1
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
2
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
3
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
4
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
5
• 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
6
Daya Bay: Goals And Approach
• Utilize the Daya Bay nuclear power facilities to:
- determine sin2213 with a sensitivity of 1%- measure m2
31
• 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
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
8
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
9
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
11
RPCWater Cerenkov
Veto muon system
Daya Bay Detector
Anti-neutrino Detector
12
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
13
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
14
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
15
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)
16
17
• 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
18
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
19
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 %
20
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%
21
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
22
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
23
hall 4
hall 5
hall 1
hall 2
hall 3
Seepage Water sump
SAB & …
Main portal
Tunnel and Experiment Hall Layout
24
Experiment Hall (#1)
Auxiliary rooms
RefugeElectricity
25
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
26
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
27
28
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