Determining The Neutrino Mixing Angle  13 With The Daya Bay Nuclear Power Plants Kam-Biu Luk University of California, Berkeley and Lawrence Berkeley National Laboratory Seminar at BNL, November 4, 2005

Kam-Biu LukDaya Bay Experiment2 Neutrino Mixing Majorana phases Six parameters: 2  m 2, 3 angles, 1 phase + 2 Majorana phases Pontecorvo-Maki- Nakagawa-Sakata Matrix For three generations of massive neutrino, the weak eigenstates are not the same as the mass eigenstates: solar reactor  atmospheric  neutrinoless reactor  accelerator LBL accelerator LBL double-  decay Parametrize the PMNS matrix as: m12m12 m22m22 m32m32 m12m12 m22m22 m32m32 Normal hierarchy Inverted hierarchy  m 2 32  m 2 21

Kam-Biu LukDaya Bay Experiment3 Neutrino Oscillation The probability of   e appearance is given by : The probability of e  X disappearance is :

Kam-Biu LukDaya Bay Experiment4 Current Status of Mixing Parameters (  23,  m 2 32 ) (  12,  m 2 21 ) (  13,  m 2 31 )  m 2 31   m 2 32 >>  m 2 21  12 and  23 are large Unknowns ： sin 2 2  13 ， , sign of  m 2 32  m 2 32 =( )  eV 2  23  45   m 2 21 =( )  eV 2  12 =( ) 

Kam-Biu LukDaya Bay Experiment5 Current Knowledge of  13 Maltoni etal., New J. Phys. 6,122(04) Sin 2 (2  13 ) < 0.09 Sin 2 (2  13 ) < 0.18 At  m 2 31 = 2.5  10  3 eV 2, sin 2 2   < 0.15

Kam-Biu LukDaya Bay Experiment6 Some Ideas For Measuring  13 decay pipe horn absorber target p detector ++ ++ ++ Method 1: Accelerator Experiments appearance experiment: need other mixing parameters to extract  13 baseline O( km), matter effects present expensive Method 2: Reactor Experiments disappearance experiment:  e  X baseline O(1 km), no matter effects relative cheap

Kam-Biu LukDaya Bay Experiment7 Synergy of Reactor and Accelerator Experiments Δ m 2 = 2.5×10 -3 eV 2 sin 2 2  13 = 0.05 Reactor experiments can help in Resolving the  23 degeneracy (Example: sin 2 2  23 = 0.95 ± 0.01) 90% CL Reactor w 100t (3 yrs) + Nova Nova only (3yr + 3yr) Reactor w 10t (3yrs) + Nova 90% CL McConnel & Shaevitz, hep-ex/ % CL Reactor w 100t (3 yrs) +T2K T2K (5yr, -only) Reactor w 10t (3 yrs) +T2K Reactor experiments provide a better determination of  13

Kam-Biu LukDaya Bay Experiment8 Reactor  e nXXnU  For 235 U fission, for instance, where X 1 and X 2 are stable nuclei e.g Zr Ce yielding a total of 98 protons, whereas 235 U has 92 protons. That is, on average, 6 neutrons must beta decay, giving 6  e s (per ~200 MeV).  e /MeV/fisson 3 GW th generates 6 ×  e per sec

Kam-Biu LukDaya Bay Experiment9 Detection of  in liquid scintillator: Inverse  Decay   e  p  e + + n (prompt)  + p  D +  (2.2 MeV) (delayed by ~180  s)  + Gd  Gd*  +  ’s (sum = 8 MeV) (delayed by ~30  s) Time-, space- and energy-tagged signal is a good tool to suppress background events. Energy of  e is given by: E   T e+ + T n + (m n - m p ) + m e+  T e MeV keV Threshold of inverse  decay is about 1.8 MeV; thus only about 25% of the reactor  e is usable.

