Daya Bay Reactor Neutrino Experiment A Project for
Daya Bay Reactor Neutrino Experiment --- A Project for Precise Measurement of 13 Changgen Yang Institute of High Energy Physics, Beijing for the Daya Bay Collaboration 2 nd Sino-French Workshop on the Dark Universe November 13, 2006 1
Outline • Physics Motivation • Requirements • The Daya Bay Experiment – – Layout Detector (AD and Muon system) Design Backgrounds Systematic Errors and Sensitivity • Site Survey, Design and R&D • Schedule and Funding • Summary 2
13 The Last Unknown Neutrino Mixing Angle UMNSP Matrix ? atmospheric, K 2 K reactor and accelerator 23 = ~ 45° 13 = ? SNO, solar SK, Kam. LAND 12 ~ 32° 0 ? • What is e fraction of 3? • Ue 3 is a gateway to CP violation in neutrino sector: P( e) - P( e) sin(2 12)sin(2 23)cos 2( 13)sin(2 13)sin 3
Current Knowledge of 13 Direct search Global fit Sin 2(2 13) < 0. 09 At m 231 = 2. 5 10 3 e. V 2, sin 22 < 0. 15 Sin 22 13 < 0. 18 allowed region Best fit value of m 232 = 2. 4 10 3 e. V 2 Fogli etal. , hep-ph/0506083 4
Measuring sin 22 13 at reactors • • Clean signal, no cross talk with d and matter effects Relatively cheap compared to accelerator based experiments Provides the direction to the future of neutrino physics Rapid deployment possible Reactor exp. Pee sin 22 13 sin 2 (1. 27 Dm 213 L/E) cos 4 13 sin 22 12 sin 2 (1. 27 Dm 212 L/E) Long baseline accelerator exp. Pme ≈ sin 2 23 sin 22 13 sin 2(1. 27 Dm 223 L/E) + cos 2 23 sin 22 12 sin 2(1. 27 Dm 212 L/E) A(r) cos 2 13 sin 13 sin(d) 5
Daya Bay: Goals And Approach • Utilize the Daya Bay nuclear power facilities to: - determine sin 22 13 with a sensitivity of 1% - measure m 231 • Adopt horizontal-access-tunnel scheme: - mature and relatively inexpensive technology - flexible in choosing overburden and changing baseline - relatively easy and cheap to add experimental halls - easy access to underground experimental facilities - easy to move detectors between different locations with good environmental control. • Employ three-zone antineutrino detectors. 6
How to reach 1% precision ? • Increase statistics: – Powerful nuclear reactors(1 GWth: 6 x 1020 e/s) – Larger target mass • Reduce systematic uncertainties: – Reactor-related: • Optimize baseline for best sensitivity and smaller residual errors • Near and far detectors to minimize reactor-related errors – Detector-related: • Use “Identical” pairs of detectors to do relative measurement • Comprehensive program in calibration/monitoring of detectors • Interchange near and far detectors (optional) – Background-related • Go deep to reduce cosmic-induced backgrounds • Enough active and passive shielding 7
The Daya Bay Nuclear Power Facilities 45 km 55 km Ling Ao II NPP: 2 2. 9 GWth Ready by 2010 -2011 Ling Ao NPP: 2 2. 9 GWth 1 GWth generates 2 × 1020 e per sec • 12 th most powerful in the world (11. 6 GW) • Top five most powerful by 2011 (17. 4 GW) • Adjacent to mountain, easy to construct tunnels to reach underground labs with sufficient overburden to suppress cosmic rays Daya Bay NPP: 2 2. 9 GWth 8
Where To Place The Detectors ? • Since reactor e are low-energy, it is a disappearance experiment: Small-amplitude oscillation due to 13 integrated over E • Place near detector(s) close to reactor(s) to 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, and also be less affected by 12 Large-amplitude oscillation due to 12 Sin 22 = 0. 1 m 231 = 2. 5 x 10 -3 e. V 2 Sin 22 2 = 0. 825 m 221 = 8. 2 x 10 -5 e. V 2 far detector near detector 9
Baseline optimization and site selection • • Neutrino flux and spectrum Detector systematical error Backgrounds from environment Cosmic-ray induced backgrounds (rate and shape) taking into mountain shape: fast neutrons, 9 Li, … 10
