Measuring sin 2 2  13 with the Daya Bay nuclear power reactors Yifang Wang Institute of High Energy Physics

Neutrinos Basic building blocks of matter ： Tiny mass, neutral, almost no interaction with matter, very difficult to detect. Enormous amount in the universe, ~ 100/cm 3, about 0.3% -1% of the total mass of the universe Most of particle and nuclear reactions produce neutrinos: particle and nuclear decays, fission reactors, fusion sun, supernova,  -burst ， cosmic-rays …… Important in the weak interactions ： P violation from left-handed neutrinos Important to the formation of the large structure of the universe, may explain why there is no anti-matter in the universe

Brief history of neutrinos 1930 Pauli postulated neutrinos 1956 Neutrinos discovered （ 1995 Nobel prize ） 1962 μ-neutrino discovered （ 1988 Nobel prize ） 1957 Pontecorvo proposed neutrino oscillation 1968 solar neutrino deficit, oscillation ? （ 2002 Nobel prize ） 1998 atmospheric neutrino anomaly => oscillation (2002 Nobel prize ） 2001 SNO:solar e conversion => oscillation 2002 KamLAND:reactor e deficit => oscillation Neutrino oscillation: a way to detect neutrino mass A new window for particle physics, astrophysics, and cosmology

Neutrino oscillation: PMNS matrix EXO Genius CUORE NEMO A total of 6 parameters: 2  m 2, 3 angles, 1 phases + 2 Majorana phases If Mass eigenstates  Weak eigenstates  Neutrino oscillation Oscillation probability ： P  sin 2 (1.27  m 2 L/E) Atmospheric solar  decays crossing ： CP 与  13 Super-K K2K Minos T2K Daya Bay Double Chooz NOVA Homestake Gallex SNO KamLAND

Evidence of Neutrino Oscillations Unconfirmed: LSND:  m 2 ~ eV 2 Confirmed: Atmospheric:  m 2 ~ 2  eV 2 Solar:  m 2 ~ 8  eV 2 P      sin 2 2  sin 2 (1.27  m 2 L/E) 2 flavor oscillation in vacuum:

A total of six mixing parameters ： Known ： |  m 2 32 |, sin 2 2  32 --Super-K  m 2 21, sin 2 2  21 --SNO,KamLAND Unknown ： sin 2 2   ，  , sign of  m 2 32 at reactors: P ee  1  sin 2 2   sin 2 (1.27  m 2  L/E)  cos 4   sin 2 2   sin 2 (1.27  m 2  L/E) at LBL accelerators: P  e ≈ sin 2   sin 2 2   sin 2 (1.27  m 2  L/E) + cos 2   sin 2 2   sin 2 (1.27  m 2 12 L/E)  A(  )  cos 2  13 sin    sin(  )

Why at reactors Clean signal, no cross talk with  and matter effects Relatively cheap compare to accelerator based experiments Can be very quick Provides the direction to the future of neutrino physics Small-amplitude oscillation due to  13 Large-amplitude oscillation due to  12

Current Knowledge of  13 Global fit fogli etal., hep-ph/ Sin 2 (2  13 ) < 0.09 Sin 2 (2  13 ) < 0.18 Direct search PRD 62, Allowed region

No good reason(symmetry) for sin 2 2  13 =0 Even if sin 2 2  13 =0 at tree level, sin 2 2  13 will not vanish at low energies with radiative corrections Theoretical models predict sin 2 2  13 ~ % An experiment with a precision for sin 2 2  13 less than 1% is desired model prediction of sin 2 2  13 Experimentally allowed at 3  level

Importance to know  13 1 ） A fundamental parameter 2 ） important to understand the relation between leptons and quarks, in order to have a grand unified theory beyond the Standard Model 3 ） important to understand matter-antimatter asymmetry –If sin 2 2    ， next generation LBL experiment for CP –If sin 2 2    next generation LBL experiment for CP ??? 4 ） provide direction to the future of the neutrino physics: super-neutrino beams or neutrino factory ?

Recommendation of APS study report: APS

How to do this experiment

How Neutrinos are produced in reactors ? The most likely fission products have a total of 98 protons and 136 neutrons, hence on average there are 6 n which will decay to 6p, producing 6 neutrinos Neutrino flux of a commercial reactor with 3 GW thermal : 6   s

Fission rate evolution with time in the Reactor Neutrino rate and spectrum depend on the fission isotopes and their fission rate

Neutrino energy spectrum F  exp(a+bE +cE  ) K. Schreckenbach et al., PLB160,325 A.A. Hahn, et al., PLB218,365 P. Vogel et al., PRD39,3378

Reactor thermal power Fission rate depend on the thermal power Typically Known to ~ 1%

