Daya Bay and Other Reactor Neutrino Oscillation Experiments Jen-Chieh Peng University of Illinois at Urbana-Champaign International Workshop on “High Energy Physics in the LHC Era” Valparaiso, Chile, December 11-15, 2006

Outline

What we have learned from neutrino oscillation experiments

What we do not know about the neutrinos Dirac or Majorana neutrinos? Mass hierachy and values of the masses? Existence of sterile neutrinos? Value of the θ13 mixing angle? Values of CP-violation phases? Origins of the neutrino masses? Other unknown unknowns …..

What we know and do not know about the neutrinos What is the νe fraction of ν3? (proportional to sin2θ13) Contributions from the CP-phase δ to the flavor compositions of neutrino mass eigenstates depend on sin2θ13)

Why measuring θ13? A recent tabulation of predictions of 63 neutrino mass models on sin2θ13 (hep-ph/0608137) Models based on the Grand Unified Theories in general give relatively large θ13 Models based on leptonic symmetries predict small θ13 A measurement of sin22θ13 at the sensitivity level of 0.01 can rule out at least half of the models!

Why measuring θ13? A recent tabulation of predictions of 63 neutrino mass models on sin2θ13 (hep-ph/0608137) A measurement of sin22θ13 AND the mass hierarchy can rule out even more models!

Why measuring θ13? Leptonic CP violation If sin22θ13>0.02-0.03, then NOvA+T2K will have good coverage on CP δ. Reactor experiments sets the scale for future studies

Current Knowledge of 13 Global fit Direct search allowed region sin2213 < 0.11 (90% CL) Best fit value of m232 = 2.4  103 eV2 sin2213 = 0.04 At m231 = 2.5  103 eV2, sin22 < 0.17 allowed region Fogli etal., hep-ph/0506083

Some Methods For Determining 13 Method 1: Accelerator Experiments decay pipe horn absorber target p detector + +   e appearance experiment need other mixing parameters to extract 13 baseline O(100-1000 km), matter effects present expensive Method 2: Reactor Experiments e  X disappearance experiment baseline O(1 km), no matter effect, no ambiguity • relatively cheap

Discovery of the Neutrino – 1956 F. Reines, Nobel Lecture, 1995

Detecting : Inverse  Decay The reaction is the inverse -decay in 0.1% Gd-doped liquid scintillator: e  p  e+ + n (prompt)  + p  D + (2.2 MeV) (delayed) + Gd  Gd*  Gd + ’s(8 MeV) (delayed) 0.3b 50,000b Arbitrary Flux Cross Section Observable n Spectrum From Bemporad, Gratta and Vogel 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+ + 1.8 MeV 10-40 keV

Measuring 13 with Reactor Neutrinos Search for 13 in new oscillation experiment Small-amplitude oscillation due to 13 integrated over E Large-amplitude oscillation due to 12 13 m213≈ m223 Reactor theta13 is an LDRD activity here at Berkeley, Daya Bay has emerged as one of leading contenders in worldwide effort to mount next-generation reactor neutrino experiment. ~1-1.8 km detector 1 detector 2 > 0.1 km

Results from Chooz Systematic uncertainties P = 8.4 GWth L = 1.05 km 5-ton 0.1% Gd-loaded liquid scintillator to detect e + p  e+ + n L = 1.05 km D = 300 mwe P = 8.4 GWth ~3000 e candidates (included 10% bkg) in 335 days Systematic uncertainties Rate: ~5 evts/day/ton (full power) including 0.2-0.4 bkg/day/ton

How to Reach a Precision of 0.01 in sin2213? Increase statistics: Use more powerful nuclear reactors Utilize larger target mass, hence larger detectors Suppress background: Go deeper underground to gain overburden for reducing cosmogenic background Reduce systematic uncertainties: Reactor-related: Optimize baseline for best sensitivity and smaller reactor-related 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)

World of Proposed Reactor Neutrino Experiments Chooz, France Krasnoyasrk, Russia Braidwood, USA Kashiwazaki, Japan RENO, Korea Diablo Canyon, USA Daya Bay, China Angra, Brazil

