Changgen Yang Institute of High Energy Physics, Beijing for the Daya Bay Collaboration

1. Daya Bay Neutrino Experiment Changgen Yang Institute of High Energy Physics, Beijing for the Daya Bay Collaboration International UHE Tau Neutrino Workshop, April 24-26, 2006

2. ? ? reactor and accelerator atmospheric, K2K SNO, solar SK, KamLAND 0 13 = ? 23 = ~ 45° 12 ~ 32° 13The Last Unknown Neutrino Mixing Angle UMNSP Matrix • What isefraction of3? • Ue3 is a gateway to CP violationin neutrino sector: P(  e) - P(  e)  sin(212)sin(223)cos2(13)sin(213)sin Large and maximal mixing!

4. mass hierarchy CP violation matter 13 from Reactor and Accelerator Experiments reactor - Clean measurement of 13 - No matter effects accelerator - sin2213 is missing key parameter for any measurement of CP

5. Current Knowledge of 13 At m231 = 2.5  103 eV2, sin22 < 0.15 Global fit Direct search Sin2(213) < 0.09 Sin2213 < 0.18 allowed region Best fit value of m232 = 2.4103 eV2 Fogli etal., hep-ph/0506083

6. Limitations of Past and CurrentReactor Neutrino Experiments Palo Verde, CHOOZ • Typical precision is 3-6% • due to • limited statistics • reactor-related systematic • errors: • - energy spectrum of e • (~2%) • - time variation of fuel • composition (~1%) • detector-related systematic • error (1-2%) • background-related error • (1-2%)

7. Daya Bay: Goals And Approach • Utilize the Daya Bay nuclear power facilities to: • - determine sin2213 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.

8. How To Reach A Precision of 0.01 ? • Powerful nuclear plant • Larger detectors • “Identical” detectors • Near and far detectors to minimize reactor-related errors • Optimize baseline for best sensitivity and smaller residual reactor-related errors • Interchange near and far detectors – cancel many detector systematic errors • Sufficient overburden/shielding to reduce background • Comprehensive calibration/monitoring of detectors

9. 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: 22.9 GWth 1 GWth generates 2 × 1020eper 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: 22.9 GWth

10. Small-amplitude oscillation due to 13 Large-amplitude oscillation due to 12 Where To Place The Detectors ? • Since reactor eare low-energy, it is a disappearance experiment: • 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 far detector near detector

11. Baseline optimization and site selection • Neutrino spectrum and their error • Neutrino statistical error • Reactor residual error • Estimated detector systematical error: total, bin-to-bin • Cosmic-rays induced background (rate and shape) taking into mountain shape: fast neutrons, 9Li, … • Backgrounds from rocks and PMT glass

12. Far site 1600 m from Ling Ao 2000 m from Daya Overburden: 350 m 910 m Mid site ~1000 m from Daya Overburden: 208 m 570 m 230 m (15% slope) 730 m 290 m (8% slope) Daya Bay Near 360 m from Daya Bay Overburden: 97 m Empty detectors: moved to underground halls through access tunnel. Filled detectors: swapped between underground halls via horizontal tunnels. Ling Ao Near 500 m from Ling Ao Overburden: 98 m Ling Ao-ll NPP (under const.) Ling Ao NPP Entrance portal Daya Bay NPP Total length: ~2700 m

13. A Versatile Site • Full operation: • (A) Two near sites + Far site • (B) Mid site + Far site • (C) Two near sites + Mid site + Far site • Internal checks, each with different • systematic • Rapid deployment: • - Daya Bay near site + mid site • - 0.7% reactor systematic • error

14. Geophysical profile (Daya–mid--far)

15. Zk4 (depth: 133 m) Bore Samples Zk2 (depth: ~180 m) At tunnel depth Zk1 (depth: 210 m) Zk3 (depth: ~64 m)

16. Findings of 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

17. e  p  e+ + n(prompt)  + p  D + (2.2 MeV) (delayed) • + Gd  Gd*  Gd + ’s(8 MeV) (delayed) From Bemporad, Gratta and Vogel Arbitrary Observable n Spectrum Cross Section Flux Detecting Low-energy e • The reaction is the inverse -decay in 0.1% Gd-doped liquid scintillator: 0.3b 50,000b • Time- and energy-tagged signal is a good • tool to suppress background events. • Energy of eis given by: E Te+ + Tn + (mn - mp) + m e+  Te+ + 1.8 MeV 10-40 keV

