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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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
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
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
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
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
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
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
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