Richard L. (Dick) Hahn

1. Two Proposals to Measure Theta-13 with Antineutrinos: at the Braidwood (USA) and Daya Bay (PRC) Reactors Richard L. (Dick) Hahn Solar-Neutrino & Nuclear-Chemistry Group * Chemistry Department, BNL Upton NY 11973, USA *Research sponsored by the Office of Nuclear Physics, U.S. Department of Energy 27th Erice School of Nuclear Physics, September 16-24, 2005

2. 40 Years of BNL Chemistry and Neutrinos • HOMESTAKERadiochemical Detector • 615 tons of C2Cl4; 37Cl + ne 37Ar+ e- (~40 years) • GALLEX Radiochemical Detector • 30 tons of Ga; 71Ga + ne 71Ge + e- (1986 - 1998) • SNO Water ČerenkovReal-time Detector • 1000 metric tons of ultra-pure D2O (1996 -  2006) • LENS Real-time Detector(R&D) • 115In in Liquid Scintillator (~2000 - now) • BNL-AGS NEUTRINO FACTORY • Very Long-Baseline Experiment - Neutrino Beam from BNL (~2002 - now) • THETA-13 New High-Precision Experiments at Nuclear Reactors Real-timeAntineutrino Detector(R&D) • Gd in Liquid Scintillator (~2003 - now)

3. ? 13 yet to be measured determines accessibility to CP phase No good ‘ad hoc’ model to predict 13. Neutrino Mixing UMNSP Matrix SNO, solar SK, KamLAND reactor and accelerator atmospheric, K2K 0 13 = UNKNOWN, < 11°, from CHOOZ 23 = ~ 45° 12 ~ 32°

4. KamLAND in 2003:First Direct Evidence for Reactor eDisappearance 50 Years of Reactor Neutrino Physics 1953 First reactor neutrino experiment 1956“Detection of Free Antineutrino”, Reines and Cowan  Nobel Prize in 1995 2003 KamLAND’s observation of e disappearance Past Experiments Hanford Savannah River ILL, France Bugey, France Rovno, Russia Goesgen, Switzerland Krasnoyark, Russia Palo Verde Chooz, France Reactors in Japan PRL 90:021802 (2003) Observed e54 events No-Oscillation 86.8 ± 5.6 events Background 1 ± 1 events Livetime: 162.1 ton-yr

5. KamLAND in 2004: Evidence of Spectral Distortion in Energy Spectrum (adds substantial information) 138d,  210Pb 210Bi 210Po 206Pb 13C(,n)16O hep-ex/0406035 (2004) Observed e258 events No-Oscillation 365.2 ± 23.7 (syst.) Background 17.8 ± 7.3 events Livetime: 766.3 ton-yr Future Reduce systematic error with improved calibrations. Reduce 210Pb, lower analysis threshold, search for geo-neutrinos. Spectral Distortions: A unique signature of neutrino oscillation! Simple, rescaled reactor spectrum is excluded at 99.6% CL(χ2=37.3/18)

6. e e e Measuring 13 with Reactor Antineutrinos Precision Oscillation Measurement as a Function of Distance from Source Relativeeflux measurement at different distances with Identical Detectors. 13 Diablo Canyon 0.5-2 km nuclear reactor Event rate:~1 event/GW/ton/day at 1km underground scintillator  detectors, ~40-120t Projected sensitivity: sin2213  0.01

7. General Design for q13 ~1% Sensitivity • Power station ~ several GW output • Multiple Movable (“interchangeable”) Detectors: each ~50-100 tons of liquid scintillator. ~ 450 m.w.e. or more overburden • Horizontal distance from the reactor vessel to detectors - “near” ~200 m (with no oscillations) and “far” ~1500-2000 m (maximum for oscillations) • Crucial aspect: Comparison of near and far data eliminates many experimental “unknowns” and systematic errors

8. e+ Liquid Scintillatorwith Gadolinium e = Photomultiplier Tube n Experimental Setup • The reaction process is inverse β-decay followed by neutron capture • Delayed coincidence signal is crucial for background reduction. • Positron energy implies the neutrino energy Eν = Evis + 1.8 MeV – 2me • The scintillator will be doped with gadolinium to enhance n-capture;  = 40000 barns. Shielding 6 meters nmGd → m+1Gdg’s (8 MeV)

9. Reconstructed Positron Energy Reconstructed NeutronCapture Energy Detector Response Energy spectra Measure (1) positron event rate (2) energy spectrum (and spectral distortion)

10. Estimated Braidwood Backgrounds at 450mwe Experimental Challenges for Precision Multi-Detector Disappearance Exp’ts. • Are the Detectors Identical? Fiducial VolumeAcceptance Energy scale and linearity Deadtime • BackgroundsUncorrelated Backgrounds • ambient radioactivity • accidentals Correlated Backgrounds • cosmic rays induce neutrons in the surrounding rock and buffer region of the detector • cosmogenic radioactive nuclei that emit delayed neutrons in the detector, e.g. 8He (T1/2=119ms), 9Li (T1/2=178ms)

