Daya Bay Neutrino Oscillation Experiment Yee Bob Hsiung

Daya Bay Neutrino Oscillation Experiment Yee Bob Hsiung Natinal Taiwan University, Taipei, Taiwan (on behalf of the Daya Bay Collaboration) NTU-UCDavis Workshop@ NTU 12/15/2008 1

Physics Motivation weak eigenstate mass eigenstate Pontecorvo-Maki-Nakagawa-Sakata Matrix Parametrize the PMNS matrix as: Solar, reactor and accelerator Atmospheric, accelerator 23 ~ 45° 13 = ? 12 = ~ 32° 13 is the gateway of CP violation in lepton sector! 0 2

Current Knowledge of 13 Chooz: Best experimental Limit on 13 3

Measuring 13 Using Reactor Anti-neutrinos Electron anti-neutrino disappearance probability Small oscillation due to 13 < 2 km Large oscillation due to 12 > 50 km Osc. prob. (integrated over En ) vs distance e disappearance at short baseline(~2 km): unambiguous measurement of 13 Sin 22 13 = 0. 1 m 231 = 2. 5 x 10 -3 e. V 2 Sin 22 12 = 0. 825 m 221 = 8. 2 x 10 -5 e. V 2 4

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 underground to reduce cosmic-induced backgrounds • Enough active and passive shieldings 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

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 7

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 8

Civil Construction in progress Construction tunnel SAB Entrance tunnel 9

Daya Bay Detector Veto muon system RPC Water Cerenkov Anti-neutrino Detector 10

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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

Acrylic Vessel Prototype Manufacture: Naknao, Kaoshiung, Taiwan 1 m prototype for Aberdeen 3 m inner vessel for Daya. Bay 1 cm wall thickness 1. 5 cm top/bottom 13

Light Transmission Acrylic samples from Taiwan local vendor and Japan 14

Reynolds in CO. US 15

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 16

Gd-loaded Liquid Scintillator Baseline recipe: Linear Alkyl Benzene (LAB) doped with organic Gd complex (0. 1% Gd mass concentration) q. Short capture time and high released energy from capture, good for suppressing background LAB (suggested by SNO+): high flashpoint, safer for environment and health, commercially produced for detergents. Stability of light attenuation 17

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Calibrating Energy Cuts Automated deployed radioactive sources to calibrate the detector energy and position response within the entire range. (0 KE e+ = 2 0. 511 Me. V ’s) 252 Cf (~4 neutrons/fission, 2. 2 Me. V n-p and 8 Me. V n-Gd captures) LEDs (timing and PMT gains) R=0 R=1. 775 m R=1. 35 m 68 Ge In addition, cosmogenic background (n and beta emitters) provide 21 additional energy scale calibration sampled over the entire fiducial volume

Muon Veto System Surround detectors with at least 2. 5 m of water, which shields the external radioactivity and cosmogenic background Water shield is divided into two optically separated regions (with reflective divider, 8” PMTs mounted at the zone boundaries), which serves as two active and independent muon tagger Augmented with a top muon tracker: RPCs Combined efficiency of tracker > 99. 5% with error measured to better than 0. 25% 22

Muon System Active Components • Inner water shield 415 8” PMTs – PMT coverage ~1/6 m 2 on bottom and on two surfaces of side sections – • Outer water shield – 548 8” PMTs – 8” PMTs 1 per 4 m 2 along sides and bottom - 0. 8% coverage • RPCs – 756 2 m chambers in 189 modules – 6048 readout strips 23

Readout and Trigger system 24

Backgrounds Background = “prompt”+”delayed” signals that fake inverse-beta events Three main contributors, all can be measured: Background type Experimental Handle Muon-induced fast neutrons (prompt recoil, delayed capture) from water or rock >99. 5% parent “water” muons tagged ~1/3 parent “rock” muons tagged 9 Li/8 He (T 1/2= 178 msec, b decay w/neutron emission, delayed capture) Tag parent “showing” muons Accidental prompt and delay coincidences Single rates accurately measured B/S: DYB site Fast n / signal 9 Li-8 He / signal Accidental/signal LA site Far site 0. 1% 0. 3% <0. 2% 0. 1% 0. 2% <0. 1% 25

Baseline Systematics Budget Detector Related Reactor related Backgrounds Signal statistics 0. 38% 0. 13% 0. 3% (Daya Bay near), 0. 2% (Ling Ao near and far) 0. 2% (3 years of running) 26

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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 (Taiwan, Hong Kong, Russia, Czech) • U. S. will provide ~half of the detector cost • Funding in the U. S. R&D funding from DOE CD 2/3 review in 2008 • Funding from other organizations and regions is proceeding (expect Taiwan ~1 M$, Hong Kong ~2 M$, etc. ) 28

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, ~ 207 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. , National Taiwan Univ. , National Chiao Tung Univ. , National United Univ. 29

Schedule of the project • Schedule – 2003 -2007 proposal, R&D, engineering design, secure funding – 2007 -2009 Civil Construction – 2007 -2009 Detector construction – 2009 -2010 Installation and testing (one Near hall running) – 2011 Operation with full detector 30

Summary • Knowing sin 22 13 to 1% level is crucial for the future of the neutrino physics, particularly for the leptonic CP violation • Reactor experiments to measure sin 22 13 to the desired precision are feasible in the near future • Daya Bay experiment, located at an ideal site, will reach a sensitivity of <0. 01 for sin 22 13 • R&D work is going on well, detailed engineering design of detector is near finished • Tunnel construction started on Oct 10, 2007 • Deploying detectors in 2009, and begin full operation in 2010 and reach the design sensitivity by 2013 31

• Backup slides 32

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