Measuring sin2213 with the Daya Bay nuclear power reactors Yifang Wang

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Measuring sin2213 with the Daya Bay nuclear power reactors

  • Yifang Wang

  • Institute of High Energy Physics


  • Basic building blocks of matter:

  • Tiny mass, neutral, almost no interaction with matter, very difficult to detect.

  • Enormous amount in the universe, ~ 100/cm3 , about 0.3% -1% of the total mass of the universe

  • Most of particle and nuclear reactions produce neutrinos: particle and nuclear decays, fission reactors, fusion sun, supernova, -burst,cosmic-rays ……

  • Important in the weak interactions: P violation from left-handed neutrinos

  • Important to the formation of the large structure of the universe, may explain why there is no anti-matter in the universe

Brief history of neutrinos

Neutrino oscillation: PMNS matrix

A total of six  mixing parameters:

  • at reactors:

  • Pee  1  sin22sin2 (1.27m2L/E) 

  • cos4sin22sin2 (1.27m2L/E)

  • at LBL accelerators:

  • Pe ≈ sin2sin22sin2(1.27m2L/E) +

  • cos2sin22sin2(1.27m212L/E) 

  • A()cos213sinsin()

Why at reactors

  • Clean signal, no cross talk with  and matter effects

  • Relatively cheap compare to accelerator based experiments

  • Can be very quick

  • Provides the direction

  • to the future of

  • neutrino physics

  • No good reason(symmetry) for sin2213 =0

  • Even if sin2213 =0 at tree level, sin2213 will not vanish at low energies with radiative corrections

  • Theoretical models predict sin2213 ~ 0.1-10 %

Importance to know 13

  • 1)A fundamental parameter

  • 2)important to understand the relation between leptons and quarks, in order to have a grand unified theory beyond the Standard Model

  • 3)important to understand matter-antimatter asymmetry

    • If sin22,next generation LBL experiment for CP
    • If sin22next generation LBL experiment for CP ???
  • 4)provide direction to the future of the neutrino physics: super-neutrino beams or neutrino factory ?

Recommendation of APS study report:

How to do this experiment

How Neutrinos are produced in reactors ?

Fission rate evolution with time in the Reactor

Neutrino energy spectrum

  • K. Schreckenbach et al., PLB160,325

  • A.A. Hahn, et al., PLB218,365

Reactor thermal power

Prediction of reactor neutrino spectrum

  • Three ways to obtain reactor neutrino spectrum:

    • Direct measurement
    • First principle calculation
    • Sum up neutrino spectra from 235U, 239Pu, 241Pu and 238U
    • 235U, 239Pu, 241Pu from their measured  spectra
    • 238U(10%) from calculation (10%)
  • They all agree well within 3%

Reactor Experiment: comparing observed/expected neutrinos:

  • Palo Verde


  • KamLAND

How to reach 1% precision ?

  • Three main types of errors: reactor related(~2-3%), background related (~1-2%) and detector related(~1-2%)

  • Use far/near detector to cancel reactor errors

  • Movable detectors, near far, to cancel part of detector systematic errors

  • Optimize baseline to have best sensitivity and reduce reactor related errors

  • Sufficient shielding to reduce backgrounds

  • Comprehensive calibration to reduce detector systematic errors

  • Careful design of the detector to reduce detector systematic errors

  • Large detector to reduce statistical errors

Systematic error comparison

Currently Proposed experiments

Daya Bay nuclear power plant

  • 4 reactor cores, 11.6 GW

  • 2 more cores in 2011, 5.8 GW

  • Mountains near by, easy to construct a lab with enough overburden to shield cosmic-ray backgrounds

Convenient Transportation, Living conditions, communications

Cosmic-muons at sea level: modified Gaisser formula

Cosmic-muons at the laboratory

Baseline optimization and site selection

  • Neutrino spectrum and their error

  • Neutrino statistical error

  • Reactor residual error

  • Estimated detector systematical error:

  • total, bin-to-bin

  • Cosmic-rays induced background

  • (rate and shape) taking into mountain

  • shape: fast neutrons, 9Li, …

  • Backgrounds from rocks and PMT glass

Best location for far detectors

Geologic survey completed, including boreholes

Site investigation completed

Engineering Geological Map

Tunnel construction

  • The tunnel length is about 3000m

  • Local railway construction company has a lot of experience (similar cross section)

  • Cost estimate by professionals, ~ 3K $/m

  • Construction time is ~ 15-24 months

  • A similar tunnel on site as a reference

How large the detector should be ?

Detector: Multiple modules

  • Multiple modules for cross check, reduce uncorrelated errors

  • Small modules for easy construction, moving, handing, …

  • Small modules for less sensitive to scintillator aging

  • Scalable

Central Detector modules

  • Three zones modular structure:

    • I. target: Gd-loaded scintillator
    • -ray catcher: normal scintillator
    • III. Buffer shielding: oil
  • Reflection at two ends

  • 20t target mass, ~200 8”PMT/module

  • E = 5%@8MeV, s ~ 14 cm

Water Buffer & VETO

  • 2m water buffer to shield backgrounds from neutrons and ’s from lab walls

  • Cosmic-muon VETO Requirement:

    • Inefficiency < 0.5%
    • known to <0.25%
  • Solution: Two active vetos

    • active water buffer, Eff.>95%
    • Muon tracker, Eff. > 90%
      • RPC
      • scintillator strips
    • total ineff. = 10%*5% = 0.5%

Two tracker options :

Background related error

  • Need enough shielding and an active veto

  • How much is enough ?  error < 0.2%

    • Uncorrelated backgrounds: U/Th/K/Rn/neutron
    • single gamma rate @ 0.9MeV < 50Hz
    • single neutron rate < 1000/day
    • 2m water + 50 cm oil shielding
    • Correlated backgrounds: n  E0.75
      • Neutrons: >100 MWE + 2m water
      • Y.F. Wang et al., PRD64(2001)0013012
      • 8He/9Li: > 250 MWE(near) &
      • >1000 MWE(far)
      • T. Hagner et al., Astroparticle. Phys.
      • 14(2000) 33

Background estimated by GEANT MC simulation

Sensitivity to Sin2213

  • Reactor-related correlated error: c ~ 2%

  • Reactor-related uncorrelated error: r ~ 1-2%

  • Calculated neutrino spectrum shape error: shape ~ 2%

  • Detector-related correlated error: D ~ 1-2%

  • Detector-related uncorrelated error: d ~ 0.5%

  • Background-related error:

  • fast neutrons: f ~ 100%,

  • accidentals: n ~ 100%,

  • isotopes(8Li, 9He, …) : s ~ 50-60%

  • Bin-to-bin error: b2b ~ 0.5%

Sensitivity to Sin2213

Development of Gd-loaded LS

Aberdeen tunnel in HK:

  • background measurement

Status of the project

  • CAS officially approved the project

  • Chinese Atomic Energy Agency and the Daya Bay nuclear power plant are very supportive to the project

  • Funding agencies in China are supportive, R&D funding in China approved and available

  • R&D funding from DOE approved

  • Site survey including bore holes completed

  • R&D started in collaborating institutions, the prototype is operational

  • Proposals to governments under preparation

  • Good collaboration among China, US and other countries

Schedule of the project

  • Schedule

    • 2004-2006 R&D, engineering design,
    • secure funding
    • 2007-2008 proposal, construction
    • 2009 installation
    • 2010 running


  • Knowing Sin2213 to 1% level is crucial for the future of neutrino physics, particularly for the leptonic CP violation

  • Reactor experiments to measure Sin2213 to the desired precision are feasible in the near future

  • Daya Bay NPP is an ideal site for such an experiment

  • A preliminary design is ready, R&D work is going on well, proposal under preparation

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