11. 8He/9Li Background

12. A reactor experiment is prime and unambiguous technique to measure q13 q13 is an important physics parameter Needed to constrain the models of lepton mixing matrix If very small, probably indicates a new symmetry q13 is key for planning the future long-baseline experiments to measure CP violation and the mass hierarchy Consensus Recommendation 1) An expeditiously deployed multi-detector reactor experiment with sensitivity … sin22q13=0.01 … 2) A timely accelerator experiment with comparable … sensitivity … 3) A proton driver … with an appropriate very large detector … Funding agencies now working towards implementing the plan  NuSAG… Importance of q13 2004 (2004)

13. Huber et al

14. Proposed Reactor Oscillation Experiments

15. Braidwood Braidwood Experiment • Braidwood Setup: • Two 3.6 GW reactors • Two 65 ton (fid vol) near detectors at 270 m • Two 65 ton (fid vol) far detectors at 1510 m • Flat overburden • 180m shafts and detector halls at • same depth, 450 mwe

16. Braidwood Reactor Collaboration

17. Braidwood Design Principles Compare rate/shape in identical, large, spherical, on-axis detectors at two distances that have equal overburden shielding. (Multiple detectors at each site: two near and two far)Systematic uncertainties cancel to first order and only have uncertainties for second order effects • Detectors filled simultaneously with common scintillator on surface • Large (65 tons fiducial) detectors give large data samples • Spherical detectors reduce any geometrical effects from neutrino direction and reconstruction • On-axis detectors eliminate any dependence on reactor power variations in a multi-reactor setup. • Equal overburden shielding gives equal spallation rates in near and far sites that can be exploited for detector and background checks

18. Civil Construction • Two detector locations at 200 m and 1500 m from the reactors • A 10 m diameter vertical shaft allows access to the detector caverns at 183 m below the surface • Caverns are 12m x 14m x 32m and house two detectors with their veto systems • Detectors are co-filled on the surface giving much less radon contamination

19. Staging & Assembly Area Braidwood Reactors Connecting road Far Site Near Site PMT staging & test Acrylic Tank Assembly Outer ShellAssembly Area  Off to shaft Final Assembly Area PMT Installation Oil Storage Area Staging & Assembly Area

20. Bore Hole Project at the Exelon Site Bore hole project completed in January 2005 • Bore holes drilled to full depth (200m) at near and far shaft positions at Braidwood site. • Provided detailed information on geology, ground water, radioactivity, etc. • Confirmed feasibility of detectors down to depths of 460mwe. • Demonstrated willingness of Exelon Reactor Co. to allow construction on their site.

21. Detector Design and Engineering • Engineering by: Argonne, FermiLab and Bartoszek & Associates • Baseline design has: • Outer steel buffer oil containment vessel (7m diameter) • 1000 low activity glass PMTs mounted on inside surface • Inner acrylic Gd-Scint containment vessel (5.2m diameter) • Top access port can be used to insert calibration sources

22. Transport is necessary to move detectors from construction/filling area to below ground halls Moving also required for cross checks, “swapping” Example scenario: Use system with cable to lift, put units on multi-wheeled trailer Movable Detectors A B A C B D A D B C Goldhofer Trailer Moving 400 tons

23. Experiment Setup and Rates

24. 90% CL Sensitivity vs. Years of Data • Information from both counting and shape fits • Combined sensitivity for sin22q13 reaches the 0.005 level after three years

25. Braidwood Schedule • 2004: R&D proposal submission. • 2004: Bore hole project completed on Braidwood site. • 2005: NuSAG review • 2006: Full proposal submission • 2007: Project approval; start construction • 2010: Start data collection

26. Powerful e Source: Multiple reactor cores. (4 units 11.6 GW Eth, eventually 6 units 17.4 GW Eth ) Shielding from Cosmic Rays: Up to 1200 mwe overburden nearby. Infrastructure: Construction roads. Controlled access. Daya Bay Nuclear Power Plant

27. Daya Bay Collaboration Beijing Normal University Brookhaven National Laboratory California Institute of Technology China Institute of Atomic Energy Chinese University of Hong Kong Institute of High Energy Physics, Beijing Iowa State University Joint Institute for Nuclear Research Cooperation of Chinese Nuclear Power Company Lawrence Berkeley National Laboratory Nankai University Tsing Hua University University of California at Berkeley University of Hong Kong University of Maryland University of Illinois at Urbana-Champaign University of Science and Technology of China

28. 40t target mass Daya Bay Nuclear Power Plant • Laboratory with Horizontal Tunnels • - Simplifying logistics: Build detectors outside before moving into tunnel. • Swapping detectors: Eliminates most systematic errors. Helps understand backgrounds. • Modular detectors: Phased approach, allowing rapid deployment, different configurations, and cross-calibration. • Optimizing distance to reactors: Flexibility of detector position. Multiple reactors at different sites.