Reactor 13 Experiment at Krasnoyarsk, Russia Original ideal, first proposed at Neutrino2000 Krasnoyarsk - underground reactor - detector locations determined by infrastructure ~20000 ev/year ~1.5 x 106 ev/year Reactor Ref: Marteyamov et al, hep-ex/0211070

KASKA at Kashiwazaki, Japan Kashiwazaki-Kariwa Nuclear Power Station - 7 nuclear power stations, World’s most powerful reactors - requires construction of underground shaft for detectors near far 70 m 200-300 m 6 m shaft hole, 200-300 m depth sin2(213) < 0.02 http://kaska.hep.sc.niigata-u.ac.jp/ See poster by F. Suekane

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, 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. ~ 125 collaborators

Location of Daya Bay 45 km from Shenzhen 55 km from Hong Kong

The Daya Bay Nuclear Power Complex 12th most powerful in the world (11.6 GWth) Fifth most powerful by 2011 (17.4 GWth) Adjacent to mountain, easy to construct tunnels to reach underground labs with sufficient overburden to suppress cosmic rays 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 Daya Bay NPP: 2  2.9 GWth

Total length: ~3100 m Far site 1615 m from Ling Ao 1985 m from Daya Overburden: 350 m Empty detectors: moved to underground halls through access tunnel. Filled detectors: transported between underground halls via horizontal tunnels. 900 m Ling Ao Near ~500 m from Ling Ao Overburden: 112 m Mid site 873 m from Ling Ao 1156 m from Daya Overburden: 208 m Ling Ao-ll NPP (under const.) 465 m 810 m Construction tunnel Ling Ao NPP Filling hall entrance 295 m Daya Bay Near 363 m from Daya Bay Overburden: 98 m Daya Bay NPP Total length: ~3100 m

Conceptual design of the tunnel and the Site investigation including bore holes completed

Tunnel construction The tunnel length is about 3000m Local railway construction company has a lot of experience (similar cross section) Cost estimate by professionals, ~ 3K $/m Construction time is ~ 15-24 months A similar tunnel on site as a reference

Antineutrino Detectors Three-zone cylindrical detector design Target zone, gamma catcher zone (liquid scintillator), buffer zone (mineral oil) Gamma catcher detects gamma rays that leak out 0.1% Gd-loaded liquid scintillator as target material Short capture time and high released energy from capture, good for suppressing background Eight ‘identical’ detector modules, each with 20 ton target mass ‘Identical’ modules help to reduce detector-related systematic uncertainties Modules can cross check the performance of each other when they are brought to the same location 20 ton 0.1% Gd-LS  catcher buffer

Event Rates per Detector Module Source Units DB LA far Use Antineutrino Signal (day-1) 930 760 90 signal Radioactive Backgrounds (Hz) 30 e+-thresh. Rock 4 PMT glass 8 other materials (steel) 18 Gd contamination 1 Muons 24 14 Single neutron 9000 6000 400 cal. Tagged single neutron 480 320 45 cal./bkg. Tagged fast neutron 20 13 2 Bkg est b emitters (6-10 MeV) 210 140 15 n-thresh. 12B 270 28 8He+9Li 3 Bkg

Key Requirements for Gd-LS for Daya Bay High light transmission = high optical attenuation length (low optical absorbance). High light output in the Liquid Scintillator, LS. Long-term chemical stability, since the experiment will go on for at least 3 years. Stability of the LS means no development of color; no colloids, particulates, cloudiness, nor precipitation; no gel formation; no changes in optical properties.

BNL Gd-LS Optical Attenuation: Stable So Far ~700 days Gd-carboxylate in PC-based LS stable for ~2 years. - Attenuation Length >15m (for abs < 0.003). Promising data for Linear Alkyl Benzene, LAB (LAB use suggested by SNO+ experiment).

