Daya Bay Reactor Neutrino Experiment Changgen Yang Institute

Daya Bay Reactor Neutrino Experiment Changgen Yang Institute of High Energy Physics, Beijing for the Daya Bay Collaboration 2 nd Sino-French Workshop on the Dark Universe The 4 th International Conference on Flavor Physics, Sept 24 -28, 2007, Beijing 1

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 2

13 The Last Unknown Neutrino Mixing Angle UMNSP Matrix ? atmospheric, K 2 K reactor and accelerator 23 = ~ 45° 13 = ? SNO, solar SK, Kam. LAND 12 ~ 32° 0 ? • What is e fraction of 3? • Ue 3 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 3

Current Knowledge of 13 Direct search Global fit Sin 2(2 13) < 0. 09 At m 231 = 2. 5 10 3 e. V 2, sin 22 < 0. 15 Sin 22 13 < 0. 18 allowed region Best fit value of m 232 = 2. 4 10 3 e. V 2 Fogli etal. , hep-ph/0506083 4

• No good reason(symmetry) for sin 22 13 =0 • Even if sin 22 13 =0 at tree level, sin 22 13 will not vanish at low energies with radiative sin 2 2 13 = 0. 01 corrections • Theoretical models predict sin 22 13 ~ 0. 001 -0. 1 Typical precision: 3 -6% An experiment with a precision for sin 22 13 better than 0. 01 is desired An improvement of an order of magnitude over previous experiments 5

Daya Bay: Goals And Approach • Utilize the Daya Bay nuclear power facilities to: - determine sin 22 13 with a sensitivity of 1% - measure m 231 • 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. 6

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 7

The Daya Bay Nuclear Power Facilities 45 km 55 km Ling Ao II NPP: 2 2. 9 GWth Ready by 2010 -2011 Ling Ao NPP: 2 2. 9 GWth 1 GWth generates 2 × 1020 e per sec • 12 th 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

Where To Place The Detectors ? • Since reactor e are low-energy, it is a disappearance experiment: Small-amplitude oscillation due to 13 integrated over E • 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 Large-amplitude oscillation due to 12 Sin 22 = 0. 1 m 231 = 2. 5 x 10 -3 e. V 2 Sin 22 2 = 0. 825 m 221 = 8. 2 x 10 -5 e. V 2 far detector near detector 9

4 x 20 tons target mass at far site Ling Ao Near site ~500 m from Ling Ao Overburden: 112 m 900 Far site 1615 m from Ling Ao 1985 m from Daya Overburden: 350 m m Daya Bay Layout 465 810 m Water hall m Construction tunnel Filling hall Ling Ao-ll NPP (under construction) 2 2. 9 GW in 2010 Ling Ao NPP, 2 2. 9 GW entrance 295 m Daya Bay NPP, 2 2. 9 GW Daya Bay Near site 363 m from Daya Bay Overburden: 98 m Total length: ~3100 m 10

Daya Bay Detector Veto muon system RPC Water Cerenkov Anti-neutrino Detector 11

Anti-neutrino Detector modules • Three zones modular structure: I. target: Gd-loaded scintillator II. g-catcher: normal scintillator III. Buffer shielding: oil 20 t Gd-LS • Reflector at top and bottom • 192 8”PMT/module • Photocathode coverage: 5. 6 % 12%(with reflector) LS s. E/E = 12%/ E sr = 13 cm oil Target: 20 t, 1. 6 m g-catcher: 20 t, 45 cm Buffer: 40 t, 45 cm 12

Inverse-beta Signals Antineutrino Interaction Rate (events/day per 20 ton module) Daya Bay near site Ling Ao near site Far site Prompt Energy Signal 1 Me. V 960 760 90 Ee+(“prompt”) [1, 8] Me. V En-cap (“delayed”) [6, 10] Me. V tdelayed-tprompt [0. 3, 200] s Delayed Energy Signal 8 Me. V 6 Me. V Statistics comparable to a single module at far site in 3 years. 10 Me. V 13

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 14

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 0. 511 Me. V ’s) 60 Co (2. 506 Me. V ’s) 238 Pu-13 C (6. 13 Me. V ’s, 8 Me. V n-capture) 15

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Background reduction: redundant and efficient muon veto system • Multiple 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) % 17

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 Background to Signal Events Daya Bay Ling Ao Far Site and 8 He 0. 3 % 0. 2 % Fast neutrons 0. 1 % Accidentals < 0. 2 % < 0. 1 % 760/day 9 Li Neutrino signal rate 930/day 18

Systematic Uncertainty Budget Detector Related Uncertainties • • • 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 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 % 19

Summary of Systematic Uncertainties sources Uncertainty Neutrinos from Reactor Detector (per module) Backgrounds 0. 087% (4 cores) 0. 13% (6 cores) 0. 38% (baseline) 0. 18% (goal) 0. 32% (Daya Bay near) 0. 22% (Ling Ao near) 0. 22% (far) Signal statistics 0. 2% 20

Sensitivity of Daya Bay in sin 22 13 90% confidence level Far hall (80 t) Ling Ao near hall (40 t) Super-K 90% CL Use rate and spectral shape Tunnel entrance Daya Bay near hall (40 t) 21

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 22

Tunnel and Experiment Hall Layout hall 3 hall 2 hall 4 Main portal SAB & … hall 5 Seepage Water sump hall 1 23

Experiment Hall (#1) Auxiliary rooms Refuge Electricity 24

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$ IHEP & CGNPG • China will provide civil construction and ~half of the detector systems; • Support by funding agencies from other countries & regions • U. S. will provide ~half of the detector cost • Funding in the U. S. R&D funding from DOE CD 2 review in Jan. 2008 • Funding from other organizations and regions is proceeding 25

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, ~ 190 collaborators 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. 26

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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 22 13. • Design of detectors is in progress and R&D is ongoing. • US CD 2 Review scheduled on Jan. 2008. • Start civil construction in Oct. 2007, Daya Bay near detector operation in 2009, and full operation in 2010 28