1. Daya Bay and Other Reactor Neutrino Oscillation Experiments
Jen-Chieh Peng
University of Illinois at Urbana-Champaign
International Workshop on “High Energy Physics in the LHC Era” Valparaiso, Chile, December 11-15, 2006

2. Outline

3. What we have learned from neutrino oscillation experiments

4. 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 …..

5. What we know and do not know about the neutrinos
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)

6. Why measuring θ13?
A recent tabulation of predictions of 63 neutrino mass models on sin2θ13
(hep-ph/ )
Models based on the Grand Unified Theories in general give relatively large θ13
Models based on leptonic symmetries predict small θ13
A measurement of sin22θ13 at the sensitivity level of 0.01 can rule out at least half of the models!

7. Why measuring θ13?
A recent tabulation of predictions of 63 neutrino mass models on sin2θ13
(hep-ph/ )
A measurement of sin22θ13 AND the mass hierarchy can rule out even more models!

8. Why measuring θ13? Leptonic CP violation
If sin22θ13> , then NOvA+T2K will have good coverage on CP δ.
Reactor experiments sets the scale for future studies

9. Current Knowledge of 13 Global fit Direct search allowed region
sin2213 < 0.11 (90% CL)
Best fit value of m232 = 2.4  103 eV2
sin2213 = 0.04
At m231 = 2.5  103 eV2,
sin22 < 0.17
allowed region
Fogli etal., hep-ph/

10. Some Methods For Determining 13
Method 1: Accelerator Experiments
decay pipe
horn
absorber
target p
detector + +
  e appearance experiment
need other mixing parameters to extract 13
baseline O( km), matter effects present
expensive
Method 2: Reactor Experiments
e  X disappearance experiment
baseline O(1 km), no matter effect, no ambiguity
• relatively cheap

11. Discovery of the Neutrino – 1956
F. Reines, Nobel Lecture, 1995

12. Detecting : Inverse  Decay
The reaction is the inverse -decay in 0.1% Gd-doped liquid scintillator:
e  p  e+ + n (prompt)
 + p  D + (2.2 MeV) (delayed)
+ Gd  Gd*
 Gd + ’s(8 MeV) (delayed)
0.3b
50,000b
Arbitrary
Flux
Cross Section
Observable n Spectrum
From Bemporad, Gratta and Vogel
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 MeV
10-40 keV

13. Measuring 13 with Reactor Neutrinos
Search for 13 in new oscillation experiment
Small-amplitude oscillation due to 13 integrated over E
Large-amplitude
oscillation due to 12
13
m213≈ m223
Reactor theta13 is an LDRD activity here at Berkeley, Daya Bay has emerged as one of leading contenders in worldwide effort to mount next-generation reactor neutrino experiment.
~1-1.8 km
detector 1
detector 2
> 0.1 km

14. Results from Chooz Systematic uncertainties P = 8.4 GWth L = 1.05 km
5-ton 0.1% Gd-loaded liquid scintillator
to detect e + p  e+ + n
L = 1.05 km
D = 300 mwe
P = 8.4 GWth
~3000 e candidates
(included 10% bkg) in
335 days
Systematic uncertainties
Rate:
~5 evts/day/ton (full power)
including bkg/day/ton

15. How to Reach a Precision of 0.01 in sin2213?
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)

16. World of Proposed Reactor Neutrino Experiments
Chooz, France
Krasnoyasrk, Russia
Braidwood, USA
Kashiwazaki, Japan
RENO, Korea
Diablo Canyon, USA
Daya Bay, China
Angra, Brazil

17. Reactor 13 Experiment at Krasnoyarsk, Russia
Original ideal, first proposed at Neutrino2000
Krasnoyarsk
- underground reactor
- detector locations determined by infrastructure
~20000 ev/year
~1.5 x 106 ev/year
Reactor
Ref: Marteyamov et al,
hep-ex/

18. KASKA at Kashiwazaki, Japan
Kashiwazaki-Kariwa
Nuclear Power Station
- 7 nuclear power stations, World’s most powerful reactors
- requires construction of underground shaft for detectors
near
far
70 m m
6 m shaft hole, m depth
sin2(213) < 0.02
See poster by F. Suekane

20. Daya Bay collaboration
Europe (3) (9)
JINR, Dubna, Russia
Kurchatov Institute, Russia
Charles University, Czech Republic
North America (13)(46)
BNL, Caltech, 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 (13) (70)
IHEP, CIAE,Tsinghua Univ.
Zhongshan Univ.,Nankai Univ.
Beijing Normal Univ., Nanjing Univ.
Shenzhen Univ., Hong Kong Univ.
Chinese Hong Kong Univ.
Taiwan Univ., Chiao Tung Univ.,
National United Univ.
~ 125 collaborators

21. Location of Daya Bay
45 km from
Shenzhen
55 km from
Hong Kong

22. 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
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
Daya Bay NPP:
2  2.9 GWth

23. Total length: ~3100 m Far site 1615 m from Ling Ao
1985 m from Daya
Overburden: 350 m
Empty detectors: moved to underground halls through access tunnel.
Filled detectors: transported between underground halls via horizontal tunnels.
900 m
Ling Ao Near
~500 m from Ling Ao
Overburden: 112 m
Mid site
873 m from Ling Ao
1156 m from Daya
Overburden: 208 m
Ling Ao-ll NPP
(under const.)
465 m
810 m
Construction
tunnel
Ling Ao
NPP
Filling hall
entrance
295 m
Daya Bay Near
363 m from Daya Bay
Overburden: 98 m
Daya Bay
NPP
Total length: ~3100 m

