Measuring sin2213 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/cm3 , about 0.3% -1% of the total mass of the universeMost 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 neutrinosImportant to the formation of the large structure of the universe, may explain why there is no anti-matter in the universe

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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 oscillation1968 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 massA new window for particle physics, astrophysics, and cosmology

Neutrino oscillation: PMNS matrix

EXOGeniusCUORENEMO

A total of 6 parameters: 2 m2, 3 angles, 1 phases+ 2 Majorana phases

If Mass eigenstates Weak eigenstates Neutrino oscillationOscillation probability ： Psin2(1.27m2L/E)

Atmospheric solar decays

crossing ： CP 与 13

Super-KK2KMinosT2K

Daya BayDouble ChoozNOVA

HomestakeGallexSNOKamLAND

Evidence of Neutrino Oscillations

Unconfirmed:LSND:m2 ~ 0.1-10 eV2

Confirmed:Atmospheric:m2 ~ 210-3 eV2

Solar:m2 ~ 8 10-5 eV2

Psin22sin2(1.27m2L/E)2 flavor oscillation in vacuum:

A total of six mixing parameters ：Known ： | m2

32|, sin2232 --Super-K

m221, sin2221 --SNO,KamLAND

Unknown ： sin22 ， , sign of m232

at reactors:

Pee 1 sin22sin2 (1.27m2L/E)

cos4sin22sin2 (1.27m2L/E)

at LBL accelerators:

Pe ≈ sin2sin22sin2(1.27m2L/E) +

cos2sin22sin2(1.27m212L/E)

A()cos213sinsin()

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

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0.1 1 10 100

Nos

c/Nn

o_os

c

Baseline (km)

Small-amplitude

oscillation due to 13

Large-amplitude

oscillation due to 12

Current Knowledge of 13

Global fitfogli etal., hep-ph/0506083

Sin2(213) < 0.09

Sin2(213) < 0.18

Direct search PRD 62, 072002

Allowed region

• No good reason(symmetry) for sin2213 =0

• Even if sin2213 =0 at tree level, sin2213 will not vanish at low energies with radiative corrections

• Theoretical models predict sin2213 ~ 0.1-10 %

An experiment with a precision for sin2213 less than 1% is desired

model prediction of sin2213

Experimentally allowedat 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 sin22 ， next generation LBL experiment for CP

– If sin22next generation LBL experiment for CP ???

4 ） provide direction to the future of the neutrino physics: super-neutrino beams or neutrino factory ?

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Recommendation of APS study report:

2004.11.4 APS

How to do this experiment

How Neutrinos are produced in reactors ?

The most likely fissionproducts 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 GWthermal : 6 1020 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., PLB218,365P. 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 235U, 239Pu, 241Pu and 238U

235U, 239Pu, 241Pu from their measured spectra

238U(10%) from calculation (10%)

• They all agree well within 3%

nepe

10-40 keV

Neutrino energy:

Neutrino Event: coincidence in time, space and energy

epnnemMMTTE )(

neutrino detection: Inverse-β reaction in liquid scintillator

1.8 MeV: Threshold

，，

ors(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 comparisonChooz Palo Verde KamLAN

DDaya Bay

Reactor power 0.7 0.7 2.05 <0.1%

Reactor fuel/spectra 2.0 2.0 2.7

cross section 0.3 0.2 0.2 0

No. of protons H/C ratio 0.8 0.8 1.7 0.2 0

Mass - - 2.1 0.2 0

Efficiency Energy cuts 0.89 2.1 0.26 0.2

Position cuts 0.32 3.5 0

Time cuts 0.4 0. 0.1

P/Gd ratio 1.0 - 0.1

n multiplicity 0.5 - <0.1

background correlated 0.3 3.3 1.8 0.2

uncorrelated 0.3 1.8 0.1 <0.1

Trigger 0 2.9 0 <0.1

livetime 0 0.2 0.2 0.03

xperi

Angra, Brazil

Diablo Canyon, USA

Braidwood, USAChooz, 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)

8.7 150/1067 10/10 60/300 ~ 0.03

Daya Bay

(China)

11.6 360/500/1800 40/40/80 260/260/910 ~ 0.008

Kaska

(Japan)

24.3 350/1600 6/6/2 6 90/90/260 ~ 0.02

Reno

(S. Korea)

17.3 150/1500 20/20 230/675 ~ 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

2

22 2

1 1,3

2 2 22 2 2

2 2 2 2 2 21 1,3

(1 )

min

rAA A A A Aii i D c d i r iANbin

r iA A As

i A i i b i

A ANbinc i dD r

r i AD c r shape d B

TM T c b B

T

T T B

c b

Best location for far detectors

Rate only Rate + shape

Total Tunnel length3200 m

Detector swapping in a horizontal tunnel cancels most detector systematic error. Residual error ~0.2%