18. (3 year run) DYB: B/S = 0.5% LA: B/S = 0.4% Far: B/S = 0.1% m231 = 2  10-3 eV2 tonnes What Target Mass Should Be? Systematic error Black : 0.6% Red : 0.25% (baseline goal) Blue : 0.12%

19. 20 tonnes Gd-LS gamma catcher buffer Design of Antineutrino Detectors • Three-zonestructure: I. Target: 0.1%Gd-loaded liquid scintillator II. Gamma catcher: liquid scintillator, 45cm III. Buffer shielding: mineral oil, ~45cm • Possibly with diffuse reflection at ends. ~200 PMT’s around the barrel: Oil buffer thickness

20. 3-ZONE 2-ZONE Why three zones ? Chooz • 3 zones provides increased confidence in systematic • error associated with detection efficiency and fiducial • volume • 2 zones implies simpler design/construction, some cost • reduction but with increased risk to systematic error background n capture on Gd yields 8 MeV with 3-4g’s

21. Absorbance at 430 nm 507 days (1.2% Gd in PC) 455 days (0.2% Gd in PC) 367 days (0.2% Gd in 20% PC + 80% C12H26) 130 days(0.2% Gd in LAB) Calendar Date Gd-loaded Liquid Scintillator For Daya Bay • Require stable Gd-loaded liquid scintillator with • - high light yield • - long attenuation length • BNL/IHEP/JINR nuclear chemists study on metal-loaded liquid scintillator (~1% Gd diluted to ~0.1% Gd) for Daya Bay: • technology of 1% Gd in • pseudocumene (PC) is mature • need R&D for 1% Gd in mixture of • PC and dodecane, and with • linear alkyl benzene (LAB) BNL samples Attenuation lengths > 15 m

22. Neutron background vs thickness of water 0.30 0.25 2 m of water Fast neutrons per day 0.20 0.15 0.10 0.05 1. 2. 0. water thickness (m) Design of Shield-Muon Veto • Detector modules enclosed by 2m of water to shield neutrons and gamma-rays from surrounding rock • Water shield also serves as a Cherenkov veto • Augmented with a muon tracker: scintillator or RPCs • Combined efficiency of Cherenkov and tracker > 99.5% tunnel

23. PMT's for water Cherenkov Active Water Shield and Muon Tracker • Specifications • High efficiency muon tracker; less than 0.3% inefficiency when combined with the muon water Cherenkov • Good (ns) timing resolution to reduce accidentals due to ambient radioactivity background • Muon tracker can be deployed in water pool • Robust, good long-term stability

24. Moving Detectorsin Horizontal Tunnels Aircraft Pushback Tractors are Ideal • Zero emission vehicles available • Low-speed towing • Forward and reverse towing • Vehicle ballasted • OK for incline (<8%)

25. Prototype setup at IHEP Flange to put Source • Purposes: Test reflection, energy resolution, LS performance … • Inner acrylic vessel: 1m in diameter and 1m tall, filled with normal liquid scintillator(70% mineral oil + 30% mesitylene). • Outer stainless steel vessel: 2m in diameter and 2m tall, filled with mineral oil. PMTs mounted and immerged in oil. • 45 MACRO PMT, 15 PMT/Ring Cables LED

27. Liquid Scint. Or An Crystal Source Cs137 or Sr90 PMT Glass Tube PMT XP2020 Attenuation Length and Light Yield Lattn = 8.5+/-0.3m 61% relative to Anthracene

28. Very PreliminaryResolution: 15.5%@0.662MeV

29. Backgrounds

30. ~350 m ~98 m ~210 m ~97 m Cosmic-ray Muon • Apply modified Gaisser parametrization for cosmic-ray flux at surface • Use MUSIC and mountain profile to estimate muon flux & energy

31. Summary of Background • Use a modified Palo Verde-Geant3-based MC to model response of detector: (neutrino signal rate 560/day 80/day) Further rejection of background may be possible by cutting showering muons.