Kam-Biu LukDaya Bay Experiment10 -42

Kam-Biu LukDaya Bay Experiment11 How To Measure  13 With Reactor  e ? 1. Rate deficit: deviation from 1/r 2 expectation 2. Spectral distortion

Kam-Biu LukDaya Bay Experiment12 Time Variation of Fuel Composition Typically known to ~1% 235 U 238 U 239 Pu 241 Pu normalized flux times cross section (arbitrary units) E (MeV)

Kam-Biu LukDaya Bay Experiment13 Uncertainty in  e Energy Spectrum Three ways to obtain the energy spectrum: –Direct measurement –First principle calculation –Sum up anti-neutrino spectra from 235 U, 239 Pu, 241 Pu and 238 U 235 U, 239 Pu, 241 Pu from their measured  spectra 238 U(10%) from calculation (10%) Measurements agree with calculations to ~2% G ö sgen Bugey3 Measurement Best calculation Bugey3 Measurement first-principle calculation

Kam-Biu LukDaya Bay Experiment14 Background 12 B 12 N Depends on the flux of cosmic muons in the vicinity of the detector Go as deep as possible! Keep everything as radioactively pure as possible! KamLAND

Kam-Biu LukDaya Bay Experiment15 Location of Daya Bay 45 km from Shenzhen 55 km from Hong Kong

Kam-Biu LukDaya Bay Experiment16 LingAo II NPP: 2  2.9 GW th Ready by 2010 The Site Daya Bay NPP: 2  2.9 GW th LingAo NPP: 2  2.9 GW th

Kam-Biu LukDaya Bay Experiment17 Ranking of Nuclear Power Plants GW th 1. Kashiwazaki (Japan) (7) 2. Zaporozhye (Ukraine) (6) 5. Gravelines (France) (6) 6. Paluel (France) (4) 6. Cattenom (France) (4) 9. Hamaoka (Japan) (5) 11. Fukushima Daini (Japan) (4) 10. Ohi (Japan) (4) 8. Fukushima Daiichi (Japan) (6) 3. Yonggwang (S. Korea) (6) 3. Ulchin (S. Korea) (6) 12. Daya Bay-Ling Ao (China) (4+2) ~2010

Kam-Biu LukDaya Bay Experiment18 Horizontal Access Tunnels Advantages of horizontal access tunnel: - mature and relatively inexpensive technology - flexible in choosing overburden - relatively easy and cheap to add expt. halls - easy access to underground experimental facilities - easy to move detectors between different locations with good environmental control.

Kam-Biu LukDaya Bay Experiment19 A ~1.5 km-long Tunnel Onsite

Kam-Biu LukDaya Bay Experiment20 Cross Section of Tunnel For Daya Bay Experiment 1.2 m 7.2 m 0.8 m 3.2 m

Kam-Biu LukDaya Bay Experiment21 Sin 2 (   ) = 0.1  m 2 31 = 2.5 x eV 2 Sin 2 (   ) =  m 2 21 = 8.2 x eV 2 Where To Place The Detectors ? reactor near detector to measure raw flux at L 1 far detector to measure changes at L 2  e

Kam-Biu LukDaya Bay Experiment22 Where To Place The Detectors At Daya Bay? Daya Bay Ling Ao~1700 m

Kam-Biu LukDaya Bay Experiment23 Daya Bay NPP Ling Ao NPP Daya Bay Near Ling Ao Near Far site Ling Ao-ll NPP (under const.) 590 m 1175 m 570 m Possible Locations of Detector Sites Empty detectors are moved to underground halls through an access tunnel with 8% slope. Filled detectors can be swapped between the underground halls via the 0%-slope tunnels. Excess portal

Kam-Biu LukDaya Bay Experiment24 Location of Tunnel Entrance Entrance portal

Kam-Biu LukDaya Bay Experiment25 Location of Daya Near Detector

Kam-Biu LukDaya Bay Experiment26 Location of Ling Ao Near Detector

Kam-Biu LukDaya Bay Experiment27 Location of Far Detector

Kam-Biu LukDaya Bay Experiment28 A Versatile Site Rapid deployment: - Daya near site + mid site - 0.7% reactor systematic error Full operation: (1) Two near sites + Far site (2) Mid site + Far site (3) Two near sites + Mid site + Far site Internal checks, each with different systematic

Kam-Biu LukDaya Bay Experiment29 What Target Mass Should Be? Systematic error (per site): Black : 0.6% Red : 0.25% Blue : 0.12% Solid lines : near+far Dashed lines : mid+far DYB: B/S = 0.5% LA: B/S = 0.4% Mid: B/S = 0.1% Far: B/S = 0.1%  m 2 31 = 2  eV 2

