determining the neutrino mixing angle 13 with the daya bay nuclear power plants

Determining The Neutrino Mixing Angle 13 With The Daya Bay Nuclear Power

Plants

Kam-Biu Luk

University of California, Berkeley

andLawrence Berkeley National

Laboratory

Seminar at BNL, November 4, 2005

Kam-Biu Luk Daya Bay Experiment 2

Neutrino Mixing

Majorana phases

Six parameters: 2 m2, 3 angles, 1 phase + 2 Majorana phases

Pontecorvo-Maki-Nakagawa-Sakata Matrix

€

cosθ12 sinθ12 0

−sinθ12 cosθ12 0

0 0 1

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

cosθ13 0 sinθ13eiδ

0 1 0

−sinθ13eiδ 0 cosθ12

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

1 0 0

0 cosθ23 sinθ23

0 −sinθ23 cosθ23

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

1 0 0

0 e iδ1 0

0 0 e iδ 2

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

• For three generations of massive neutrino, the weak eigenstates are not the same as the mass eigenstates:

€

νe

νμ

ντ

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟=

Ue1 Ue2 Ue3

Uμ1 Uμ2 Uμ3

U τ1 U τ2 U τ3

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

ν1

ν2

ν3

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

solar ν reactor ν atmospheric ν neutrinolessreactor ν accelerator LBL ν accelerator LBL ν double- decay

• Parametrize the PMNS matrix as:

m12

m22

m32

m12

m22

m32

Normalhierarchy

Invertedhierarchy

m232

m221


Neutrino Oscillation

• The probability of νμ νe appearance is given by:

• The probability of νe X disappearance is:

€

P νe → X( ) ≈sin2 213 sin2 m312 L

4E

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟−cos4 13 sin2 212 sin2 m21

2 L

4E

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

€

P νμ → νe( ) ≈sin2 213 sin2 23 sin2 m312 L

4E

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

+ sin2 212 cos2 23 sin2 m212 L

4E

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

- (A ρ)cos2 13 sin13 sinδ


Current Status of Mixing Parameters

(23, m232)

(12, m221)

(13, m231)

m231 m2

32 >> m221

12 and 23 are large

Unknowns： sin2213 ， δ , sign of m2

32

m232 =(2.4+0.4

-0.3)10-3 eV2

23 45 m2

21 =(7.8+0.6-0.5)10-5 eV2

12 =(32+4-3)


Current Knowledge of 13

Maltoni etal., New J. Phys. 6,122(04)

Sin2(213) < 0.09

Sin2(213) < 0.18

At m231 = 2.5103 eV2,

sin2213 < 0.15


Some Ideas For Measuring 13

decay pipehorn absorbertargetp detector

+

+ μ+

Method 1: Accelerator Experiments

• appearance experiment:• need other mixing parameters to extract 13• baseline O(100-1000 km), matter effects present • expensive

Method 2: Reactor Experiments

• disappearance experiment: νe X• baseline O(1 km), no matter effects • relative cheap

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

€

ν μ → ν e

€

Pμe ≈sin2 213 sin2 223 sin2 m31

2L

4E ν

⎛

⎝

⎜ ⎜

⎞

⎠

⎟ ⎟+ ...

€

Pee ≈1−sin2 213 sin2 m31

2L

4E ν

⎛

⎝

⎜ ⎜

⎞

⎠

⎟ ⎟+ cos4 13 sin2 212 sin2 m21

2L

4E ν

⎛

⎝

⎜ ⎜

⎞

⎠

⎟ ⎟


Synergy of Reactor and Accelerator Experiments

Δm2 = 2.5×10-3 eV2 sin2213 = 0.05

Reactor experiments can help in Resolving the 23 degeneracy

(Example: sin2223 = 0.95 ± 0.01)

90% CL

Reactor w 100t (3 yrs) + Nova Nova only (3yr + 3yr) Reactor w 10t (3yrs) + Nova

90% CL

McConnel & Shaevitz, hep-ex/0409028

90% CL

Reactor w 100t (3 yrs) +T2K T2K (5yr,ν-only) Reactor w 10t (3 yrs)+T2K

Reactor experiments providea better determination of 13


Reactor νe

nXXnU 221

2 3 5

92+++

For 235U fission, for instance,

where X1 and X2 are stablenuclei e.g.

4094 Zr Ce140

58

yielding a total of 98protons, whereas 235U has 92protons. That is, on average, 6 neutrons must beta decay,giving 6 νes (per ~200 MeV).

