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Daya Bay Reactor Neutrino Oscillation Experiment

Jen-Chieh Peng

International Workshop on “Double Beta Decay and Neutrinos” Osaka, Japan,

June 11-13, 2007

University of Illinois at Urbana-Champaign

(on behalf of the Daya Bay Collaboration)

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Outline

13 Physics case for a precise measurement

The proposed Daya Bay neutrino oscillation

experiment

Schedule and expected sensitivity of the

Daya Bay experiment

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What we have learned from neutrino oscillation experiments

2 2 2 5 221 2 1

2 2 2 3 232 3 2

e 12 13 12 13 13

12 23 12 2

(7.9 0.7) 10 ev (90%c.l.)

| | | | (2.4 0.6) 10

1) Neutrinos are massive

2) Neutrinos do mix with each ot

ev (90% )

e

c.l.

h ri

m m m

m m m

c c s c s e

s c c s

1

3 13 12 23 12 23 13 23 13 2

12 23 12 23 13 12 23 12 23 13 23 13 3

12 23 3

3 1

1

12 2 3

( cos , sin )

13 , 2.

34 , 45 , 13 for the l

2 , 0

epton MNSP Matrix

i i

i i

ij ij ij ij

s e c c s s s e s c

s s c c s e c s s c s e c c

c s

3) Neutrino masses and mixings have provided clear evidence for

physic

.22 for the quark C

s beyond the Stand

KM Matrix

ard Model

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What we do not know about the neutrinos

• Dirac or Majorana neutrinos?

• Mass hierachy and values of the masses?

• Existence of sterile neutrinos?

• Value of the θ13 mixing angle?

• Values of CP-violation phases?

• Origins of the neutrino masses?

• Other unknown unknowns …..

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What we know and do not know about the neutrinos

e 12 13 12 13 1

12 23 12 23 12 23 12 23 23 13 2

12 23 12 23 12 23

13

13

12 23 23 1

3

3

1

13 13 3

i

i i

i i

s e

s e s e

s

c c s c

s c c s c c s s s c

s s c c c se sc ces c

• What is the νe fraction of ν3? (proportional to sin2θ13)

• Contributions from the CP-phase δ to the flavor compositions of neutrino mass eigenstates depend on sin2θ13)

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Why measuring θ13?

A measurement of sin22θ13 at the sensitivity level of 0.01 can rule out at least half of the models!

• Models based on the Grand Unified Theories in general give relatively large θ13

• Models based on leptonic symmetries predict small θ13

A recent tabulation of predictions of 63 neutrino mass models on sin2θ13

(hep-ph/0608137)

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Why measuring θ13?

A measurement of sin22θ13 AND the mass hierarchy can rule out even more models!

A recent tabulation of predictions of 63 neutrino mass models on sin2θ13

(hep-ph/0608137)

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Why measuring θ13? Leptonic CP violation

212 12 13 13 23 23

2 2213 2312

( ) ( ) 16

sin sin sin sin4 4 4

e eP P s c s c s c

m mmL L L

E E E

If sin22θ13 > 0.02-0.03, then NOvA+T2K will have good coverage on CP δ.

Size of sin22θ13 sets the scale for future leptonic CP violation studies

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Current Knowledge of 13

Direct search

At m231 = 2.5 103 eV2,

sin22 < 0.17

allowed region

Fogli etal., hep-ph/0506083

Global fit

sin2213 < 0.11 (90% CL)

Best fit value of m232 = 2.4 103

eV2

sin2213 = 0.04

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decay pipehorn absorbertargetp detector

+

+ +

Method 1: Accelerator Experiments

Method 2: Reactor Experiments

Pe sin2 213sin2 223sin2 m31

2L

4E

...

Pee 1 sin2 213sin2 m31

2L

4E

cos4 13sin2 212sin2 m21

2L

4E

• e X disappearance experiment• baseline O(1 km), no matter effect, no ambiguity • relatively cheap

• e appearance experiment• need other mixing parameters to extract 13

• baseline O(100-1000 km), matter effects present • expensive

Some Methods For Determining 13

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Detecting : Inverse Decay

e p e+ + n (prompt)

+ p D + (2.2 MeV) (delayed) + Gd Gd*

Gd + ’s(8 MeV) (delayed)

• Time- and energy-tagged signal is a good tool to suppress background events.

• Energy of e is given by:

E Te+ + Tn + (mn - mp) + m e+ Te+ + 1.8

MeV 10-40 keV

• The reaction is the inverse -decay in 0.1% Gd-doped liquid scintillator:

Arb

itra

ry

Flux Cross

Sectio

n

Observable Spectrum

From Bemporad, Gratta and Vogel

0.3b

50,000b

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Measuring 13 with Reactor NeutrinosSearch for 13 in new oscillation experiment

~1-1.8 km

> 0.1 km

24 2 2 21

13

22 2 31

13 12cos sin 2sin 2 si sin4

1 n4ee

m L

E

mP

L

E

13

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0.1 1 10 100

Nos

c/Nn

o_os

c

Baseline (km)