Kam-Biu LukDaya Bay Experiment30 Conceptual Design of Detector Modules Three-layer structure: I. Target: Gd-loaded liquid scintillator II. Gamma catcher: liquid scintillator, 45cm III. Buffer shielding: mineral oil, ~45cm Possibly with diffuse reflection at ends. For ~200 PMT’s around the barrel: buffer 20t Gd-doped LS gamma catcher 40 t

Kam-Biu LukDaya Bay Experiment31 ~350 m ~97 m ~98 m ~208 m Cosmic-ray Muon Apply the Geiser parametrization for cosmic-ray flux at surface Use MUSIC and mountain profile to estimate muon flux & energy DYBLingAoMidFar Elevation (m) Flux (Hz/m 2 ) Mean Energy (GeV) near site far site

Kam-Biu LukDaya Bay Experiment32 Conceptual 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 strips or RPCs Combined efficiency of Cherenkov and tracker > 99.5% detector module PMTs Tracker rock

Kam-Biu LukDaya Bay Experiment33 Alternative Design 40t-3 layer module top of water pool

Kam-Biu LukDaya Bay Experiment34 Background Inside Detector Two classes of background: 1.Uncorrelated: Accidental ─ random coincidence of two unrelated events appear close in space and time. : 2.Correlated: Fast neutron ─ a fast spallation neutron gets into the detector, creates a prompt signal (knock-out proton), thermalizes and is captured. Cosmogenic isotopes Cosmogenic isotopes ─ 9 Li and 8 He with β- n decay modes are created in spallation of μ with 12 C. The decays mimic the antineutrino signal.

Kam-Biu LukDaya Bay Experiment35  - n Decay Of 8 He And 9 Li Correlated final state: β +n+2 α Correlated final state: β +n+ 7 Li τ ½ = 178 ms 49.5% Correlated τ ½ = 119 ms 16% Correlated

Kam-Biu LukDaya Bay Experiment36 Background Near SiteFar Site Radioactivity (Hz)<50 Accidental B/S<0.05% Fast Neutron background B/S0.15%0.1% 8 He/ 9 Li B/S0.55%0.25% Use a modified Palo-Verde-Geant3-based MC to model response of detector. Cosmogenic isotopes: 8 He/ 9 Li which can  -n decay - Cross section measured at CERN (Hagner et. al.) - Can be measured in-situ, even for near detector with muon rate ~ 10 Hz. The above number is before shower-muon cut which can further reduce cosmogenic background. 20t module

Kam-Biu LukDaya Bay Experiment37 Detector Systematic Issues Potential sources of systematic uncertainty are: detector efficiency gadolinium fraction (neutron detection efficiency) target mass target chemistry: fraction of free proton (target particle) in terms of hydrogen/carbon trigger efficiency cut efficiency live time surprises at the 0.01 level

Kam-Biu LukDaya Bay Experiment38 Possible Solutions Relative detector efficiency Calibrate all detectors with the same set of radioactive sources. Gd fraction (i) Control synthesis of liquid scintillator (ii) Measure the Gd- to H-capture ratio Target mass (i) Use the same batch or equally splitting batches of liquid scintillator, and measure flow rates (ii) Use  e events to cross calibrate, implying moving detectors.

Kam-Biu LukDaya Bay Experiment39 Detector Systematic Uncertainties per module absolute measurements relative measurement %

Kam-Biu LukDaya Bay Experiment40 Topography survey: Completed Geological Survey: Completed Verified topographic information Generated new map covering 7.5 km 2 Geological Physical Survey: Completed High-resolution electric resistance Seismic Micro-gravity Bore-Hole Drilling: November-December, 2005 Geotechnical Survey raw data

Kam-Biu LukDaya Bay Experiment41 Daya Bay NPP Ling Ao NPP Daya Bay Near 360 m from Daya Bay Overburden: 97 m Far site 1600 m from Lingao 1900 m from Daya Overburden: 350 m Ling Ao-ll NPP (under const.) 8% slope 672 m (12% slope) Ling Ao Near 500 m from Lingao Overburden: 98 m Mid site ~1000 m from Daya Overburden: 208 m Total length: ~3200 m