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

25. 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 ~ months
A similar tunnel on site as a reference

26. 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
20 ton
0.1% Gd-LS
 catcher
buffer

27. Event Rates per Detector Module
Source
Units DB LA
far
Use
Antineutrino Signal
(day-1)
930
760 90
signal
Radioactive Backgrounds
(Hz) 30
e+-thresh.
Rock 4
PMT glass 8
other materials (steel) 18
Gd contamination 1
Muons 24 14
Single neutron
9000
6000
400
cal.
Tagged single neutron
480
320 45
cal./bkg.
Tagged fast neutron 20 13 2
Bkg est
b emitters (6-10 MeV)
210
140 15
n-thresh.
12B
270 28
8He+9Li 3
Bkg

28. Key Requirements for Gd-LS for Daya Bay
High light transmission = high optical attenuation length (low optical absorbance).
High light output in the Liquid Scintillator, LS.
Long-term chemical stability, since the experiment will go on for at least 3 years.
Stability of the LS means no development of color; no colloids, particulates, cloudiness, nor precipitation; no gel formation; no changes in optical properties.

29. 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).

30. Detector Prototype at IHEP
0.5 ton prototype
(currently unloaded liquid scintillator)
45 8” EMI PMTs:
14% effective photocathode coverage with top/bottom reflectors
~240 photoelectron
per MeV :
9%/E(MeV)
prototype detector at IHEP
Put in difference plot
Energy Resolution

31. Background Sources
1. 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

32. Cosmic-ray Muon
Use a modified Geiser parametrization for cosmic-ray flux at surface
Apply MUSIC and mountain profile to estimate muon intensity & energy
355 m
98 m
112 m
208 m
Daya Bay
Ling Ao
Far
Mid
DYB
LingAo
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

33. (Water buffer + water cherenkov + RPC tracker)
Muon Veto System
(Water buffer + water cherenkov + RPC tracker)
Water shield also serves as a
Cherenkov counter for tagging
muons
Water Cherenkov modules
along the walls and floor
Augmented with a muon
tracker: RPCs
Combined efficiency of Cherenkov
and tracker > 99.5% with error
measured to better than 0.25%

34. 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%

35. Funding and other supports
Funding Committed from
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
Gained strong support from:
China atomic energy agency
China nuclear safety agency
Supported by BNL/LBNL seed funds
Supported by DOE $800K R&D fund
Support by funding agencies from other
countries & regions
China plans to provide civil construction and ~half of the detector
systems; U.S.plans to bear ~half of the detector cost
IHEP & CGNPG
IHEP & LBNL

36. Schedule begin civil construction April 2007
Bring up the first pair of detectors Jun 2009
Begin data taking with the Near-Mid
configuration Sept 2009
Begin data taking with the Near-Far
configuration Jun 2010

37. Sensitivity to Sin22q13 Other physics capabilities:
Supernova watch, Sterile neutrinos, …

38. Double Chooz 0.1-0.2 km 1.05 km Sensitivity 10 tons detectors
8.4 GWth reactor power
300 mwe overburden at far site
60 mwe overburden at near site km
1.05 km
Sensitivity
sin2(213) < 0.03 at 90% CL
after 3 yrs, matm2 = 2 x 10-3 eV2

40. Reactor Experiment for Neutrino Oscillations (RENO) at YongGwang, Korea
20tons (fid. vol.) of liquid scintillator detectors
3 nearest detectors of 200~300kg scintillators
Begin of data taking 2009/2010
sin2(213) < 0.02
(88m high)
(260m high)
Near Detector
Tunnel length: ~100m
Far Detector
Tunnel length: ~600m
150m
~1.5 km

42. Prospects for a Reactor Measurement of sin2213
Angra, Brazil sin2213 < 0.005
R&D on reactor monitoring. Proposal for 13 measurement after Double Chooz.
Daya Bay, China sin2213 < 0.01
Approved by the Chinese Academy of Science for 50M RMB.
Other Chinese agencies are expected to contribute ~100M RMB.
US DOE has provided 0.8M$ for R&D for FY06. Working towards US project start in FY08.
Plan to start near-mid data taking in 2009, and begin full operation in 2010.
Double-CHOOZ, France sin2213 < 0.03
Funding committment in France and Germany.
Begin running far detector in 2008.
Complete near detector in 2009.
RENO, Korea sin2213 < 0.02
Approved by Ministry of Science and Technology for US $9M. R&D program starting.
Plan to begin data taking in 2009/2010.

43. Neutrino Physics at Reactors
Past Experiments
Hanford
Savannah River
ILL, France
Bugey, France
Rovno, Russia
Goesgen, Switzerland
Krasnoyark, Russia
Palo Verde
Chooz, France
Reactors in Japan
1956
First observation of neutrinos
1980s & 1990s
Reactor neutrino flux measurements in U.S. and Europe
1995
Nobel Prize to Fred Reines at UC Irvine
2002
Discovery of reactor antineutrino oscillation
2006 and beyond Precision measurement of 13
Exploring feasibility of CP violation studies

44. S. Glashow