Neutrino mass hierarchy and ?13 Determination by Remote Detection of Reactor Antineutrinos

1
Neutrino mass hierarchy and ?13 Determination by
Remote Detection of Reactor Antineutrinos

• Mikhail Batygov,
• On behalf of UH Hanohano group,
• September 14, Sendai TAUP 2007

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Outline

• Neutrino oscillation parameters
• Current knowledge
• Parameters to be estimated at higher accuracy
• Methods
• Requirements and the Hanohano project
• Other physics goals
• Current status and conclusion

3
Oscillation Parameters present

• KamLAND (with SNO) analysis
• tan2(?12)0.40(0.10/0.07)
• ?m221(7.90.4/-0.35)10-5 eV2
• Araki et al., Phys. Rev. Lett. 94 (2005) 081801.
  
• (UPDATED talk by I. Shimizu at this conference)
• SuperK and K2K
• ?m231(2.50.5)10-3 eV2
• Ashie et al., Phys. Rev. D64 (2005) 112005
• Aliu et al., Phys. Rev. Lett. 94 (2005) 081802
• CHOOZ limit sin2(2?13) 0.20
• Apollonio et al., Eur. Phys. J. C27 (2003)
  331-374.

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Oscillation parameters to be measured
2 mass diffs, 3 angles, 1 CP phase

• Precision measurement
• of mixing parameters needed
• World effort to determine ?13 ( ?31)
• Determination of mass hierarchy

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3-? mixing

• Pee1- cos4(?13) sin2(2?12) 1-cos(?m212L/2E)
• cos2(?12) sin2(2?13)
  1-cos(?m213L/2E)
• sin2(?12) sin2(2?13)
  1-cos(?m223L/2E)/2
• Survival probability 3 oscillating terms each
  cycling in L/E space (t) with own periodicity
  (?m2?)
• Amplitude ratios 13.5 2.5 1.0
• Oscillation lengths 110 km (?m212) and 4 km
  (?m213 ?m223) at reactor peak 3.5 MeV
• Two possible approaches
• ½-cycle measurements can yield
• Mixing angles, mass-squared differences
• Less statistical uncertainty for same parameter
  and detector
• Multi-cycle measurements can yield
• Mixing angles, precise mass-squared differences
• Mass hierarchy
• Less sensitivity to systematic errors

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?12 precise measurement

• Reactor experiment- ? e point source
• P(?e??e)1-sin2(2?12)sin2(?m221L/4E)
• 60 GWkty exposure at 50-70 km
• 4 systematic error
• from near detector
• sin2(?12) measured with
• 2 uncertainty

Ideal spot
Bandyopadhyay et al., Phys. Rev. D67 (2003)
113011. Minakata et al., hep-ph/0407326 Bandyopadh
yay et al., hep-ph/0410283
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3-flavor oscillations

• High-frequency amplitude is ?13
• In L/E plot, a purely sinusoidal factor
• Invites the use of Fourier Transform for analysis

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Fourier Transformed Spectrum

• The size of the peak proportional to ?13.
• The peaks asymmetry tells about hierarchy
• Method developed at UH

?m232 lt ?m231 normal hierarchy
0.0025 eV2 peak due to nonzero ?13
Preliminary- 50 kt-y exposure at 50 km
range sin2(2?13)0.02 ?m2310.0025 eV2 to 1
level Learned, Dye,Pakvasa, Svoboda
hep-ex/0612022
Includes energy smearing
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Hierarchy Discrimination
Perfect E resolution
?E 6sqrt(Evis)
E?, MeV
E?, MeV

• Uses the difference in spectra
• Efficiency depends heavily on energy resolution

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Estimation of the statistical significance
Neutrino events to 1 ? CL
lt 3 desirable but maybe unrealistic E resolution
KamLAND 0.065 MeV0.5
Detector energy resolution, MeV0.5

• Thousands of events necessary for reliable
  discrimination, even at 1 ? CL
• Longer baselines more sensitive to energy
  resolution may be beneficial to adjust for
  actual detector performance

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Additional goal neutrino geophysics

• Antineutrinos produced in ?-decays of 232Th and
  238U decay series isotopes
• A substantial (but not known precisely) part of
  Earth heat flux of 40 (31) TW
• In continent-based detectors, flux dominated by
  continental crust
• Ocean-based detectors allow to measure
  geo-neutrino flux from mantle

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Requirements

• Baseline on the order of 50 km better variable
  for different studies
• Big number of events (large detector)
• For Hierarchy
• Good to excellent energy resolution
• sin2(2?13) ? 0
• No full or nearly full mixing in ?12 (almost
  assured by SNO and KamLAND)
• For Geo-neutrinos ability to switch off
  reactor background

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MeV-Scale Electron Anti-Neutrino Detection
Key 2 flashes, close in space and time, 2nd of
known energy, eliminate background
Production in reactors and natural decays
Detection
EvisE?-0.8 MeV prompt
delayed Evis2.2 MeV

• Standard inverse ß-decay coincidence
• E? gt 1.8 MeV
• Rate and precise spectrum but no direction

Reines Cowan
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Hanohano detector

• 10-kt LS detector
• Primary detection method inverse-beta decay
• Ocean-based, with 2 key advantages
• Adjustable baseline
• Ability to avoid reactor background in the
  geo-neutrino studies

Barge 112 m long x 23.3 wide
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Additional Physics/AstrophysicsHanohano will be
biggest low energy neutrino detector

• Nucleon Decay (SUSY-favored kaon modes may be
  also possible)
• Supernova Detection special ?e ability
• Relic SN Neutrinos
• GRBs and other rare impulsive sources
• Long list of ancillary, non-interfering science,
  with strong discovery potential

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Current status

• Several workshops held (04, 05, 06) and ideas
  developed
• Study funds provided preliminary engineering and
  physics feasibility report (11/06)
• Strongly growing interest in geology community
• Work proceeding and collaboration in formation
• Upcoming workshops in Washington DC (10/07) and
  Paris (12/07) for reactor monitoring
• Funding request for next stage (06) in motion
• Ancillary proposals and computer studies continue

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Summary

• Better precision for sin2(2?12) and sin2(2?13)
  along with the determination of hierarchy
  possible for reactor-based antineutrino
  experiment
• Variable baseline desirable
• particular measurements require individual tuning
• optimal placement dependent on unknown parameters
• minimize systematic errors (esp. in energy scale)
  
• Needs large statistics ? big detector
• Requires precise ?e energy measurement
• Hanohano designed to meet those goals and also
  provides
• Unique sensitivity to mantle geo-neutrinos
• Ability to avoid reactor background when needed
• Additional physics measurements achievable to
  higher precision