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2nd Sino-French Workshop on the Dark Universe

Changgen Yang

Institute of High Energy Physics, Beijing

for the Daya Bay Collaboration

Daya Bay Reactor Neutrino Experiment

The 4th International Conference on Flavor Physics, Sept 24-28, 2007, Beijing

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Outline • Physics Motivation • Requirements• The Daya Bay Experiment

– Layout– Detector (AD and Muon system) Design– Backgrounds– Systematic Errors and Sensitivity

• Site Survey• Civil Construction• Summary

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13The Last Unknown

Neutrino Mixing Angle UMNSP Matrix

U Ue1 Ue2 Ue3

U1 U2 U 3

U1 U 2 U 3

1 0 0

0 cos23 sin23

0 sin23 cos23

cos13 0 e iCP sin13

0 1 0

e iCP sin13 0 cos13

cos12 sin12 0

sin12 cos12 0

0 0 1

1 0 0

0 e i / 2 0

0 0 e i / 2i

?

atmospheric, K2K reactor and accelerator 0SNO, solar SK, KamLAND

12 ~ 32° 23 = ~ 45° 13 = ? ?

• What ise fraction of 3?

• Ue3 is a gateway to CP violation in neutrino sector: P( e) - P( e) sin(212)sin(223)cos2(13)sin(213)sin

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Current Knowledge of 13

Direct search

At m231 = 2.5 103 eV2,

sin22 < 0.15

allowed region

Fogli etal., hep-ph/0506083

Sin2(213) < 0.09

Sin2213 < 0.18

Best fit value of m232 = 2.4103

eV2

Global fit

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• No good reason(symmetry) for sin2213 =0

• Even if sin2213 =0 at tree level, sin2213 will not vanish at low energies with radiative corrections

• Theoretical models predict sin2213 ~ 0.001-0.1

An experiment with a precision for sin2213 better than 0.01 is desired

An improvement of an order of magnitude overprevious experiments

Typical precision: 3-6%

0.985

0.99

0.995

1

0 1 2 3 4 5 6 7 8Rat

io(1

.8 k

m/P

redi

cted

fro

m 0

.3 k

m)

Prompt Energy (MeV)

sin2 213 = 0.01

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Daya Bay: Goals And Approach

• Utilize the Daya Bay nuclear power facilities to:

- determine sin2213 with a sensitivity of 1%- measure m2

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• Adopt horizontal-access-tunnel scheme:

- mature and relatively inexpensive technology- flexible in choosing overburden and changing baseline- relatively easy and cheap to add experimental halls- easy access to underground experimental facilities - easy to move detectors between different

locations with good environmental control.

• Employ three-zone antineutrino detectors.

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How to reach 1% precision ?• Increase statistics:

– Powerful nuclear reactors(1 GWth: 6 x 1020 e/s)

– Larger target mass

• Reduce systematic uncertainties:– Reactor-related:

• Optimize baseline for best sensitivity and smaller residual 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)– Background-related

• Go deep to reduce cosmic-induced backgrounds• Enough active and passive shieldingEnough active and passive shielding

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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

55 k

m

45 km

The Daya Bay Nuclear Power Facilities

• 12th most powerful in the world (11.6 GW)• Top five most powerful by 2011 (17.4 GW)• Adjacent to mountain, easy to construct tunnels to reach underground labs with sufficient overburden to suppress cosmic rays

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Where To Place The Detectors ?

P(e e )1 sin2 213 sin2 m312 L

4E

cos413 sin2 212 sin2 m21

2 L

4E

• Place near detector(s) close to reactor(s) to measure raw flux and spectrum of e, reducing reactor-related systematic

• Position a far detector near the first oscillation maximum to get the highest sensitivity, and also be less affected by 12

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

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

neardetector

fardetector

Sin2 = 0.1m2

31 = 2.5 x 10-3 eV2

Sin2 = 0.825m2

21 = 8.2 x 10-5 eV2

10Total length: ~3100 mDaya Bay

NPP, 22.9 GW

Ling AoNPP, 22.9 GW

Ling Ao-ll NPP(under construction)

22.9 GW in 2010

295 m

81

0 m

465 m900 m

Daya Bay Near site363 m from Daya BayOverburden: 98 m

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

entrance

Filling hall

Constructiontunnel

4 x 20 tons target mass at far site

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

Water hall

Daya Bay Layout

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RPCWater Cerenkov

Veto muon system

Daya Bay Detector

Anti-neutrino Detector

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Anti-neutrino Detector modules• Three zones modular structure:

I. target: Gd-loaded scintillator

-catcher: normal scintillator

III. Buffer shielding: oil

• Reflector at top and bottom• 192 8”PMT/module• Photocathode coverage: 5.6 % 12%(with reflector)

20 t

Gd-LS

LSoil

E/E = 12%/E r = 13 cm

Target: 20 t, 1.6m-catcher: 20t, 45cmBuffer: 40t, 45cm

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Inverse-beta Signals

Antineutrino Interaction Rate(events/day per 20 ton module)Daya Bay near site 960 Ling Ao near site 760 Far site 90

Delayed Energy SignalPrompt Energy Signal

Statistics comparable to a single module at far site in 3 years.