νe/MeV/

fisson

3 GWth generates 6 × 1020 νe per sec


Detection of ν in liquid scintillator:Inverse Decay

ν

μ

νe p e+ + n (prompt)

+ p D + (2.2 MeV) (delayed by ~180 μs)

+ Gd Gd* + ’s(sum = 8 MeV) (delayed by ~30 μs)

Time-, space- and energy-tagged signal is a goodtool to suppress background events.

Energy of νe is given by:

Eν Te+ + Tn + (mn - mp) + m e+ Te+ + 1.8 MeV 10-40 keV

Threshold of inverse decay is about 1.8 MeV; thus only about 25%of the reactor νe is usable.


σ(E) =0.0952Eepe

1MeV2⎛ ⎝ ⎜ ⎞

⎠ ⎟ ×10−42cm2P(ν e → ν e)=1

- 42


How To Measure 13 With Reactor νe?

0

2

4

6

8

10

0 2 4 6 8 10

Energy of ν ( )MeV

0.05 Number of Events per MeV

= 2 L km

sin2213 = 1

No oscillation

m231 = 0.0025 eV2

1. Rate deficit: deviation from 1/r2 expectation2. Spectral distortion


Time Variation of Fuel Composition

Typically known to ~1%

235U

238U239Pu

241Punormalized flux times cross section (arbitrary units)

0 0.5 1 1.5 2 2.5 3 3.5

1 2 3 4 5 6 7 8 9 10E (MeV)


Uncertainty in νe Energy Spectrum • Three ways to obtain the energy spectrum:

– Direct measurement– First principle calculation– Sum up anti-neutrino spectra from 235U,

239Pu, 241Pu and 238U 235U, 239Pu, 241Pu from their measured

spectra 238U(10%) from calculation (10%)

• Measurements agree with calculations to ~2%

Gö

sg

en

Bugey3 Measurement Best calculation

Bugey3 Measurementfirst-principle calculation


Background

12B12N

Depends on theflux of cosmicmuons in thevicinity of thedetector

Go as deepas possible!

Keep everything as radioactively pure as possible!

KamLAND


Location of Daya Bay

• 45 km from Shenzhen

• 55 km from Hong Kong


LingAo II NPP:2 2.9 GWth

Ready by 2010

The Site

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Daya Bay NPP:2 2.9 GWth

LingAo NPP:2 2.9 GWth


Ranking of Nuclear Power Plants

0 2 4 6 8 10 12 14 16 18 20 22 24 26 GWth

1. Kashiwazaki (Japan) (7)

2. Zaporozhye (Ukraine) (6)

5. Gravelines (France) (6)

6. Paluel (France) (4)

6. Cattenom (France) (4)

9. Hamaoka (Japan) (5)

11. Fukushima Daini (Japan) (4)10. Ohi (Japan) (4)

8. Fukushima Daiichi (Japan) (6)

3. Yonggwang (S. Korea) (6)3. Ulchin (S. Korea) (6)

12. Daya Bay-Ling Ao (China) (4+2)~2010


Horizontal Access Tunnels

• Advantages of horizontal access tunnel:

- mature and relatively inexpensive technology

- flexible in choosing overburden

- relatively easy and cheap to add expt. halls

- easy access to underground experimental facilities

- easy to move detectors between different

locations with good environmental control.




A ~1.5 km-long Tunnel Onsite


Cross Section of Tunnel For Daya Bay Experiment

1.2 m1.2 m7.2 m

0.8 m

3.2 m 3.2 m


0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0.1 1 10 100

Nosc

/N

no_osc

Baseline (km)

Sin2(213) = 0.1m2

31 = 2.5 x 10-3 eV2

Sin2(212) = 0.825m2

21 = 8.2 x 10-5 eV2

Where To Place The Detectors ?

reactor near detector to measure raw flux at L1

far detector to measurechanges at L2

νe


Where To Place The Detectors At Daya Bay?

Daya Bay

Ling Ao~1700 m


Daya BayNPP

Ling AoNPP

Daya BayNear

Ling AoNear

Far site

Ling Ao-ll NPP(under const.)

590 m

1175 m 570 m

Possible Locations of Detector SitesEmpty detectors are moved to underground halls through an access tunnel with 8% slope.Filled detectors can be swapped between the underground halls via the 0%-slope tunnels.

Excessportal




Location ofTunnel Entrance

Entrance portal




Location of Daya Near Detector




Location of Ling Ao Near Detector




Location of Far Detector


A Versatile Site• Rapid deployment:

- Daya near site + mid site - 0.7% reactor systematic error

• Full operation: (1) Two near sites + Far site (2) Mid site + Far site (3) Two near sites + Mid site + Far site Internal checks, each with different systematic


What Target Mass Should Be?

