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1
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)
2
Outline
13 Physics case for a precise measurement
The proposed Daya Bay neutrino oscillation
experiment
Schedule and expected sensitivity of the
Daya Bay experiment
3
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
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
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)
6
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)
7
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)
8
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
9
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
10
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
11
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
12
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
23
detector 1 detector 2
13
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
14
• 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?
15
World of Proposed Reactor Neutrino Experiments
Angra, Brazil
Diablo Canyon, USA
Braidwood, USAChooz, France Krasnoyasrk, Russia
Kashiwazaki, Japan
RENO, Korea
Daya Bay, China
17
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
18
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
21
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
22
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
24
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).
26
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
27
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
28
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
30
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
31
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
32
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%