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  13  The Last Unknown Neutrino Mixing Angle U MNSP Matrix ? atmospheric, K2K reactor and accelerator 0  SNO, solar SK, KamLAND  12 ~ 32°  23 = ~ 45°  13 = ? ? What is  e fraction of 3 ? U e3 is a gateway to CP violation in neutrino sector: P(   e ) - P(     e )  sin(2  12 )sin(2  23 )cos 2 (  13 )sin(2  13 )sin 

4 Current Knowledge of  13 Direct search At  m 2 31 = 2.5  10  3 eV 2, sin 2 2   < 0.15 allowed region Fogli etal., hep-ph/ Sin 2 (2  13 ) < 0.09 Sin 2 2  13 < 0.18 Best fit value of  m 2 32 = 2.4  10  3 eV 2 Global fit

5 No good reason(symmetry) for sin 2 2  13 =0 Even if sin 2 2  13 =0 at tree level, sin 2 2  13 will not vanish at low energies with radiative corrections Theoretical models predict sin 2 2  13 ~ An experiment with a precision for sin 2 2  13 better than 0.01 is desired An improvement of an order of magnitude over previous experiments Typical precision: 3-6% sin 2 2  13 = 0.01

6 Daya Bay: Goals And Approach Utilize the Daya Bay nuclear power facilities to: - determine sin 2 2  13 with a sensitivity of 1% - measure  m 2 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 GW th : 6 x  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 Ling Ao NPP: 2  2.9 GW th Daya Bay NPP: 2  2.9 GW th 1 GW th generates 2 ×  e per sec 55 km 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 ? 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: Large-amplitude oscillation due to  12 Small-amplitude oscillation due to  13 integrated over E near detector far detector Sin 2   = 0.1  m 2 31 = 2.5 x eV 2 Sin 2   =  m 2 21 = 8.2 x eV 2

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

11 RPC Water 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 LS oil  E /E = 12%/  E  r = 13 cm Target: 20 t, 1.6m  -catcher: 20t, 45cm Buffer: 40t, 45cm

13 Inverse-beta Signals Antineutrino Interaction Rate (events/day per 20 ton module) Daya Bay near site 960 Ling Ao near site760 Far site 90 Delayed Energy Signal Prompt Energy Signal Statistics comparable to a single module at far site in 3 years. E e+ (“prompt”)  [1,8] MeV E n-cap (“delayed”)  [6,10] MeV t delayed -t prompt  [0.3,200]  s 1 MeV8 MeV 6 MeV10 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. 68 Ge (0 KE e + = 2  MeV  ’s) 60 Co (2.506 MeV  ’s) 238 Pu- 13 C (6.13 MeV  ’s, 8 MeV n-capture)

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17 Multiple anti-neutrino detector modules for side-by-side cross checkMultiple anti-neutrino detector modules for side-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: 9 Li and 8 He –Fast neutrons –Accidentals All of the above can be measured Daya BayLing AoFar Site 9 Li and 8 He0.3 %0.2 % Fast neutrons0.1 % Accidentals< 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 % –With six cores operating %

20 Summary of Systematic Uncertainties sourcesUncertainty Neutrinos from Reactor 0.087% (4 cores) 0.13% (6 cores) Detector (per module) 0.38% (baseline) 0.18% (goal) Backgrounds0.32% (Daya Bay near) 0.22% (Ling Ao near) 0.22% (far) Signal statistics0.2%

21 90% confidence level Use rate and spectral shape Sensitivity of Daya Bay in sin 2 2  13 Daya Bay near hall (40 t) Tunnel entrance Ling Ao near hall (40 t) Far hall (80 t) Super-K 90% 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 Refuge Electricity

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 DOE CD2 review in Jan 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

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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 sin 2 2  13. Design of detectors is in progress and R&D is ongoing. US CD2 Review scheduled on Jan Start civil construction in Oct. 2007, Daya Bay near detector operation in 2009, and full operation in 2010