1. Daya Bay Reactor Neutrino Experiment
Xiaonan Li
IHEP, Beijing, China
(on behalf of the Daya Bay Collaboration)
IEEE NSS/MIC 2007

2. Physics Motivation Weak eigenstate  mass eigenstate 
Pontecorvo-Maki-Nakagawa-Sakata Matrix
Parametrize the PMNS matrix as:
Solar, reactor
reactor and accelerator
Atmospheric, accelerator
0
23 ~ 45°
12 = ~ 32°
13 = ?
13 is the gateway of CP violation in lepton sector!

3. Current Knowledge of 13 Global fit Direct search allowed region
At m231 = 2.5  103 eV2,
sin22 < 0.15
Sin2(213) < 0.09
Sin2213 < 0.18
allowed region
Best fit value of m232 = 2.4103 eV2
Fogli etal., hep-ph/

4. Small oscillation due to q13 Large oscillation due to q12
Measuring 13 Using Reactor Anti-neutrinos
Electron anti-neutrino disappearance probability
Small oscillation due to q13
< 2 km
Large oscillation due to q12
> 50 km
Osc. prob. (integrated over En ) vs distance
e disappearance at short baseline(~2 km): unambiguous measurement of 13
Sin22q13 = 0.1
Dm231 = 2.5 x 10-3 eV2
Sin22q12 = 0.825
Dm221 = 8.2 x 10-5 eV2

5. 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 shielding

6. Daya Bay: Goals And Approach
Utilize the Daya Bay nuclear power facilities to:
- determine sin2213 with a sensitivity of 1%
- measure m231
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.

7. The Daya Bay Nuclear Power Facilities
55 km
45 km
The Daya Bay Nuclear Power Facilities
Ling Ao II NPP:
2  2.9 GWth
Ready by
Ling Ao NPP:
2  2.9 GWth
1 GWth generates 2 × 1020 e per sec
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
Daya Bay NPP:
2  2.9 GWth

8. Daya Bay Layout 4 x 20 tons target mass at far site
1615 m from Ling Ao
1985 m from Daya
Overburden: 350 m
Ling Ao Near site
~500 m from Ling Ao
Overburden: 112 m
900 m
Ling Ao-ll NPP
(under construction)
22.9 GW in 2010
465 m
Water hall
Construction
tunnel
810 m
Ling Ao
NPP, 22.9 GW
Filling hall
entrance
Daya Bay Near site
363 m from Daya Bay
Overburden: 98 m
295 m
Daya Bay
NPP, 22.9 GW
Total length: ~3100 m

9. Daya Bay Detector Veto muon system Anti-neutrino Detector RPC
Water Cerenkov
Anti-neutrino Detector

10. Detection of e Inverse -decay in Gd-doped liquid scintillator:
 + p  D + (2.2 MeV) (t~180μs)
0.3b
+ Gd  Gd* Gd + ’s(8 MeV) (t~30μs)
50,000b
Time, space and energy-tagged signal
 suppress background events.
E  Te+ + Tn + (mn - mp) + m e+  Te MeV

11. Anti-neutrino Detector modules
Three zones modular structure:
I. target: Gd-loaded scintillator
II. g-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 LS
oil
sE/E = 12%/E
sr = 13 cm
Target: 20 t, 1.6m
g-catcher: 20t, 45cm
Buffer: 40t, 45cm

12. Inverse-beta Signals Ee+(“prompt”) [1,8] MeV
Antineutrino Interaction Rate
(events/day per 20 ton module)
Daya Bay near site 960
Ling Ao near site 760
Far site
Ee+(“prompt”) [1,8] MeV
En-cap (“delayed”)  [6,10] MeV
tdelayed-tprompt  [0.3,200] s
Delayed Energy Signal
Prompt Energy Signal
Statistics comparable to a single module at far site in 3 years.
1 MeV
8 MeV
6 MeV
10 MeV

13. Gd-loaded Liquid Scintillator
Baseline recipe: Linear Alkyl Benzene (LAB) doped with organic Gd complex (0.1% Gd mass concentration)
Short capture time and high released energy from capture, good for suppressing background
LAB (suggested by SNO+): high flashpoint, safer for environment and health, commercially produced for detergents.
Stability of light attenuation

14. Calibrating Energy Cuts
Automated deployed radioactive sources to calibrate the detector energy and position response within the entire range.
68Ge (0 KE e+ = 20.511 MeV ’s)
252Cf (~4 neutrons/fission, 2.2 MeV n-p and 8 MeV n-Gd captures)
LEDs (timing and PMT gains)
R=1.35m
R=0
R=1.775 m
In addition, cosmogenic background (n and beta emitters) provide additional energy scale calibration sampled over the entire fiducial volume

15. Muon Veto System
Surround detectors with at least 2.5m of water, which shields the external radioactivity and cosmogenic background
Water shield is divided into two optically separated regions (with reflective divider, 8” PMTs mounted at the zone boundaries), which serves as two active and independent muon tagger
Augmented with a top muon tracker: RPCs
Combined efficiency of tracker > 99.5% with error measured to better than 0.25%

16. Muon System Active Components
Inner water shield
415 8” PMTs
PMT coverage ~1/6m2 on bottom and on two surfaces of side sections
Outer water shield
548 8” PMTs
8” PMTs 1 per 4m2 along sides and bottom - 0.8% coverage
RPCs
756 2m  2m chambers in 189 modules
6048 readout strips

17. Readout and Trigger system

18. DYB site LA site Far site
Backgrounds
Background = “prompt”+”delayed” signals that fake inverse-beta events
Three main contributors, all can be measured:
Background type
Experimental Handle
Muon-induced fast neutrons (prompt recoil, delayed capture) from water or rock
>99.5% parent “water” muons tagged
~1/3 parent “rock” muons tagged
9Li/8He (T1/2= 178 msec, b decay w/neutron emission, delayed capture)
Tag parent “showing” muons
Accidental prompt and delay coincidences
Single rates accurately measured
B/S:
DYB site
LA site
Far site
Fast n / signal
0.1%
9Li-8He / signal
0.3%
0.2%
Accidental/signal
<0.2%
<0.1%

19. Baseline Systematics Budget
Detector Related
0.38%
Reactor related
0.13%
Backgrounds
0.3% (Daya Bay near),
0.2% (Ling Ao near and far)
Signal statistics
0.2% (3 years of running)

21. 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 DOE
CD2 review in Jan. 2008
Funding from other organizations and regions is proceeding

22. Daya Bay collaboration
Europe (3)
JINR, Dubna, Russia
Kurchatov Institute, Russia
Charles University, Czech Republic
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.
~ 190 collaborators

23. Schedule of the project
proposal, R&D,
engineering design,
secure funding
Civil Construction
Detector construction
Installation and testing
(one Near hall running)
Operation with full detector

24. Summary
Knowing Sin22q13 to 1% level is crucial for the future of the neutrino physics, particularly for the leptonic CP violation
Reactor experiments to measure Sin22q13 to the desired precision are feasible in the near future
The Daya Bay experiment, located at an ideal site, will reach a sensitivity of <0.01 for sin2213
R&D work is going on well, detailed engineering design of detector is near finished
tunnels construction started on Oct 10, 2007
Deploying detectors in 2009, and begin full operation in 2010