Baseline optimization and site selection Far site 1600 m from Ling Ao 2000 m from Daya Overburden: 350 m m 0 1 9 Empty detectors: moved to underground halls through access tunnel. Filled detectors: swapped between underground halls via horizontal tunnels. Ling Ao Near 500 m from Ling Ao Overburden: 98 m 290 m (8% slope) Entrance portal 730 m Mid site ~1000 m from Daya Overburden: 208 m 570 Ling Ao-ll NPP (under const. ) m 230 m (15% slope) Ling Ao NPP Daya Bay Near 360 m from Daya Bay Overburden: 97 m Daya Bay NPP Total length: ~2700 m 11
A Versatile Site • Rapid deployment: - Daya Bay near site + mid site - 0. 7% reactor systematic error • Full operation: (A) Two near sites + Far site (B) Mid site + Far site (C) Two near sites + Mid site + Far site Internal checks, each with different systematic 12
Baseline detector design: multiple neutrino modules and multiple vetos • Multiple anti-neutrino detector modules for side -by-side cross check • Multiple muon tagging detectors: – Water pool as Cherenkov counter – Water modules along the walls and floor as muon tracker – RPC at the top as muon tracker – Combined efficiency > (99. 5 0. 25) % Redundancy is a key for the success of this experiment 13
Alternative detector Design: Aquarium Tunnel • Dry detectors • Easier to deploy detectors • Can access detectors • Radon from rock can easily diffuse into detectors during data taking • Less temperature regulation 14
Detecting Low-energy e • The reaction is the inverse -decay in 0. 1% Gd-doped liquid scintillator: e p e+ + n (prompt) 0. 3 b Arbitrary 50, 000 b + p D + (2. 2 Me. V) (delayed) + Gd Gd* Gd + ’s(8 Me. V) (delayed) From Bemporad, Gratta and Vogel Observable Spectrum 10 -40 ke. V n e o cti Flu x Cr o S ss • Time- and energy-tagged signal is a good tool to suppress background events. • Energy of e is given by: E Te+ + Tn + (mn - mp) + m e+ Te+ + 1. 815 Me. V
What Target Mass Should Be? (3 year run) DYB: B/S = 0. 5% LA: B/S = 0. 4% Far: B/S = 0. 1% m 231 = 2 10 -3 e. V 2 Systematic error Black : 0. 6% Red : 0. 25% (baseline goal) Blue : 0. 12% tonnes 16
Design of Antineutrino Detectors • • Three-zone structure: I. Target: 0. 1% Gd-loaded liquid scintillator II. Gamma catcher: liquid scintillator, 45 cm III. Buffer shielding: mineral oil, ~45 cm 20 tonns Gd-LS Possibly with diffuse reflection at ends. ~200 PMT’s around the barrel: oil buffer gamma catcher Oil buffer thickness Isotopes (from PMT) Purity (ppb) 20 cm 25 cm 30 cm 40 cm (Hz) 238 U(>1 Me. V) 50 2. 7 2. 0 1. 4 0. 8 232 Th(>1 Me. V) 50 1. 2 0. 9 0. 7 0. 4 40 K(>1 Me. V) 10 1. 8 1. 3 0. 9 0. 5 5. 7 4. 2 3. 0 Total 17 1. 7
Why three zones ? Chooz • 3 zones provides increased confidence in systematic error associated with detection efficiency and fiducial volume • 2 zones implies simpler design/construction, some cost reduction but with increased risk to systematic error n capture on Gd yields 8 Me. V with 3 -4 3 -ZONE background ’s 2 -ZONE 18
Central Detector modules • Three zones modular structure: I. target: Gd-loaded scintillator II. g-catcher: normal scintillator III. Buffer shielding: oil 20 t Gd-LS • Reflector at top and bottom • 224 8”PMT/module • Photocathode coverage: 5. 6 % 12%(with reflector) s. E/E = 12%/ E LS oil sr = 13 cm Target: 20 t, 1. 6 m g-catcher: 20 t, 45 cm Buffer: 40 t, 45 cm 19
Gd-loaded Liquid Scintillator For Daya Bay • Require stable Gd-loaded liquid scintillator with - high light yield - long attenuation length • BNL/IHEP/JINR nuclear chemists study on metal-loaded liquid scintillator for Daya Bay: - Gd-carboxylate in PC-based LS stable for ~2 years. - Attenuation Length >15 m (for abs < 0. 003). - Promising data for Linear Alkyl Benzene, LAB (LAB use suggested by 20 SNO+ experiment).
