Latest Results on Electron-antineutrino Disappearance at Daya Bay Kam-Biu Luk University of California, Berkeley And Lawrence Berkeley National Laboratory On Behalf of the Daya Bay Collaboration Seminar at Imperial College/UCL, 14 June 2012
Discoveries of Neutrino Oscillation Theoretical Predictions 1 SNU = 10 -36 interaction/atom/s 2
Neutrino Mixing • Neutrino flavour eigenstates ≠ Mass eigenstates ⇓ Inverted Normal Neutrino Mixing hierarchy hierarchy 2 2 m 3 m 2 $ ' $ U e1 U e2 U e3 ' $ ' ν e ν 1 & ) & ) & ) 32 2 Δ m 2 m 1 U µ 1 U µ 2 U µ 3 ν µ = ν 2 & ) & ) & ) 2 m 2 & ) & ) & ) U τ 1 U τ 2 U τ 3 ν 3 ν τ 21 % ( % ( % ( Δ m 2 2 2 m 3 m 1 Pontecorvo-Maki- Nakagawa-Sakata Matrix Which one ? ⇓ $ ' sin θ 13 e − i δ $ ' $ ' cos θ 12 sin θ 12 0 cos θ 13 0 1 0 0 & ) & ) & ) − sin θ 12 cos θ 12 0 0 1 0 0 cos θ 23 sin θ 23 & ) & ) & ) & ) & ) & ) − sin θ 13 e i δ 0 0 1 0 cos θ 12 0 − sin θ 23 cos θ 23 % ( % ( % ( θ 13 and δ ? θ 23 ≈ 42 °± 3 ° θ 12 = 33 °± 1 ° 2 = Δ m 32 2 ± Δ m 21 2 ≈ Δ m 32 2 = (2.45 ± 0.09) × 10 − 3 eV 2 • Mass-squared differences: Δ m 31 (7.6 ± 0.2) × 10 -5 eV 2 New J. Phys. 13 (2011)063004 3
� Significance of Knowing θ 13 • Complete the determination of the mixing matrix - guide model-building • Determine ν e fraction of ν 3 ? reduce theoretical uncertainties in predicting phenomena Fraction of δ excluded at 3 σ for sin δ = 0 • θ 13 is the gateway to CP violation in the neutrino sector: " P( ν µ → ν e ) – P( ν µ → ν e ) ∝ sin2 θ 13 cos θ 13 sin δ 4
Some Approaches For Measuring θ 13 • Accelerator-based ν e appearance experiments far " target ! horn ! near ! decay pipe ! absorber ! detector ! detector ! p ! π + ! µ + ! π + ! " % 2 L µ e = sin 2 2 θ 13 sin 2 2 θ 23 sin 2 Δ m 31 2 ,matter effect) P ' + terms( δ , Δ m 32 $ 4 E ν # & - Baseline O(100-1000 km) , large detectors - Some ambiguities exist in extracting a value for θ 13 - MINOS, NOvA, T2K, … • Reactor-based ν e disappearance experiments $ ' $ ' 2 L 2 L ee ≈ 1 − sin 2 2 θ 13 sin 2 Δ m 31 ) + cos 4 θ 13 sin 2 2 θ 12 sin 2 Δ m 21 P & & ) 4 E ν 4 E ν % ( % ( - Baseline O(1 km), no matter effect, small detectors - Daya Bay, Double Chooz, RENO 5
Knowledge of θ 13 Circa March 2012 PRL 107, 041801 (2011) PRL 107 , 181802 (2011) 0 LEM > 0.8 20 Bins Merged for Fit Some hints of Events 15 MINOS a non-zero θ 13 10 T2K 5 0 2 4 6 8 Reconstructed Energy (GeV) Solar + KamLAND original flux reeval. flux PRL 108 , 131801(2012) T2K normal hier. MINOS inverted hier. Double Chooz Double Chooz Far-detector only 0 0.05 0 . 1 0 . 15 0 . 2 0 . 25 0 . 3 0 . 35 sin 2 2 θ 13 6
The Daya Bay Collaboration Europe (2) JINR, Dubna, Russia Charles University, Czech Republic North America (16) Asia (20) BNL, Caltech, Iowa State Univ., Beijing Normal Univ., Illinois Inst. Tech., LBNL, Princeton, Chengdu Univ. of Sci. and Tech., CGNPG, CIAE, RPI, Siena, UC-Berkeley, UCLA, Dongguan Univ.Tech., IHEP, Nanjing Univ., Univ. of Cincinnati, Univ. of Houston, Nankai Univ., NCEPU, Shandong Univ., Univ. of Wisconsin-Madison, Shanghai Jiaotong Univ., Shenzhen Univ., Univ. of Illinois-Urbana-Champaign, Tsinghua Univ., USTC, Zhongshan Univ., Virginia Tech., William & Mary Chinese Univ. of Hong Kong, Univ. of Hong Kong, National Taiwan Univ., National Chiao Tung Univ., National United Univ. ~230 Collaborators � 7