BackgroundsB/S of DYB,LA ~0.5%B/S of Far ~0.2%

Fast MeasurementDYB+Mid, 2008-2009Sensitivity (1 year) ~0.03

Full MeasurementDYB+LA+Far, from 2010Sensitivity (3 year) <0.01

The Layout

LA: 40 tonBaseline: 500mOverburden: 98mMuon rate: 0.9Hz/m2

Far: 80 ton1600m to LA, 1900m to DYBOverburden: 350mMuon rate: 0.04Hz/m2

DYB: 40 tonBaseline: 360mOverburden: 97mMuon rate: 1.2Hz/m2

Access portal

Waste transport portal

8% slope

0% slope

0% slope

0% slopeMid: Baseline: ~1000mOverburden: 208m

Geologic survey completed, including

boreholes

Weathering bursa ( 风化囊）

Faults(small)

far

near

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 ~ 15-24 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 sitesFour 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 = 5%@8MeV, s ~ 14 cm

I

IIIII

Isotopes Purity(ppb)

20cm(Hz)

25cm (Hz)

30cm(Hz)

40cm(Hz)

238U(>1MeV) 50 2.7 2.0 1.4 0.8232Th(>1MeV)

50 1.2 0.9 0.7 0.4

40K(>1MeV) 10 1.8 1.3 0.9 0.5

Total 5.7 4.2 3.0 1.7

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 UkraineContribution 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 rate @ 0.9MeV < 50Hz

single neutron rate < 1000/day

2m water + 50 cm oil shielding

– Correlated backgrounds: n E0.75

Neutrons: >100 MWE + 2m water

Y.F. Wang et al., PRD64(2001)0013012 8He/9Li: > 250 MWE(near) &

>1000 MWE(far) T. Hagner et al., Astroparticle. Phys.

14(2000) 33

Fast neutron spectrum

Precision to determine the 9Li background in situ

Spectrum of accidental background

Background estimated by GEANT MC simulation

Near far

Neutrino signal rate(1/day) 560 80

Natural backgrounds(Hz) 45.3 45.3

Single neutron(1/day) 24 2

Accidental BK/signal 0.04% 0.02%

Correlated fast neutron Bk/signal

0.14% 0.08%

8He+9Li BK/signal 0.5% 0.2%

Sensitivity to Sin2213

• 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(8Li, 9He, …) : s ~ 50-60%

• Bin-to-bin error: b2b ~ 0.5%

2

22 2

1 1,3

2 2 22 2 2

2 2 2 2 2 21 1,3

(1 )

min

rAA A A A Aii i D c d i r iANbin

r iA A As

i A i i b i

A ANbinc i dD r

r i AD c r shape d B

TM T c b B

T

T T B

c b

Many are cancelled by the near-far scheme and detector swapping

Sensitivity to Sin2213

Other physics capabilities:Supernova watch, Sterile neutrinos, …

Prototype: 45 PMT for 0.6 t LS

Backgrounds 60Co spectrum

Uniformity before correction linearity

56%5 MeV

In agreement with or better than expectation

Development of Gd-loaded LSLS (Gd0.1% Mesitylene 40%60% bicron mineral oil)Sample Attenuation

Lengths (m)

2: 8 mesitylene: dodecane （ LS ）

15.0

PPO 5g/L bis-MSB 10mg/L in LS

11.3

0.2% Gd-EHA in LS 8.3

0.2% Gd-TMHA in LS 7.2

LAB ~

PPO 5g/L bis-MSB 10mg/L in LAB

23.7

0.2% Gd-TMHA PPO 5g/L bis-MSB 10mg/L in LAB

19.1

0.2% 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

From PMT

-5V

50Ω High speedAmp.

AD8132

10KΩ

10pF

10bit/40MSPSFlash ADC

FPGA

To VME bus

1K

1K

CH16

CH1

+-

1K

Energy sum to trigger module

AD8065

SUM

integrator

DAC

threshold

start

stop

`

CH2

Disc.

L1 Trigger (LVPECL)

TDC

Pipeline

40MHz Clock (LVPECL)

charge

time

DATABUFFER

L1

VMEinterface

Single channel macro in FPGA

X 16

Test input

+-

AD9215

RC=100ns

RC2+

-

RC=50ns

Single ended to diff.

10bit

CL

K

CL

KC

LK200ns width < 1µs width

resol.: 0.5ns

< 300ns width

10ns width

Amp.

S2D

10pF

50Ω

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– 2004-2006 R&D, engineering design,

secure funding– 2007-2008 proposal, construction– 2009 installation– 2010 running

Summary• Knowing Sin2213 to 1% level is crucial for

the future of neutrino physics, particularly for the leptonic CP violation

• Reactor experiments to measure Sin2213 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