The Daya Bay Reactor Neutrino Experiment Jonathan Link Virginia Tech

1. The Daya Bay Reactor Neutrino Experiment Jonathan Link Virginia Tech On behalf of the Daya Bay Collaboration October 20, 2011

2. From Bemporad, Gratta and Vogel Arbitrary Observable ν Spectrum Cross Section Flux Nuclear Reactors as a Neutrino Source Nuclear reactors are a very intense sources of νe coming from the b-decay of the neutron-rich fission fragments. A typical commercial reactor, with 3 GW thermal power, produces 6×1020νe/s The observable ne spectrum is the product of the flux and the cross section. Jonathan Link, Virginia Tech Seminar

3. Reactor Neutrino Event Signature nep→ e+n ncapture The reaction process is inverse β-decay (Used by Reines and Cowan in the neutrino discovery experiment) Two part coincidence signal is crucial for background reduction Minimum energy for the primary signal is 1.022 MeV from e+e−annihilation at threshold Positron energy implies the anti-neutrino energy Neutron capture on Gd provides a secondary burst of light approximately 30 μs later Eν = Ee + 0.8 MeV ( =mn-mp+me-1.022) Jonathan Link, Virginia Tech Seminar

4. Reactor Oscillation Experiment Basics νe νe νe νe νe νe νe νe νe νe νe νe Oscillations observed as a deficit of νe Unoscillated flux observed here sin22θ13 πEν/2Δm213 Well understood, isotropic source of electron anti-neutrinos Detectors are located underground to shield against cosmic rays. 1.0 Probability νe Distance (L/E) ~1800 meters (at 3 MeV) Jonathan Link

5. Located in Guangdong Province, China, about one hour from Hong Kong. 6 reactors on site for a total of 17.4 GW of thermal power. It is among the most powerful nuclear power plants in the world The mountainous terrain is well suited for shielding underground detectors The utility company (China Guangdong Nuclear Power Group) has joined the collaboration The Daya Bay Nuclear Power Plant Jonathan Link

6. Daya Bay Design Principles Identical near and far detectorscancel many systematic error. Multiple modulesboost statistics while reducing systematic errors with multiple independent measurements and direct comparisons of detector counting rates in a common ν flux. Three zone detector designeliminates the need for spatial cuts which can introduce systematic uncertainties. Shielding from cosmic rays and natural radioactivity reduces background rates and provides measurable handles on remaining background. Movable detectorsallows for concurrent civil and detector construction, early detector commissioning at the near site, and possible cross calibration between near and far detectors to further reduce systematic errors. Jonathan Link

7. Experimental Setup Total tunnel length ~ 3000 m Far site Overburden: 355 m 900 m Ling Ao Near Overburden: 112 m Filled detectors are transported between halls via horizontal tunnels. 465 m Ling Ao II Reactors Water hall (Starting 2011) Construction tunnel 810 m Ling Ao Reactors Liquid Scintillator hall 295 m Entrance Daya Bay Near Overburden: 98 m Daya Bay Reactors

8. Experimental Setup • 8 identical anti-neutrino detectors (two at each near site and four at the far site) to cross-check detector efficiency • Two near sites sample flux from reactor groups Far site Overburden: 355 m 9 different baselines Ling Ao Near Overburden: 112 m Ling Ao II Reactors (Starting 2011) Ling Ao Reactors Halls Reactors Daya Bay Near Overburden: 98 m Daya Bay Reactors

9. The Daya Bay DetectorDesign Mineral Oil LS Gd-Loaded LS (20 tons) 1.55 m 1.99 m 5 meters 2.49 m • Three zone, cylindrical design • 0.1% wt Gd-Loaded LS target • LS gamma catcher • Mineral oil buffer • Reflectors at top and bottom • 196 PMT’s arrayed around the barrel of the cylinder • 5 meter total diameter • Designed to sit in a pool of ultrapure water Jonathan Link

10. The Daya Bay DetectorDesign Jonathan Link

11. Water Shield and Muon Tagging System RPCs Water Pool The water pool shields the detectors from energetic γ-rays from the decay chains of 238U, 232Th and 40K in surrounding the rock It also detects the Čerenkov light produced by cosmic ray muons which pass near the detectors The pool is lined with white Tyvek and sparsely populated with PMTs The pool is optically separated into two zones (inner and outer) The two zones allow a better measurement of efficiency The top is covered with 4 layers of RPC Minimum 2.5 m water shielding in all directions. Jonathan Link

12. Water Shield and Muon Tagging System Jonathan Link

13. in air in water Water Controls Radioactive Backgrounds Singles events verses height in the partially filled pool show the suppression of radioactive backgrounds by water. Jonathan Link

14. Filled Water Pool in First Near Hall Jonathan Link

15. Completed Near Hall Ready for Data Taking Jonathan Link

16. p n n m m Muon Induced Correlated Backgrounds Tag muons that pass near the detectors. Range out fast neutrons from muons that are further away. Jonathan Link

17. MuonSpallation Backgrounds 9Li Antineutrino Rate Isotopes like 9Li and 8He are produced in the detectors in the spallation of 12C nuclei by muons. 9Li and 8He decay with half-lives of tenths of seconds to β+n. Can be identified by their time correlation with muons in the detector. Jonathan Link

18. Signal to Background (a) (1%) (d) (c) (b) After all filters the background rates are small compared to a disappearance due to oscillations with sin22θ13 of 1%. In addition, each background has a characteristic and distinct energy spectrum. Jonathan Link

19. Measuring sin22θ13 Proton Number Ratio sin22θ13 Ratio of Detector Efficiencies Calibration ±0.2% ±0.3% The measurement is a ultimately a ratio of observed inverse β-decay events in near and far detectors in initially one, but ultimately many energy bins (sampling a broad range of oscillation phases). Jonathan Link

20. Systematic and Statistical Errors Jonathan Link

21. Sensitivity Jonathan Link

22. Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of 8 detectors completed • August 2011: Hall 1 data taking begins • Detector installation underway in hall 2 Jonathan Link

23. Installation in Second Near Hall Jonathan Link

24. Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of 8 detectors completed • August 2011: Hall 1 data taking begins • Detector installation underway in hall 2 • Muon system installation underway in hall 3. Jonathan Link

25. Muon Installation in the Far Hall Jonathan Link

26. Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of 8 detectors completed • August 2011: Hall 1 data taking begins • Detector installation underway in hall 2 • Muon system installation underway in hall 3. • Summer 2012: Start of data with full installation • Three years of data taking to reach sensitivity goal. Jonathan Link

27. The Daya Bay Collaboration Europe.: Charles U., JINR, Kurchatov Institute Asia: Beijing Normal, Chengdu U. of Tech., CGNPE, CIAE, CUHK, Dongguan Polytech, IHEP Beijing, Nankai, Nanjing, National Chiao-Tung U., National Taiwan U., National United U., Shangdong U., SJTU, Shenzhen U., Tsinghua U., HKU, USTC, Zhongshan U. U.S.: BNL, Caltech, Cincinnati, George Mason, Houston, IIT, Iowa State, LBNL, Princeton, RPI, UC Berkeley UCLA, UIUC, Virginia Tech, William and Nary, Wisconsin