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

Measuring sin2213 with the Daya Bay nuclear power reactors

• Yifang Wang

• Institute of High Energy Physics

Neutrinos

• 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

• CHOOZ

• 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 :

• Two tracker options :

• RPC outside the steel cylinder
• Scintillator Strips sink into the water

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

Summary

• 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