Daya Bay Nuclear Power Complex • ~55 km from Hong Kong central • All 6 reactors are in commercial operation • one of top 5 most powerful nuclear Ling Ao II NPP power plants in the world Ling Ao NPP Daya Bay NPP 6 × 2.95 GW th = 17.7 GW th 8
Production of Reactor ν e • Fission processes in a nuclear core produce radio-nuclides that decay rapidly to yield a huge number of low-energy ν e : 3 GW th generates 6 × 10 20 ν e per sec From L.H. Miller (2000) ν e /MeV/fission Calculated fission rate of a Palo Verde core Resultant ν e spectrum known to 1-2% • ν e related to 235 U, 239 U, and 241 Pu : • Uncertainty in ν e yield, ~2%, due to - measure β spectrum using thermal – Thermal power (<1%) neutron induced fission on the isotope – Sampling of fuel - convert β spectrum to ν e spectrum – Analysis of fractions of • ν e related to 238 U : isotopes in samples - ν e spectrum is based on calculation 9
Detecting Reactor ν e • Use the inverse β -decay reaction in a liquid scintillator: ν e + p → e + + n (prompt signal) ~180 µ s → + p → D + γ (2.2 MeV) (delayed signal) → + Gd → Gd* ~30 µ s → Gd + γ ’s (8 MeV) (delayed signal) for 0.1% Gd γ • Time- and energy-tagged signal is a good tool to suppress background events. ν e γ e + • Energy of ν e is given by: γ E ν ≈ T e+ + T n + (m n - m p ) + m e+ ≈ T e+ + 1.8 MeV 10-40 keV n ν e spectrum γ γ (no oscillation) Arbitrary From Bemporad, Gratta and Vogel 10
Determining θ 13 With Reactor ν e • Look for disappearance of electron antineutrinos from reactors: 2 L 2 L ' * ' * e → x ) ≈ sin 2 2 θ 13 sin 2 Δ m 31 , + cos 4 θ 13 sin 2 2 θ 12 sin 2 Δ m 21 P ( ν ) ) , 4 E 4 E ( + ( + Small-amplitude oscillation Large-amplitude due to θ 13 integrated over E oscillation due to θ 12 Disappearance probability ! • Perform a relative measurement, for a given E : 2 ! $ ! $ ! $ ! $ R Far = L Near N Far & 1 − P & ε Far sin 2 2 θ 13 = 0.1 Far # & # # # & R Near L Far N Near 1 − P ε Near " % " % " % " % Near number yield detection far of ν e rate 1/r 2 efficiency sin 2 2 θ 13 . detector protons near All correlated errors cancelled. detector 11
Far Hall (EH3) Tunnel Ling Ao near Surface Hall (EH2) Assembly Control Building Building (SAB) Ling Ao II Water reactors Hall Construction tunnel Ling Ao reactors LS Hall Daya Bay Near Entrance Hall (EH1) Daya Bay m ! reactors 12
Baselines Detailed Survey: - GPS above ground - Total Station underground - Final precision: 28mm Validation: - 3 independent calculations - Cross-check survey - Consistent with power plant and design plans 13
