Daya Bay Reactor Neutrino Experiment Xiaonan Li IHEP, Beijing, China (on behalf of the Daya Bay Collaboration) IEEE NSS/MIC 2007
Physics Motivation Weak eigenstate mass eigenstate Pontecorvo-Maki-Nakagawa-Sakata Matrix Parametrize the PMNS matrix as: Solar, reactor Atmospheric, accelerator 0 reactor and accelerator 23 ~ 45° 13 = ? 12 = ~ 32° 13 is the gateway of CP violation in lepton sector!
Current Knowledge of 13 At m231 = 2.5 103 eV2, sin22 < 0.15 Global fit Direct search Sin2(213) < 0.09 Sin2213 < 0.18 allowed region Best fit value of m232 = 2.4103 eV2 Fogli etal., hep-ph/0506083
Measuring 13 Using Reactor Anti-neutrinos e disappearance at short baseline(~2 km): unambiguous measurement of 13 Electron anti-neutrino disappearance probability Small oscillation due to q13 < 2 km Large oscillation due to q12 > 50 km Osc. prob. (integrated over En ) vs distance Sin22q13 = 0.1 Dm231 = 2.5 x 10-3 eV2 Sin22q12 = 0.825 Dm221 = 8.2 x 10-5 eV2
How to reach 1% precision ? • Increase statistics: • Powerful nuclear reactors(1 GWth: 6 x 1020e/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
Daya Bay: Goals And Approach • Utilize the Daya Bay nuclear power facilities to: • - determine sin2213 with a sensitivity of 1% • - measure m231 • 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.
45 km 55 km The Daya Bay Nuclear Power Facilities Ling Ao II NPP: 2 2.9 GWth Ready by 2010-2011 Ling Ao NPP: 22.9 GWth 1 GWth generates 2 × 1020eper sec • 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 Daya Bay NPP: 22.9 GWth
Far site 1615 m from Ling Ao 1985 m from Daya Overburden: 350 m Daya Bay Near site 363 m from Daya Bay Overburden: 98 m 4 x 20 tons target mass at far site Daya Bay Layout Ling Ao Near site ~500 m from Ling Ao Overburden: 112 m 900 m Ling Ao-ll NPP (under construction) 22.9 GW in 2010 465 m Water hall Construction tunnel 810 m Ling Ao NPP, 22.9 GW Filling hall entrance 295 m Daya Bay NPP, 22.9 GW Total length: ~3100 m
Daya Bay Detector Veto muon system RPC Water Cerenkov Anti-neutrino Detector
Detection of e Inverse -decay in Gd-doped liquid scintillator: + p D + (2.2 MeV) (t~180μs) 0.3b • + Gd Gd* Gd + ’s(8 MeV) (t~30μs) 50,000b Time, space and energy-tagged signal suppress background events. E Te+ + Tn + (mn - mp) + m e+ Te+ + 1.8 MeV
Anti-neutrino Detector modules • Three zones modular structure: I. target: Gd-loaded scintillator II. g-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 sE/E = 12%/E sr = 13 cm Target: 20 t, 1.6m g-catcher: 20t, 45cm Buffer: 40t, 45cm
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 Ee+(“prompt”) [1,8] MeV En-cap (“delayed”) [6,10] MeV tdelayed-tprompt [0.3,200] s Prompt Energy Signal Delayed Energy Signal 1 MeV 8 MeV 6 MeV 10 MeV Statistics comparable to a single module at far site in 3 years.
Gd-loaded Liquid Scintillator • Baseline recipe: Linear Alkyl Benzene (LAB) doped with organic Gd complex (0.1% Gd mass concentration) • 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
Calibrating Energy Cuts R=1.775 m R=0 R=1.35m • Automated deployed radioactive sources to calibrate the detector energy and position response within the entire range. • 68Ge (0 KE e+ = 20.511 MeV ’s) • 252Cf (~4 neutrons/fission, 2.2 MeV n-p and 8 MeV n-Gd captures) • LEDs (timing and PMT gains) In addition, cosmogenic background (n and beta emitters) provide additional energy scale calibration sampled over the entire fiducial volume
Muon Veto System • Surround detectors with at least 2.5m 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%
Muon System Active Components • Inner water shield • 415 8” PMTs • PMT coverage ~1/6m2 on bottom and on two surfaces of side sections • Outer water shield • 548 8” PMTs • 8” PMTs 1 per 4m2 along sides and bottom - 0.8% coverage • RPCs • 756 2m 2m chambers in 189 modules • 6048 readout strips
Backgrounds Background = “prompt”+”delayed” signals that fake inverse-beta events Three main contributors, all can be measured: B/S:
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. 2008 • Funding from other organizations and regions is proceeding
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, 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. ~ 190 collaborators
Schedule of the project • Schedule • 2003-2007 proposal, R&D, engineering design, secure funding • 2007-2008 Civil Construction • 2008-2009 Detector construction • 2009-2010 Installation and testing (one Near hall running) • 2010 Operation with full detector
Summary • Knowing Sin22q13 to 1% level is crucial for the future of the neutrino physics, particularly for the leptonic CP violation • Reactor experiments to measure Sin22q13 to the desired precision are feasible in the near future • The Daya Bay experiment, located at an ideal site, will reach a sensitivity of <0.01 for sin2213 • R&D work is going on well, detailed engineering design of detector is near finished • tunnels construction started on Oct 10, 2007 • Deploying detectors in 2009, and begin full operation in 2010