Detector Prototype at IHEP 0.5 ton prototype (currently unloaded liquid scintillator) 45 8” EMI 9350 PMTs: 14% effective photocathode coverage with top/bottom reflectors ~240 photoelectron per MeV : 9%/E(MeV) prototype detector at IHEP Put in difference plot Energy Resolution

Background Sources 1. Natural Radioactivity: PMT glass, steel, rock, radon in the air, etc 2. Slow and fast neutrons produced in rock & shield by cosmic muons 3. Muon-induced cosmogenic isotopes: 8He/9Li which can -n decay - Cross section measured at CERN (Hagner et. al.) - Can be measured in-situ, even for near detectors with muon rate ~ 10 Hz

Cosmic-ray Muon Use a modified Geiser parametrization for cosmic-ray flux at surface Apply MUSIC and mountain profile to estimate muon intensity & energy 355 m 98 m 112 m 208 m Daya Bay Ling Ao Far Mid DYB LingAo Mid Far Overburden (m) 98 112 208 355 Muon intensity (Hz/m2) 1.16 0.73 0.17 0.041 Mean Energy (GeV) 55 60 97 138

(Water buffer + water cherenkov + RPC tracker) Muon Veto System (Water buffer + water cherenkov + RPC tracker) Water shield also serves as a Cherenkov counter for tagging muons Water Cherenkov modules along the walls and floor Augmented with a muon tracker: RPCs Combined efficiency of Cherenkov and tracker > 99.5% with error measured to better than 0.25%

Summary of Systematic Uncertainties sources Uncertainty Reactors 0.087% (4 cores) 0.13% (6 cores) Detector (per module) 0.38% (baseline) 0.18% (goal) Backgrounds 0.32% (Daya Bay near) 0.22% (Ling Ao near) 0.22% (far) Signal statistics 0.2%

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: China atomic energy agency China nuclear safety agency Supported by BNL/LBNL seed funds Supported by DOE $800K R&D fund Support by funding agencies from other countries & regions China plans to provide civil construction and ~half of the detector systems; U.S.plans to bear ~half of the detector cost IHEP & CGNPG IHEP & LBNL

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

Sensitivity to Sin22q13 Other physics capabilities: Supernova watch, Sterile neutrinos, …

Double Chooz 0.1-0.2 km 1.05 km Sensitivity 10 tons detectors 8.4 GWth reactor power 300 mwe overburden at far site 60 mwe overburden at near site 0.1-0.2 km 1.05 km Sensitivity sin2(213) < 0.03 at 90% CL after 3 yrs, matm2 = 2 x 10-3 eV2 http://doublechooz.in2p3.fr/

Reactor Experiment for Neutrino Oscillations (RENO) at YongGwang, Korea 20tons (fid. vol.) of liquid scintillator detectors 3 nearest detectors of 200~300kg scintillators Begin of data taking 2009/2010 sin2(213) < 0.02 (88m high) (260m high) Near Detector Tunnel length: ~100m Far Detector Tunnel length: ~600m 150m ~1.5 km

Prospects for a Reactor Measurement of sin2213 Angra, Brazil sin2213 < 0.005 R&D on reactor monitoring. Proposal for 13 measurement after Double Chooz. Daya Bay, China sin2213 < 0.01 Approved by the Chinese Academy of Science for 50M RMB. Other Chinese agencies are expected to contribute ~100M RMB. US DOE has provided 0.8M$ for R&D for FY06. Working towards US project start in FY08. Plan to start near-mid data taking in 2009, and begin full operation in 2010. Double-CHOOZ, France sin2213 < 0.03 Funding committment in France and Germany. Begin running far detector in 2008. Complete near detector in 2009. RENO, Korea sin2213 < 0.02 Approved by Ministry of Science and Technology for US $9M. R&D program starting. Plan to begin data taking in 2009/2010.

Neutrino Physics at Reactors Past Experiments Hanford Savannah River ILL, France Bugey, France Rovno, Russia Goesgen, Switzerland Krasnoyark, Russia Palo Verde Chooz, France Reactors in Japan 1956 First observation of neutrinos 1980s & 1990s Reactor neutrino flux measurements in U.S. and Europe 1995 Nobel Prize to Fred Reines at UC Irvine 2002 Discovery of reactor antineutrino oscillation 2006 and beyond Precision measurement of 13 Exploring feasibility of CP violation studies

S. Glashow