Large-amplitudeoscillation due to 12

Small-amplitude oscillation due to 13 integrated over E

m213≈ m2

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detector 1 detector 2

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Results from Chooz

5-ton 0.1% Gd-loaded liquid scintillatorto detect e + p e+ + n

L = 1.05 km

D = 300 mwe

P = 8.4 GWth

Rate: ~5 evts/day/ton (full power) including 0.2-0.4 bkg/day/ton

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

Systematic uncertainties

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• Increase statistics:– Use more powerful nuclear reactors

– Utilize larger target mass, hence larger detectors

• Suppress background:– Go deeper underground to gain overburden for reducing cosmogenic background

• Reduce systematic uncertainties:– Reactor-related:

• Optimize baseline for best sensitivity and smaller reactor-related errors

• Near and far detectors to minimize reactor-related errors– Detector-related:

• Use “Identical” pairs of detectors to do relative measurement

• Comprehensive program in calibration/monitoring of detectors

• Interchange near and far detectors (optional)

How to Reach a Precision of 0.01 in sin2213?

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World of Proposed Reactor Neutrino Experiments

Angra, Brazil

Diablo Canyon, USA

Braidwood, USAChooz, France Krasnoyasrk, Russia

Kashiwazaki, Japan

RENO, Korea

Daya Bay, China

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Location of Daya Bay• 45 km from Shenzhen

• 55 km from Hong Kong

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Ling Ao II NPP:2 2.9 GWth

Ready by 2010-2011

Ling Ao NPP:2 2.9 GWth

Daya Bay NPP:2 2.9 GWth

1 GWth generates 2 × 1020 e per sec

The Daya Bay Nuclear Power Complex• 12th most powerful in the world (11.6 GWth)• Fifth most powerful by 2011 (17.4 GWth)• Adjacent to mountain, easy to construct tunnels to reach underground labs with sufficient overburden to suppress cosmic rays

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Daya BayNPP

Ling AoNPP

Ling Ao-ll NPP(under const.)

Empty detectors: moved to underground halls through access tunnel.Filled detectors: transported between underground halls via horizontal tunnels.

Total length: ~3100 m

295 m

81

0 m

465 m

900 m

Daya Bay Near363 m from Daya BayOverburden: 98 m

Ling Ao Near~500 m from Ling AoOverburden: 112 m

Far site1615 m from Ling Ao1985 m from DayaOverburden: 350 m

entrance

Filling hall

Mid site 873 m from Ling Ao1156 m from DayaOverburden: 208 m

Constructiontunnel

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Conceptual design of the tunnel and the Site investigation including bore holes completed

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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

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Antineutrino Detectors• Three-zone cylindrical detector design

– Target zone, gamma catcher zone (liquid scintillator), buffer zone (mineral oil)– Gamma catcher detects gamma rays that leak out

• 0.1% Gd-loaded liquid scintillator as target material

– Short capture time and high released energy from capture, good for suppressing background

• Eight ‘identical’ detector modules, each with 20 ton target mass

– ‘Identical’ modules help to reduce detector-related systematic uncertainties

– Modules can cross check the performance of each other when they are brought to the same location

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BNL Gd-LS Optical Attenuation: Stable So Far ~700 days- Gd-carboxylate in PC-based LS stable for ~2 years. - Attenuation Length >15m (for abs < 0.003).- Promising data for Linear Alkyl Benzene, LAB (LAB use suggested by SNO+ experiment).

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Detector Prototype at IHEP• 0.5 ton prototype

(currently unloaded liquid scintillator)• 45 8” EMI 9350 PMTs:

14% effective photocathode coverage with top/bottom reflectors

• ~240 photoelectron per MeV :

9%/E(MeV)

prototype detector at IHEP

En

erg

y R

eso

lutio

n

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Background Sources1. Natural Radioactivity: PMT glass, steel, rock, radon in the air, etc

2. Slow and fast neutrons produced in rock & shield by cosmic muons

3. Muon-induced cosmogenic isotopes: 8He/9Li which can -n decay

- Cross section measured at CERN (Hagner et. al.)

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

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355 m

98 m

112 m208 m

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

DY

B

Ling

Ao

Mid Far

Overburden (m) 98 112 208 355

Muon intensity

(Hz/m2)

1.16 0.73 0.17 0.041

Mean Energy (GeV) 55 60 97 138

Daya BayLing Ao

Far

Mid

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Muon System

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Water Shield• Pool around the central detectors - 2.5m water in all directions.

• Side, bottom & AD surfaces are reflective (Tyvek or equivalent)

• Outer shield is optically separated 1m of water abutting sides and bottom of pool– PMT coverage ~1/6m2 on bottom and on two surfaces of side sections

• Inner shield has 1.5m water buffer for AD’s in all directions but up, there the shield is 2.5m thick– 8” PMTs 1 per 4m2 along sides and bottom - 0.8% coverage

Far Hall

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Muon System Active Components

• Inner water shield– 415 8” PMTs

• Outer water shield

– 548 8” PMTs

• RPCs– 756 2m 2m chambers in 189 modules– 6048 readout strips

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Summary of Systematic Uncertainties

sources Uncertainty

Reactors 0.087% (4 cores)

0.13% (6 cores)

Detector

(per module)

0.38% (baseline)

0.18% (goal)

Backgrounds 0.32% (Daya Bay near)

0.22% (Ling Ao near)

0.22% (far)

Signal statistics 0.2%

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34(hep-ex/0701029)

Daya Bay Conceptual Design Report