactors

• Sum over ensemble
• of reactors
• 80 of flux from
• baselines 140-210 km
• Variable flux!

KamLAND
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Effects of Oscillations

• Oscillations change both the
• rate and energy spectrum
• of detected events
• Multiple reactors at different
• baselines complicate the
• signal
• Reactor operation data is
• critical

Example spectra (L.A.Winslow) Top Dm21.5?10-4,
tan2q 0.41 (LMA II) Bottom Dm20.7?10-4,
tan2q 0.41 (LMA I) top 4 reactors at full
thermal power only
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Antineutrino Rate Analysis

• Observed 54 (145.1 days livetime)
• No-oscillation expectation 86.8 ? 5.6 (syst)
• Background 1 ? 1
• (NobsNBG)/Nno-osc 0.611 ? 0.085 (stat) ?
  0.041 (syst)
• (statistics above on 54 events)
• Probability that 86.8 events would
• fluctuate down to 54 is lt 0.05
• Standard ne propagation
• is ruled out at the
• 99.95 confidence level

curve, shaded region global-fit solar LMA
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Rate Shape Analysis

• Fit prompt (positron) energy spectrum above 2.6
  MeV with
• full reactor information (power, fuel, flux),
  2-flavor mixing
• Energy spectrum shape provides additional
• constraints on oscillation parameters

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KamLAND parameter constraints
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Global Fits
SNO Global Fits

• Two different global fits
• General conclusions
• Maximal mixing
• ruled out at 5.3-5.4s
• LMAII strongly disfavored
• Best fit points
• tan2q ? 0.40
• Dm2 ? 6.5 x 10-5 (solar only)
• ? 7.1 x 10-5 (w/KamLAND)

solar only
with KamLAND
Holanda Smirnov Global Fits
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Future Measurements SNO

• D2O phase complete, published
• Salt phase complete
• analysis of first half of data published
• analysis of full salt dataset in progress
• NCDs being installed now
• SNO will continue to improve
• its measurements
• Better measurement of CC/NC ratio
• will improve tan2q constraints
• Improved day/night asymmetry can
• better constrain Dm2 in solar-only fits

HolandaSmirnov
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Future Measurements KamLAND

• KamLAND continues to collect reactor neutrino
  data
• gt 3x the first published dataset already
• Also working to understand our detector better
• e.g. 4p calibration system
• KamLAND can provide the best Dm2 constraint and
• a good tan2q constraint from reactor analysis

• Monte Carlo study
• 1000 sets of 500 events for each of
• LMA II Dm21.5?10-4, tan2q 0.41
• LMA I Dm20.7?10-4, tan2q 0.41
• Top 16 reactors, full thermal power,
• energy resolution smearing
• Fit for mixing parameters with
• shape-only analysis above 2.6 MeV
• No systematics included
• Clear separation of LMA I and LMA II
• Better fractional resolution on Dm2 for
• LMA I (4) than LMA II (5) (95 CL)
• tan2q12 to ? 0.2 level (95 CL)
• (without rate!)

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7Be solar neutrino measurement?

• Idea directly detect solar 7Be neutrinos
• Measurement of single energy deposition from
  elastic scattering
• See a Compton edge in the data
• Low energy threshold
• Low radioactive backgrounds
• are required!

• E.g.
• 238U lt 1016 g/g lt (3.5 ? 0.5)?1018 g/g
• 232Th lt 1016 g/g lt (5.2 ? 0.8)?1017 g/g
• 40K lt 1018 g/g lt 2.7 ? 1016 g/g

KamLAND proposal plots not actual backgrounds!
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7Be solar neutrino measurement?

• KamLAND
• Backgrounds in the signal region currently
• about 106 times too high
• Working on purification methods to remove
• 85Kr (from nitrogen used in purification)
• 210Pb, 210Pb (from decay of radon that got into
  the system)
• Borexino
• Has been on hold following a
• pseudocumene spill August 2002
• Recent news permission for
• limited use of water
• Hoping for vessel inflation this
• spring water fill this summer
• scintillator to follow?

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7Be solar neutrino measurement?

• What do we learn from a 7Be neutrino flux
  measurement?
• 7Be line at 862 keV is well below the MSW
  transition,
• at about 2.2 MeV, so vacuum effects dominate
• Flux suppression just depends on q12, not
  sensitive to Dm2
• SSM 7Be predictions are at the ?10 level. This
  translates
• into a larger uncertainty on q12 than current
  measurements.
• Measuring the solar 7Be neutrino flux will NOT
  improve
• our present knowledge of oscillation parameters
  unless
• SSM is improved
• (Weve learned a lot since these experiments
  were proposed)
• The measurement can improve the solar model,

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Other Future Measurements?

• Detection of pp neutrinos?
• Flux predicted to ?1
• Much higher flux, difficult to
• suppress backgrounds
• Several ideas under investigation
• LENS, HERON, MOON
• Neutrino superbeams?
• Brookhaven-to-Homestake proposal
• includes a possible signal, but its small

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Conclusions

• The combined results of a number of experiments
  have given
• us a clear picture of solar neutrino
  oscillations
• The solar neutrino deficit is due to ne flavor
  change
• The oscillation parameters are in the LMA region
• Mixing is non-maximal
• LMA I is strongly preferred
• The best measurement of tan2q will come from
  future SNO results
• The best measurement of Dm2 will come from
  future
• KamLAND reactor results
• Solar and reactor (neutrino and antineutrino)
  results will independently
• measure oscillation parameters
• Measurement of solar 7Be neutrinos will not
  improve our
• knowledge of mixing parameters
• It will take ambitious future experiments to
  make further