Calibration and Monitoring • Source calibration: energy scale, resolutions, … – Deployment system • Automatic: quick but limited space points • Manual: slow but everywhere – Choices of sources: energy(0. 5 -8 Me. V), activity(<1 KHz), g/n, … • Calibration with physics events: – Neutron capture – Cosmic-rays • • LED calibration: PMT gain, liquid transparency, … Environmental monitoring: temp. , voltage, radon, … Mass calibration and high precision flow meters Material certification 21
Muon System • To shield the antineutrino detectors from natural and cosmogenic background and serve as an active muon detector. – Attenuate rock radioactivity, fast neutrons from walls, etc. • To register the presence of a cosmic ray muon and measure its time and position with respect to candidate events – To allow measurement (& subtraction) of backgrounds from cosmogenic isotopes – To reject fast neutron background from muon interactions in the water (activity in the antineutrino detectors w/i 200 s of a muon will be ignored) – To study and reduce fast neutron background from muon interactions in the rock • For the water pool option, the water also regulates the temperature of the antineutrino detectors 22
Muon System (Water Buffer & Veto) • 2. 5 m water buffer to shield backgrounds from neutrons and g’s from lab walls • Cosmic-muon VETO requirement: – Inefficiency < 0. 5% – known to <0. 25% • Solution: multiple detectors • Multiple detectors: can also cross check each other to control uncertainties Neutron background vs water shielding thickness 2. 5 m water 23
Backgrounds • 9 Li/8 He (correlated background) – -n cascade, Prompt: , Delayed: n • “Fast neutron” backgrounds (correlated background) – Energetic neutrons produced by muon, Prompt: recoil proton, Delayed: thermalized neutron • Accidental backgrounds (uncorrelated background) – Positron-like signal (Singles, <100 Hz) • Natural radioactivity (PMT, Rock, Steel Vessel, LS, … <50 Hz) • Muon, cosmogenic isotopes, etc – Neutron-like signal (<200/day) • Single neutrons: Muon neutron single neutron in detector • Long lived isotopes (e. g. 12 B/12 N) • Other events in 6 -10 Me. V Background Sources: cosmic muons and radioactivity 24
Muon Simulation Detailed topographic map, modified Gaisser formula, and MUSIC to transport muons. 25
Neutron Simulation n n • Muons from MUSIC simulation. • Geant 3 + GCALOR for neutron transportation • Neutrons produced by muons in rock, water, and mineral oil along the muon track • Neutron yield, energy spectrum, and angular distribution. Accurate to ~20% Y. Wang et al. , PRD 64, 013012(2001) • Quenching on recoil proton is important • No optical simulation Neutron multiplicity at production At the far site, 1 neutron/3. 4 muons 26
In-situ 9 Li measurement • Log likelihood fitting 9 Li neutrino 3 years’ data 0. 36% error at DYB site 0. 27% at LA near site 0. 10% at the far site The unknown is 9 Li cross section. Combine DYB and LA site 9 Li/Signal can be measured in-situ to 0. 2% at the near sites with 3 years’ data. Independent of background level. Verified by Monte Carlo u. L. J. Wen et. al. NIM A 564 (2006) 471 27
Background related errors • Uncorrelated backgrounds: U/Th/K/Rn/neutron Single gamma rate @ 0. 9 Me. V < 50 Hz Single neutron rate < 1000/day • Correlated backgrounds: n Em 0. 75 Fast Neutrons: double coincidence 8 He/9 Li: neutron emitting decays 28
Summary of Systematic Errors Multiple, identical detectors/site 3 -zone design Overburden/shielding Absolute measurement Relative measurement Baseline: currently achievable relative uncertainty without R&D Goal: expected relative uncertainty after R&D 29