Kam-Biu LukDaya Bay Experiment42 Daya Bay siteDaya Bay site - baseline = 360 m - baseline = 360 m - target mass = 40 ton - target mass = 40 ton - B/S = ~0.5% - B/S = ~0.5% LingAo siteLingAo site - baseline = 500 m - baseline = 500 m - target mass = 40 ton - target mass = 40 ton - B/S = ~0.5% - B/S = ~0.5% Far siteFar site - baseline = 1900 m to DYB cores - baseline = 1900 m to DYB cores 1600 m to LA cores 1600 m to LA cores - target mass = 80 ton - target mass = 80 ton - B/S = ~0.2% - B/S = ~0.2% Three-year run (0.2% statistical error)Three-year run (0.2% statistical error) Detector residual error = 0.2%Detector residual error = 0.2% Use rate and spectral shapeUse rate and spectral shape 90% confidence level Sensitivity of sin 2 2  13 Sept, near + far near (40t) + mid (40 t) 1 year

Kam-Biu LukDaya Bay Experiment43 Precision of  m 2 31 sin 2 2  13 = 0.02 sin 2 2  13 = 0.1

Kam-Biu LukDaya Bay Experiment44 Gd-loaded Liquid Scintillator It can significantly reduce backgrounds (short capture time, high capture energy) Problems: (a) doping Gd into organic LS from inorganic Gd compound and achieve Light yield = 55% of anthracene Att. length = 11m (b) Aging Palo Verde: 0.03%/day Chooz: 0.4%/day

Kam-Biu LukDaya Bay Experiment45 Synthesis of Gd-loaded Liquid Scintillator Investigating a few candidates at IHEP: Date Gd (%) One candidate: - 0.1% Gd (D2EHP-ligand) in 20% mesitylene-80% dodecane - Light yield: 91% of pure LS - attenuation length = 6.2 m - stable for more than two months: - no effect on acrylic R&D collaborative effort at BNL: - Gd (carboxylate ligands) in PC and dodecane - all stable for almost a year

Kam-Biu LukDaya Bay Experiment46 Prototype Detector at IHEP Constructing a 2-layer prototype with 0.5 t Gd-doped LS enclosed in 5 t of mineral oil, and 45 8” PMTs to evaluate design issues at IHEP, Beijing Steel tank acrylic vessel PMT mount Front-end board (version 2)

Kam-Biu LukDaya Bay Experiment47 Installing proptubes in Sept, 2005 The Aberdeen Tunnel Experiment Study cosmic muons & cosmogenic background in Aberdeen Tunnel, Hong Kong. similar geology between Aberdeen and Daya Bay Overburden ~ Daya Bay sites

Kam-Biu LukDaya Bay Experiment48 Precision Measurement of  12 and  m 2 21

Kam-Biu LukDaya Bay Experiment49 Precise Measurement of  12 Large-amplitude oscillation at ~55 km due to  12 Near detectors close to reactors 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 of  12 Sin 2 (   ) = 0.1  m 2 31 = 2.5 x eV 2 Sin 2 (   ) =  m 2 21 = 8.2 x eV 2 Since reactor  e are low-energy, it is a disappearance experiment: KamLAND

Kam-Biu LukDaya Bay Experiment50 Tai Mo Shan (957 m) ~55 km Daya Bay NPP Hong Kong Shenzhen Location of Hong Kong Site For  12 Measurement

Kam-Biu LukDaya Bay Experiment51 Precision of  12 With The Daya Bay Facility Inputs: Thermal power = 17.4 GW Baseline = 55 km Target mass = ~ 500 ton LS Mixing parameters: sin 2 2  12 = sin 2 2  13 = 0.1  m 2 12 = 8.2  eV 2  m 2 13 = 2.5  eV 2

Kam-Biu LukDaya Bay Experiment52 Summary and Prospects 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 sin 2 2  13. The three Chinese funding agencies are discussing cost-sharing of a request of RMB$200 million. The US team is waiting for the NuSAG’s decision. Will complete detailed design of detectors, tunnels and underground facilities in Plan to commission the Fast Deployment scheme in , and Full Operation in Welcome more collaborators to join.

Kam-Biu LukDaya Bay Experiment53 What Have We Learned From Chooz? CHOOZ Systematic Uncertainties Reactor  flux & spectrum Detector Acceptance 2% 1.5% Total 2.7% 5 t Gd-loaded liquid scintillator to detect L = 1.05 km D = 300 mwe P = 8.4 GW th Rate: ~5 evts/day/t (full power) including bkg/day/t  e + p  e + + n e + + e -  2 x MeV  n + Gd  8 MeV of  s;  ~ 30  s ~3000  e candidates (included 10% bkg) in 335 days