Prediction of reactor neutrino spectrum Three ways to obtain reactor neutrino spectrum: –Direct measurement –First principle calculation –Sum up 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%) They all agree well within 3%

10-40 keV Neutrino energy: Neutrino Event: coincidence in time, space and energy neutrino detection: Inverse-β reaction in liquid scintillator 1.8 MeV: Threshold   or  s(0.1% Gd) n + p  d +  (2.2 MeV) n + Gd  Gd* +  (8 MeV)

Reactor Experiment: comparing observed/expected neutrinos: Palo Verde CHOOZ KamLAND Typical precision: 3-6%

How to reach 1% precision ? Three main types of errors: reactor related(~2-3%), background related (~1-2%) and detector related(~1-2%) Use far/near detector to cancel reactor errors Movable detectors, near far, to cancel part of detector systematic errors Optimize baseline to have best sensitivity and reduce reactor related errors Sufficient shielding to reduce backgrounds Comprehensive calibration to reduce detector systematic errors Careful design of the detector to reduce detector systematic errors Large detector to reduce statistical errors

Systematic error comparison Chooz Palo VerdeKamLANDDaya Bay Reactor power <0.1% Reactor fuel/  spectra cross section No. of protonsH/C ratio  0 Mass  0 EfficiencyEnergy cuts Position cuts Time cuts P/Gd ratio n multiplicity0.5- <0.1 backgroundcorrelated uncorrelated <0.1 Trigger02.90 <0.1 livetime

xperi Angra, Brazil Diablo Canyon, USA Braidwood, USA Chooz, France Krasnoyasrk, Russia Kashiwazaki,Japan Daya Bay, China Young Gwang, South Korea Proposed Reactor Neutrino Experiments

Currently Proposed experiments Site (proposal) Power (GW) Baseline Near/Far (m) Detector Near/Far(t) Overburden Near/Far (MWE) Sensitivity (90%CL) Double Chooz (France) /106710/1060/300~ 0.03 Daya Bay (China) /500/180040/40/80260/260/910~ Kaska (Japan) /1600 6/6/2  6 90/90/260~ 0.02 Reno (S. Korea) /150020/20230/675~ 0.03

Daya Bay nuclear power plant 4 reactor cores, 11.6 GW 2 more cores in 2011, 5.8 GW Mountains near by, easy to construct a lab with enough overburden to shield cosmic-ray backgrounds

Convenient Transportation, Living conditions, communications DYB NPP region - Location and surrounding 60 km

Cosmic-muons at sea level: modified Gaisser formula

Cosmic-muons at the laboratory

Baseline optimization and site selection Neutrino spectrum and their error Neutrino statistical error Reactor residual error Estimated detector systematical error: total, bin-to-bin Cosmic-rays induced background (rate and shape) taking into mountain shape: fast neutrons, 9Li, … Backgrounds from rocks and PMT glass

Best location for far detectors Rate only Rate + shape

Total Tunnel length 3200 m Detector swapping in a horizontal tunnel cancels most detector systematic error. Residual error ~0.2% Backgrounds B/S of DYB,LA ~0.5% B/S of Far ~0.2% Fast Measurement DYB+Mid, Sensitivity (1 year) ~0.03 Full Measurement DYB+LA+Far, from 2010 Sensitivity (3 year) <0.01 The Layout LA: 40 ton Baseline: 500m Overburden: 98m Muon rate: 0.9Hz/m 2 Far: 80 ton 1600m to LA, 1900m to DYB Overburden: 350m Muon rate: 0.04Hz/m 2 DYB: 40 ton Baseline: 360m Overburden: 97m Muon rate: 1.2Hz/m 2 Access portal Waste transport portal 8% slope 0% slope Mid: Baseline: ~1000m Overburden: 208m

Geologic survey completed, including boreholes Weathering bursa ( 风化囊） Faults( small ) far near mid

Site investigation completed

Engineering Geological Map

Engineering geological sections Line A

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 ~ months A similar tunnel on site as a reference

How large the detector should be ?

Detector: Multiple modules Multiple modules for cross check, reduce uncorrelated errors Small modules for easy construction, moving, handing, … Small modules for less sensitive to scintillator aging Scalable Two modules at near sites Four modules at far site: Side-by-side cross checks

Central Detector modules Three zones modular structure: I. target: Gd-loaded scintillator  -ray catcher: normal scintillator III. Buffer shielding: oil Reflection at two ends 20t target mass, ~200 8”PMT/module  E =  s ~ 14 cm I II III IsotopesPurity (ppb) 20cm (Hz) 25cm (Hz) 30cm (Hz) 40cm (Hz) 238 U(>1MeV) Th(>1MeV) K(>1MeV) Total  Catcher thickness Oil buffer thickness