Systematic error (per site): Black : 0.6% Red : 0.25% Blue : 0.12%

Solid lines : near+farDashed lines : mid+far

DYB: B/S = 0.5% LA: B/S = 0.4% Mid: B/S = 0.1% Far: B/S = 0.1%

m231 = 2 10-3 eV2


Conceptual Design of Detector Modules

• Three-layer structure: I. Target: Gd-loaded liquid

scintillatorII. Gamma catcher: liquid

scintillator, 45cmIII. Buffer shielding: mineral oil,

~45cm • Possibly with diffuse reflection

at ends. For ~200 PMT’s around the

barrel:

vertex

14%~ , 14cm

(MeV)=

E Eσ σ

buffer

20t

Gd-doped

LS

gamma catcher

40 t


~350 m

~97 m

~98 m~208 m

Cosmic-ray Muon• Apply the Geiser parametrization for cosmic-ray flux at surface• Use MUSIC and mountain profile to estimate muon flux & energy

DYB LingAo

Mid Far

Elevation (m) 97 98 208 347

Flux (Hz/m2) 1.2 0.94 0.17 0.045

Mean Energy (GeV)

55 55 97 136

near site

far site


Conceptual Design of Shield-Muon Veto

• Detector modules enclosed by 2m+ of water to shield neutrons and gamma-rays from surrounding rock• Water shield also serves as a Cherenkov veto• Augmented with a muon tracker: scintillator strips or RPCs• Combined efficiency of Cherenkov and tracker > 99.5%

detectormodule

PMTsTracker

rock


Alternative Design

40t-3 layermodule

top ofwater pool


Background Inside Detector

Two classes of background:

1. Uncorrelated:

Accidental ─ random coincidence of two unrelated events appear close in space and time.

2. Correlated::

Fast neutron ─ a fast spallation neutron gets into the detector, creates a prompt signal (knock-out proton), thermalizes and is captured.

CosmogenicCosmogenic isotopes isotopes ─ 9Li and 8He with β-n decay modes are created in spallation of μ with 12C. Thedecays mimic the antineutrino signal.


-n Decay Of 8He And 9Li

Correlated final state: Correlated final state: ββ+n+2+n+2αα

Correlated final state: Correlated final state: ββ+n++n+77LiLi

τ½ = 178 ms 49.5% Correlated

τ½ = 119 ms 16%

Correlated


Background

Near Site

Far Site

Radioactivity (Hz) <50 <50Accidental B/S <0.05% <0.05%

Fast Neutron background B/S

0.15% 0.1%

8He/9Li B/S 0.55% 0.25%

• Use a modified Palo-Verde-Geant3-based MC to model response of detector.

• Cosmogenic isotopes: 8He/9Li which can -n decay - Cross section measured at CERN (Hagner et. al.)

- Can be measured in-situ, even for near detector with muon rate ~ 10 Hz.

The above number is before shower-muon cutwhich can further reduce cosmogenic background.

20t moduleQuickTime™ and a

TIFF (LZW) decompressorare needed to see this picture.


Detector Systematic Issues

Potential sources of systematic uncertainty are:

• detector efficiency • gadolinium fraction (neutron detection efficiency)• target mass• target chemistry: fraction of free proton (target particle) in terms of hydrogen/carbon• trigger efficiency• cut efficiency• live time• surprises at the 0.01 level


Possible Solutions

• Relative detector efficiency Calibrate all detectors with the same set of radioactive sources.

• Gd fraction (i) Control synthesis of liquid scintillator (ii) Measure the Gd- to H-capture ratio

• Target mass(i) Use the same batch or equally splitting batches of liquid scintillator, and measure flow rates(ii) Use νe events to cross calibrate, implying moving detectors.


Detector Systematic Uncertainties

permodule

absolute measurementsrelative

measurement

0.10.1

0.1

0.25%


• Topography survey: Completed• Geological Survey: Completed

• Verified topographic information• Generated new map covering 7.5 km2

• Geological Physical Survey: Completed• High-resolution electric resistance• Seismic • Micro-gravity

• Bore-Hole Drilling: November-December, 2005

Geotechnical Survey

raw data


Daya BayNPP

Ling AoNPP

Daya Bay Near360 m from Daya BayOverburden: 97 m

Far site1600 m from Lingao1900 m from DayaOverburden: 350 m

Ling Ao-ll NPP(under const.)