Daya Bay Detector Design Calibration units Stainless steel (LED, 68 Ge, tank AmC-Co) 4m acrylic tank sandwiched between top and bottom reflectors 20t Gd-LS Four layers of RPC’s 5m (target) to tag muons 20t liquid scint. (gamma catcher) 37t mineral oil shield Inner Cherenkov 192 PMTs 3m acrylic vessel 5m > 2.5m water: Outer Cherenkov - attenuates gamma rays & neutrons - forms two optically decoupled Cherenkov counters 14
Calibration System of Antineutrino Detectors � 3 Automatic calibration ‘robots’ (ACUs) on each detector ACU-C ACU-A ACU-B R=1.7725 m R=0 R=1.35m 3 sources for each z axis on a turntable (position accuracy < 5 mm): 68 Ge (2 × 0.511 MeV γ ’s; 10 Hz ) • 241 Am- 13 C neutron source (3.5 • MeV n without γ ; 0.5 Hz ) 60 Co (1.173+1.332 MeV γ ’s; 100 Hz ) Three axes: center, edge of • LED diffuser ball (500 Hz) � target, middle of gamma catcher � 15
Assemble Antineutrino Detectors Stainless Steel Vessel Install top reflector (SSV) in assembly pit Close SSV Install lower reflector lid Install PMT ladders Install Acrylic Vessels Install calibration units 16
Liquid Scintillators Gd (0.1%) + PPO (3 g/L) + • bis-MSB (15 mg/L) + LAB 185-ton Gd-LS + 196-ton LS • production Number of protons: • (7.169±0.034) × 10 25 p per kg @ 430 nm 185-t 0.1% Gd-LS stored in five 40-t tanks A 1-m apparatus yielded attenuation length of ~15 m @ 430 nm. 17
Fill Antineutrino Detectors (ADs) Move AD into tunnel Fill ADs with Coriolis liquids mass flow underground meters ISO tank • Target mass is measured with: (1) 4 load cells supporting the 20-t ISO tank (2) Coriolis mass flow meters � ���� Absolute uncertainty: 0.02% Relative uncertainty: 0.02% • Temperature is maintained constant • Filling is monitored with in-situ sensors 18
Daya Bay Near Hall (EH1) Install filled AD in pool Fill pool with purified water Data taking started on 15 Aug 2011 Roll RPC over cover Place cover over pool Kam-Biu Luk LP2011 19
Getting Ling Ao Near and Far Halls Ready EH 2 (Ling Ao Near Hall): Began operation on 5 Nov 2011 EH 3 (Far Hall): Started data-taking on 24 Dec 2011 20
Data Taking A. Comparison of two ADs : - 23 Sept. 2011 – 23 Dec. 2011 A - Side-by-side comparison of 2 detectors - Demonstrated detector systematics Hall 1 better than requirements. - Nucl. Instru. Meth. A685, 78 (2012) B. First results on oscillation: - 24 Dec. 2011 – 17 Feb. 2012 B - All 3 halls with 6 ADs operating Hall 2 - Observation of ν e disappearance - Phys. Rev. Lett. 108 (2012) 171803. C. This updated analysis: - 24 Dec. 2011 – 11 May 2012 C - 2.5 times more data collected with the same configuration Hall 3 21
Triggers & Their Performance Discriminator threshold: - ~0.25 p.e . for PMT signal NHit Triggers: - AD: ≥ 45 PMTs (digital trigger) ≥ 0.4 MeV (analog trigger) - Inner Water Cherenkov: ≥ 6 PMTs - Outer Water Cherenkov: ≥ 7 PMTs (near) ≥ 8 PMTs (far) - RPC: 3/4 layers in each module ESum Trigger rate: - AD: < 280 Hz - Inner Water Cherenkov: < 160 Hz - Outer Water Cherenkov: < 200 Hz 22
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