Water Buffer & VETO 2m water buffer to shield backgrounds from neutrons and  ’s from lab walls Cosmic-muon VETO Requirement: –Inefficiency < 0.5% –known to <0.25% Solution: Two active vetos –active water buffer, Eff.>95% –Muon tracker, Eff. > 90% RPC scintillator strips –total ineff. = 10%*5% = 0.5% Neutron background vs water shielding thickness 2m water

Two tracker options : –RPC outside the steel cylinder –Scintillator Strips sink into the water RPC from IHEP Scintillator Strips from Ukraine Contribution of JINR,Dubna

Background related error Need enough shielding and an active veto How much is enough ?  error < 0.2% –Uncorrelated backgrounds: U/ Th /K/Rn/neutron single gamma 0.9MeV < 50Hz single neutron rate < 1000/day 2m water + 50 cm oil shielding –Correlated backgrounds: n  E  0.75 Neutrons: >100 MWE + 2m water Y.F. Wang et al., PRD64(2001) He/ 9 Li: > 250 MWE(near) & >1000 MWE(far) T. Hagner et al., Astroparticle. Phys. 14(2000) 33

Fast neutron spectrum Precision to determine the 9 Li background in situ Spectrum of accidental background

Background estimated by GEANT MC simulation Nearfar Neutrino signal rate(1/day)56080 Natural backgrounds(Hz)45.3 Single neutron(1/day)242 Accidental BK/signal0.04%0.02% Correlated fast neutron Bk/signal 0.14%0.08% 8 He+ 9 Li BK/signal0.5%0.2%

Sensitivity to Sin 2 2  13 Reactor-related correlated error:  c ~ 2% Reactor-related uncorrelated error:  r ~ 1-2% Calculated neutrino spectrum shape error:  shape ~ 2% Detector-related correlated error:  D ~ 1-2% Detector-related uncorrelated error:  d ~ 0.5% Background-related error: fast neutrons:  f ~ 100%, accidentals:  n ~ 100%, isotopes( 8 Li, 9 He, …) :  s ~ 50-60% Bin-to-bin error:  b2b ~ 0.5% Many are cancelled by the near-far scheme and detector swapping

Sensitivity to Sin 2 2  13 Other physics capabilities: Supernova watch, Sterile neutrinos, …

Prototype: 45 PMT for 0.6 t LS

Backgrounds 60 Co spectrum Uniformity before correctionlinearity  2.5 MeV  2.5 In agreement with or better than expectation

Development of Gd-loaded LS LS (Gd0.1% Mesitylene 40% 60% bicron mineral oil) SampleAttenuation Lengths (m) 2: 8 mesitylene: dodecane （ LS ） 15.0 PPO 5g/L bis-MSB 10mg/L in LS % Gd-EHA in LS % Gd-TMHA in LS7.2 LAB~ PPO 5g/L bis-MSB 10mg/L in LAB % Gd-TMHA PPO 5g/L bis-MSB 10mg/L in LAB % Gd-EHA PPO 5g/L bis- MSB 10mg/L in 2: 8 mesitylene: LAB 14.1 IHEP and BNL both developed Gd-loaded LS using LAB: high light yield, high flash point, low toxicity, cheap, long attenuation length

Electronics for the prototype Readout module Readout Electronics

Aberdeen tunnel in HK: background measurement

North America (9) LBNL, BNL, Caltech, UCLA Univ. of Houston,Univ. of Iowa Univ. of Wisconsin, IIT, Univ. of Illinois-Urbana-champagne China (12) IHEP, CIAE,Tsinghua Univ. Zhongshan Univ.,Nankai Univ. Beijing Normal Univ., Shenzhen Univ., Hong Kong Univ. Chinese Hong Kong Univ. Taiwan Univ., Chiao Tung Univ., National United univ. Europe (3) JINR, Dubna, Russia Kurchatov Institute, Russia Charles university, Czech Daya Bay collaboration

Status of the project CAS officially approved the project Chinese Atomic Energy Agency and the Daya Bay nuclear power plant are very supportive to the project Funding agencies in China are supportive, R&D funding in China approved and available R&D funding from DOE approved Site survey including bore holes completed R&D started in collaborating institutions, the prototype is operational Proposals to governments under preparation Good collaboration among China, US and other countries

Schedule of the project Schedule – R&D, engineering design, secure funding – proposal, construction –2009 installation –2010 running

Summary Knowing Sin 2 2  13 to 1% level is crucial for the future of neutrino physics, particularly for the leptonic CP violation Reactor experiments to measure Sin 2 2  13 to the desired precision are feasible in the near future Daya Bay NPP is an ideal site for such an experiment A preliminary design is ready, R&D work is going on well, proposal under preparation