Sensitivity of Daya Bay in sin 22 13 90% confidence level Far hall (80 t) Ling Ao near hall (40 t) Super-K 90% CL ) t 40 id ( +m 0 t) ar r (4 1 ye nea 2 near + far (3 years) Near-mid Use rate and spectral shape Tunnel entrance Daya Bay near hall (40 t) 30
Site Survey and Tunnel Design Geophysical profile (Daya–mid--far) 31
Bore Samples Zk 4 (depth: 133 m) Zk 2 (depth: ~180 m) At tunnel depth Zk 1 (depth: 210 m) Zk 3 (depth: ~64 m) 32
Findings of Geotechnical Survey • No active or large fault • Earthquake is infrequent • Rock structure: massive and blocky granite • Rock mass: most is slightly weathered or fresh • Groundwater: low flow at the depth of the tunnel • Quality of rock mass: stable and hard Good geotechnical conditions for tunnel construction 33
Tunnel construction • The tunnel length is about 3000 m • Local railway construction company has a lot of experience (similar cross section) • Cost estimate by professionals, ~ 3 K $/m • Construction time is ~ 18 -24 months • A similar tunnel on site as a reference 34
Gas room Water Purif. Counting room Experimental Hall (Conceptual Design) 35
Prototype setup at IHEP Flange to put Source Purposes: Test reflection, energy resolution, LS performance … Cables LED • Inner acrylic vessel: 1 m in diameter and 1 m tall, filled with normal liquid scintillator(70% mineral oil + 30% mesitylene). • Outer stainless steel vessel: 2 m in diameter and 2 m tall, filled with mineral oil. PMTs mounted and immerged in oil. • 45 MACRO PMT, 15 PMT/Ring 36
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137 Cs 0. 662 Me. V gamma, 164 p. e. ; Energy resolution 10%. im l e i y Co 2. 506 Me. V gamma, 666 p. e. ; r na Energy resolution 5. 6%. 60 r P 38
Schedule • begin civil construction April 2007 • Bring up the first pair of detectors Jun 2009 • Begin data taking with the Near-Mid configuration Sept 2009 • Begin data taking with the Near-Far configuration Jun 2010 39
Funding and other supports • Funding Committed from • Chinese Academy of Sciences, • Ministry of Science and Technology • Natural Science Foundation of China • China Guangdong Nuclear Power Group • Shenzhen municipal government • Guangdong provincial government • Gained strong support from: IHEP & CGNPG • China Guangdong Nuclear Power Group • China atomic energy agency • China nuclear safety agency • Supported by BNL/LBNL seed funds • Supported by DOE $800 K R&D fund • Support by funding agencies from other IHEP & LBNL countries & regions • China plans to provide civil construction and ~half of the detector systems; U. S. plans to bear ~half of the detector cost 40
Summary • 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 22 13. • The Daya Bay Collaboration continues to grow. • Design of detectors is in progress and R&D is ongoing. Detailed engineering design of tunnels and infrastructures will begin soon • Plan to start civil construction in 2007, deploying detectors in 2009, and begin full operation in 2010 41
Daya Bay collaboration Europe (3) (9) JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic North America (13)(46) BNL, Caltech, LBNL, Iowa state Univ. Illinois Inst. Tech. , Princeton, RPI, UC-Berkeley, UCLA, Univ. of Houston, Univ. of Wisconsin, Virginia Tech. , Univ. of Illinois-Urbana-Champaign, ~ 125 collaborators Asia (13) (70) IHEP, CIAE, Tsinghua Univ. Zhongshan Univ. , Nankai Univ. Beijing Normal Univ. , Nanjing Univ. Shenzhen Univ. , Hong Kong Univ. Chinese Hong Kong Univ. Taiwan Univ. , Chiao Tung Univ. , National United Univ. 42
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