Ee+(“prompt”) [1,8] MeVEn-cap (“delayed”) [6,10] MeVtdelayed-tprompt [0.3,200] s

1 MeV 8 MeV

6 MeV 10 MeV

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Gd-loaded Liquid Scintillator

Baseline recipe: Linear Alkyl Benzene (LAB) doped with organic Gd complex (0.1% Gd mass concentration)

LAB (suggested by SNO+): high flashpoint, safer for environment and health, commercially produced for detergents.

Stability of light attenuation two Gd-loaded LAB samples over 4 months

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Calibrating Energy Cuts

Automated deployed radioactive sources to calibrate the detector energy and position response within the entire range.

68Ge (0 KE e+ = 20.511 MeV ’s) 60Co (2.506 MeV ’s) 238Pu-13C (6.13 MeV ’s, 8 MeV n-capture)

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• Multiple anti-neutrino Multiple anti-neutrino detector modules for detector modules for side-by-side cross checkside-by-side cross check

• Multiple muon tagging detectors:– Water pool as

Cherenkov counter– Water modules along the

walls and floor as muon tracker

– RPC at the top as muon tracker

– Combined efficiency > (99.5 0.25) %

Background reduction: redundant and efficient muon veto system

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Backgrounds• Any set of events which mimics a delayed coincidence sequence is

background• The primary backgrounds are:

– The -delayed neutron emitters: 9Li and 8He– Fast neutrons– Accidentals

• All of the above can be measured

Daya Bay Ling Ao Far Site

9Li and 8He 0.3 % 0.2 % 0.2 %

Fast neutrons 0.1 % 0.1 % 0.1 %

Accidentals < 0.2 % < 0.2 % < 0.1 %

Background to Signal Events

Neutrino signal rate 930/day 760/day 90/day

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Systematic Uncertainty Budget

• Baseline is what we anticipate without further R&D• Goal is with R&D• We have made the modules portable so we can carry out swapping if necessary

Detector Related Uncertainties

Reactor Related Uncertainties• By using near detectors, we can achieve the following relative systematic uncertainties:

– With four cores operating 0.087 %– With six cores operating 0.126 %

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Summary of Systematic Uncertainties

sources Uncertainty

Neutrinos from Reactor

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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90% confidence level90% confidence level

Use rate and spectral shapeUse rate and spectral shape

Sensitivity of Daya Bay in sin2213

Daya Baynear hall

(40 t)

Tunnel entrance

Ling Aonear hall

(40 t)

Far hall(80 t)

Super-K90% CL

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Geotechnical Survey

• No active or large fault• Earthquake is infrequent• Rock structure: massive and

blocky granite• Rock mass: most is slightly

weathered or fresh• Groundwater: low flow at the

depth of the tunnel• Quality of rock mass: stable

and hard

Good geotechnical conditions for tunnel construction

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hall 4

hall 5

hall 1

hall 2

hall 3

Seepage Water sump

SAB & …

Main portal

Tunnel and Experiment Hall Layout

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Experiment Hall (#1)

Auxiliary rooms

RefugeElectricity

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Funding and supports• Funding Committed from China

• Chinese Academy of Sciences, • Ministry of Science and Technology• Natural Science Foundation of China• China Guangdong Nuclear Power Group• Shenzhen municipal government• Guangdong provincial government

Total ~20 M$

• China will provide civil construction and ~half of the detector systems; • Support by funding agencies from other countries & regions

IHEP & CGNPG

• U.S. will provide ~half of the detector cost• Funding in the U.S.

R&D funding from DOECD2 review in Jan. 2008

• Funding from other organizations and regions is proceeding

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North America (14)

BNL, Caltech, George Mason Univ., LBNL,

Iowa state Univ. Illinois Inst. Tech., Princeton,

RPI, UC-Berkeley, UCLA, Univ. of Houston,

Univ. of Wisconsin, Virginia Tech.,

Univ. of Illinois-Urbana-Champaign,

Asia (18) IHEP, Beijing Normal Univ., Chengdu Univ. of Sci. and Tech., CGNPG, CIAE, Dongguan Polytech. Univ., Nanjing Univ.,Nankai Univ.,

Shenzhen Univ., Tsinghua Univ., USTC, Zhongshan Univ., Hong Kong Univ.

Chinese Hong Kong Univ., Taiwan Univ., Chiao Tung Univ., National United Univ.

Europe (3)

JINR, Dubna, Russia

Kurchatov Institute, Russia

Charles University, Czech Republic

Daya Bay collaboration

~ 190 collaborators

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Summary• Using the high-power Daya Bay Nuclear Power Plant and

a large target mass of liquid scintillator, the Daya Bay Neutrino Experiment is poised to make the most sensitive measurement of sin2213.

• Design of detectors is in progress and R&D is ongoing.

• US CD2 Review scheduled on Jan. 2008.

• Start civil construction in Oct. 2007, Daya Bay near detector operation in 2009, and full operation in 2010