8% slope

672 m(12% slope)

Ling Ao Near500 m from LingaoOverburden: 98 m

Mid site~1000 m from DayaOverburden: 208 m

Total length: ~3200 m


• Daya Bay site Daya Bay site - baseline = 360 m- baseline = 360 m

- target mass = 40 ton- target mass = 40 ton

- B/S = ~0.5%- B/S = ~0.5%

• LingAo site LingAo site - baseline = 500 m- baseline = 500 m


- B/S = ~0.5%- B/S = ~0.5%

• Far site Far site - baseline = 1900 m to DYB - baseline = 1900 m to DYB

corescores

1600 m 1600 m to LA coresto LA cores


- B/S = ~0.2%- B/S = ~0.2%

• Three-year run (0.2% Three-year run (0.2% statistical error)statistical error)

• Detector residual error = Detector residual error = 0.2%0.2%

• Use rate and spectral Use rate and spectral shapeshape

90% confidence level90% confidence level

Sensitivity of sin2213

Sept, 2005

2 near + far

near (40t) + mid (40 t)

1 year


Precision of m231

sin2213 = 0.02

sin2213 = 0.1


Gd-loaded Liquid Scintillator

• It can significantly reduce backgrounds

(short capture time, high capture energy)

• Problems:

(a) doping Gd into organic LS from inorganic

Gd compound and achieve Light yield = 55% of

anthracene Att. length = 11m

(b) Aging Palo Verde: 0.03%/day Chooz: 0.4%/day


Synthesis of Gd-loaded Liquid Scintillator• Investigating a few candidates at IHEP:

Date 2005.

06.13

2005.

08.01

2005.

08.26

Gd (%) 0.1 0.098 0.1

One candidate:

- 0.1% Gd (D2EHP-ligand) in

20% mesitylene-80% dodecane

- Light yield: 91% of pure LS

- attenuation length = 6.2 m

- stable for more than two months:

- no effect on acrylic

• R&D collaborative effort at BNL: - Gd (carboxylate ligands) in PC and dodecane - all stable for almost a year


Prototype Detector at IHEP• Constructing a 2-layer prototype with

0.5 t Gd-doped LS enclosed in 5 t of

mineral oil, and 45 8” PMTs to evaluate

design issues at IHEP, Beijing

Steel tank

acrylic vessel

PMT mount

Front-end board (version 2)


Installing proptubes in Sept, 2005

The Aberdeen Tunnel Experiment• Study cosmic muons & cosmogenic background in Aberdeen Tunnel, Hong Kong.

similar geologybetween Aberdeen and Daya Bay

Overburden ~Daya Bay sites


Precision Measurement of 12 and m221


Precise Measurement of 12

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0.1 1 10 100

Nosc

/N

no_osc

Baseline (km)

Large-amplitude oscillation at ~55 km

due to 12

• Near detectors close to reactors measure raw flux and spectrum of νe, reducing reactor-related systematic

• Position a far detector near the first oscillation maximum to get the highest sensitivity of 12

Sin2(213) = 0.1m2

31 = 2.5 x 10-3 eV2

Sin2(212) = 0.825m2

21 = 8.2 x 10-5 eV2

• Since reactor νe are low-energy, it is a disappearance experiment:

KamLAND



are needed to see this picture.Tai Mo Shan(957 m)

~55 km

Daya BayNPP

Hong Kong

Shenzhen

Location of Hong Kong Site For 12 Measurement


Precision of 12 With The Daya Bay Facility

Inputs:• Thermal power = 17.4 GW• Baseline = 55 km• Target mass = ~ 500 ton LS• Mixing parameters:

sin2212 = 0.825

sin2213 = 0.1

m212 = 8.2 10-5 eV2

m213 = 2.5 10-3 eV2


Summary and Prospects• The Daya Bay nuclear power facility in China and the mountainous

topology in the vicinity offer an excellent opportunity for carrying out a reactor neutrino program using horizontal tunnels.

• The Daya Bay experiment has excellent potential to reach a sensitivity of 0.01 for sin2213.

• The three Chinese funding agencies are discussing cost-sharing of a request of RMB$200 million.

• The US team is waiting for the NuSAG’s decision.

• Will complete detailed design of detectors, tunnels and underground facilities in 2006.

• Plan to commission the Fast Deployment scheme in 2007-2008, and Full Operation in 2009.

• Welcome more collaborators to join.


What Have We Learned From Chooz?

CHOOZ Systematic Uncertainties

Reactor ν flux & spectrumDetector Acceptance

2%1.5%

Total 2.7%

5 t Gd-loaded liquid scintillatorto detect

L = 1.05 km

D = 300 mwe

P = 8.4 GWthRate: ~5 evts/day/t (full power) including 0.2-0.4 bkg/day/t

νe + p e+ + n

e+ + e- 2 x 0.511 MeV n + Gd 8 MeV of s; τ ~ 30 μs

~3000 νe candidates(included 10% bkg) in335 days

determining the neutrino mixing angle 13 with the daya bay nuclear power plants

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