1. 12 December 2003APS Neutrino StudyE. Blucher APS Neutrino Study: Reactor Working Group What can we learn from reactor experiments? Future reactor experiments to measure sin 2 2  13 Ongoing activities Specific goals of study Group Leaders: Gabriela Barenboim, Ed Blucher

2. Long history of neutrino experiments at reactors Current interest is focused mainly on possibility of measuring   (from SJF) (Study will evaluate other physics possibilities also) 20 m KamLAND 6 m CHOOZ

3. Reactor Measurements of Future: Search for small oscillations at 1-2 km distance (corresponding to Reactor experiments allow direct measurement of sin 2 2   : no matter effects, no CP violation, almost no correlation with other parameters. Sensitivity goal: sin 2 2   ~0.01. Level at which long-baseline “superbeams” can be used to measure mass hierarchy,CPV; ~ sensitivity goal of proposed accel. expts. Distance to reactor (m) P ee

4. Previous Reactor   Experiments CHOOZ and Palo Verde Experiments –Single detector experiments –Detectors used liquid scintillator with gadolinium and buffer zones for background reduction –Shielding: CHOOZ: 300 mwe Palo Verde: 32 mwe –Fiducial mass: CHOOZ: 5 tons @ 1km, 5.7 GW –~2.2 evts/day/ton with 0.2-0.4 bkg evts/day/ton –~3600  events Palo Verde: 12 tons @ 0.85km, 11.6 GW –~7 evts/day/ton with 2.0 bkg evts/day/ton –~26000  events CHOOZ Systematic Errors (from M. Shaevitz)

5. CHOOZ Target: 5 ton Gd-doped scintillator

6. Is it possible to improve the Chooz experiment by order of magnitude (i.e., sensitive to sin 2 2   ~ 0.01)? Add second detector; bigger detectors; better control of systematics. ~200 m~1500 m What systematic error is attainable? Efficiency and energy calibration strategy (movable detectors?) Backgrounds Multiple reactor cores Site / depth Choice of scintillator (stability of Gd-loaded scintillator) Size, distance of detectors

7. Analysis Using Counting and Energy Spectrum (Huber et al. hep-ph/0303232) Counting exp. region Spectrum & Rate region (12 ton det.)(250 ton det.) 90%CL at  m 2 = 3×10 -3 eV 2  cal relative near/far energy calibration  norm relative near/far normalization Scenarios: Reactor I = 12ton×7GW×5yrs Reactor II = 250ton×7GW×5yrs

8. Worldwide interest in two-detector reactor experiment Workshops: Alabama, June 2003 Munich, October 2003 Niigata, Japan, March 2004 Based on early workshops, a whitepaper describing physics possibilities of reactor experiment is being assembled. Excellent starting point for this study. (Maury Goodman (ed.) will speak about the white paper during tomorrow’s working group session.)

9. Sites under discussion: Kraznoyarsk (Russia) Chooz (France) Kashiwazaki (Japan) Diablo Canyon (California) Braidwood, Byron (Illinois) Wolf Creek (Kansas) Brazil Taiwan China

10. Ref: Marteyamov et al, hep-ex/0211070 Reactor Detector locations constrained by existing infrastructure Features - underground reactor - existing infrastructure ~20000 ev/year ~1.5 x 10 6 ev/year Kr2Det: Reactor  13 Experiment at Krasnoyarsk

11. Kashiwazaki - 7 nuclear power stations; world’s most powerful reactors - requires construction of underground shaft for detectors near far Kashiwazaki-Kariwa Nuclear Power Station Proposal for Reactor  13 Experiment in Japan

12. The Chooz site, Ardennes, France … Double-CH  13  13 Z …

13. CHOOZ-Far detector 7 m 3.5 m Existing CHOOZ tub

14. U.S. Nuclear Power Plants

15. Braidwood, Illinois 7.17 GW Located 24 miles southwest of Joliet.

16. Powerful: Two reactors (3.1+ 3.1 GW E th ) Overburden: Horizontal tunnel could give 800 mwe shielding Infrastructure: Construction roads. Controlled access. Close to wineries. Diablo Canyon Nuclear Power Plant 1500 ft 2 underground detectors

17. Challenge of study: How do we put together the wide array of experimental opportunities into a coherent, rich program that makes best use of limited resources? (What is most (cost) effective sequence of experiments?) Primary goal of working group is to provide input needed for this exercise. Clear statement of physics potential of reactor experiments Understand physics reach, cost, and timescale for different scenarios (e.g., fixed 10-ton detectors, fixed/movable 50-ton detectors, multiple far detectors, “best” experiment) For each scenario, describe defensible strategy for reaching the claimed systematic uncertainty. Complete rough systematic table for different scenarios with common ground rules. How do these scenarios complement and compete with other reactor and accelerator experiments around the world?