29. Site Reactor e Signal (/day) near 1160 mid 464 far 116 Not a rare event experiment! Tunnel Layout at Daya Bay FAR SITE overburden ~1143 mwe distance to Daya Bay 2227 m distance to Ling Ao 1801 m Ling Ao NEAR SITE overburden ~330 mwe distance to Ling Ao 500 m distance to Daya Bay 1368 m Ling Ao ll (under construction) MID SITE overburden ~560 mwe distance to Daya Bay 1111 m distance to Ling Ao 796 m Ling Ao Daya Bay NEAR SITE overburden ~330 mwe distance to Daya Bay 500 m distance to Ling Ao 807 m Daya Bay

30. Development of Multi-Layer Cylindrical Detector Modules ~600 externally mounted PMTs 12% PMT coverage ~40cm of mineral oil buffer to reduce backgrounds Liquid scintillator (gamma catcher) e+p  e++n integrated calibration systems Liquid scintillator + Gd ~40 ton fiducial volume Electronics • movable over a distance of ~2km

31. Movable Detector Modules in Underground Halls Swapping: Cancellation of systematics Side-by-Side Calibration: Initial side-by-side calibration at near site Cross-Check of Modules

32. Muon Flux Underground

33. Example of Passive Shielding: Sand or Water muon Active muon tracker + passive shielding + inner liquid scintillator detector Cherenkov or H20 Scint. H2O or concrete option 2 option 1 Muon System and Passive Shielding • Requirements • Excellent muon tagging/tracking • Low muon rates to measure muon-induced 9Li spectrum. • >2m water shielding around detector against neutrons.

34. Staged Approach: Phase I Running 40 t 2 40 t 1 Illustration K. Chow

35. Staged Approach: Phase II Running 120 t 80 t Illustration K. Chow

36. Staged Approach: Phase III Running 120 t 40 t 40 t Illustration K. Chow

37. Sensitivity Scenario Total Tonnage (t) near1/near2/mid/far near/mid 40-0-40-0 mid/far 0-0-80-120 near/far 40-40-0-120 3 year mid/far Chooz 1 year near/mid commissioning Chooz July 2007 Start of data taking at near and mid sites 2009 First result based on near and mid sites. Start of data taking at far site. 2010 First result based on data from far site 3 year near/far 1 year comm 3year mid/far Chooz 3 year near/far

38. The Role of the BNL Chemistry Neutrino Group in these U.S. q13 Experiments • We are involved in both Braidwood and Daya Bay. • Reason: Previous experiments had serious problems with the stability of their Gd-LS; Chooz had to shut down, Palo Verde had some deterioration of the signal. • Common Task: Our main role is development of the ~0.1% Gd-LS for the e+ - neutron delayed coincidence. Is logical development from our LENS R&D (In ~ 10% w/w). • Additional questions: (a) control and assay of impurities, chemical and radioactive, (b) compatibility of different LS with detector vessel (acrylic?)…

39. light yield is a function of PC% • 1.2% Gd-LS is ~81% of PC • 0.2% Gd-LS is > 95% of PC Light Yield: a Function of PC PC = pseudocumene = trimethylbenzene

40. 0.2% Gd in 20% PC-80% Dodecane Optical spectrophotometer with 10-cm cell

41. Gd-LS Stability New: from 10 cm cell  100 cm (blue laser) and 200 cm (LEDs) cells

42. Funding Future in the U.S.? • In Spring 2005, NSF and DOE jointly requested that HEPAP and NSAC jointly form a special review panel, NuSAG, the Neutrino Science Advisory Group • Purpose: To review the two main areas recommended by the 2004 Neutrino Study, Double Beta Decay and Theta-13, and make recommendations in a matter of a few months • Theta-13 oral presentations (Braidwood, Daya Bay, Double Chooz) made to NuSAG in June 2005 • Written replies to NuSAG questions/comments in July

43. Funding Future in the U.S.? • Similar schedule followed for Double Beta Decay • NuSAG issued its recommendations about Double Beta Decay in early September. Supported 3/5 proposals for further R&D • Expectation: NuSAG will make decisions about Theta-13 R&D in the next few months, will issue recommendations before the end of this year

44. Conclusions About q13 • Proponents say, “A reactor experiment is the only unambiguous measurement of q13.” • It is “the next obvious neutrino experiment to do.” • q13 is a important physics parameter, which is key for planning future long-baseline experiments to measure CP violation and the mass hierarchy. • Reactor experiments are being pursued at many sites and (we hope that) it is “likely” that more than one will be approved and go forward.

45. The End