32. w/Swapping → 0 → 0.006 → 0 → 0.06% Swapping: canreduce relative uncertainty further Detector-related Uncertainties Absolute measurement Relative measurement Baseline: currently achievablerelativeuncertainty without R&D Goal: expectedrelativeuncertainty after R&D

33. Summary of Systematic Errors • Reactor-related systematic errors are: • 0.09% (4 cores) • 0.13% (6 cores) • Relative detector systematic errors are: • 0.36% (baseline) • 0.12% (goal) • 0.06% (with swapping) • These are input to sensitivity calculations

34. Far hall (80 t) 90% confidence level Near-mid Ling Ao near hall (40 t) 2 near + far (3 years) near (40t) + mid (40 t) 1 year Daya Bay near hall (40 t) Tunnel entrance Use rate and spectral shape Sensitivity of Daya Bay in sin2213

35. Synergy Between Reactor and Accelerator Experiments Before 2011: Daya Bay provides basis for early decision on future program beyond NOA for CP and mass hierarchy After 2011: Daya Bay will complement NOA and T2K for resolving q23, mass hierarchy, and CP phase

36. Overall Project Schedule

37. Summary • The Daya Bay nuclear power facility in China and the mountainous topology in the vicinity offer an excellent opportunity for carrying out a reactor neutrino program using horizontal tunnels. • The Daya Bay experiment has excellent potential to reach a sensitivity of 0.01 for sin2213. • The Daya Bay Collaboration continues to grow. • Will complete detailed design of detectors, tunnels and underground facilities in 2006. • Plan to commission the Fast Deployment scheme in 2009, and Full Operation in 2010.

38. The Daya Bay Collaboration: China-Russia-U.S. 20 institutions, 89 collaborators Yu. Gornushkin, R. Leitner, I. Nemchenok, A. Olchevski Joint Institute of Nuclear Research, Dubna, Russia V.N. Vyrodov Kurchatov Institute, Moscow, Russia B.Y. Hsiung National Taiwan University, Taipei M. Bishai, M. Diwan, D. Jaffe, J. Frank, R.L. Hahn, S. Kettell, L. Littenberg, K. Li, B. Viren, M. Yeh Brookhaven National Laboratory, Upton, New York, U.S. R.D. McKeown, C. Mauger, C. Jillings California Institute of Technology, Pasadena, California, U.S. K. Whisnant, B.L. Young Iowa State University, Ames, Iowa, U.S. W.R. Edwards, K. Heeger, K.B. Luk University of California and Lawrence Berkeley National Laboratory, Berkeley, California, U.S. V. Ghazikhanian, H.Z. Huang, S. Trentalange, C. Whitten Jr. University of California, Los Angeles, California, U.S. M. Ispiryan, K. Lau, B.W. Mayes, L. Pinsky, G. Xu, L. Lebanowski University of Houston, Houston, Texas, U.S. J.C. Peng University of Illinois, Urbana-Champaign, Illinois, U.S. X. Guo, N. Wang, R. Wang Beijing Normal University, Beijing L. Hou, B. Xing, Z. Zhou China Institute of Atomic Energy, Beijing M.C. Chu, W.K. Ngai Chinese University of Hong Kong, Hong Kong J. Cao, H. Chen, J. Fu, J. Li, X. Li, Y. Lu, Y. Ma, X. Meng, R. Wang, Y. Wang, Z. Wang, Z. Xing, C. Yang, Z. Yao, J. Zhang, Z. Zhang, H. Zhuang, M. Guan, J. Liu, H. Lu, Y. Sun, Z. Wang, L. Wen, L. Zhan, W. Zhong Institute of High Energy Physics, Beijing X. Li, Y. Xu, S. Jiang Nankai University, Tianjin Y. Chen, H. Niu, L. Niu Shenzhen University, Shenzhen S. Chen, G. Gong, B. Shao, M. Zhong, H. Gong, L. Liang, T. Xue Tsinghua University, Beijing K.S. Cheng, J.K.C. Leung, C.S.J. Pun, T. Kwok, R.H.M. Tsang, H.H.C. Wong University of Hong Kong, Hong Kong Z. Li, C. Zhou Zhongshan University, Guangzhoz