Daya Bay - University of Oxford Department of Physics

Daya Bay Experiment and
the Future of
Chinese Neutrino Physics Program
Yifang Wang
Institute of High Energy Physics
Oxford, March 4, 2014
Neutrinos around us
Supernova
Astrophysics
Geology
Human body
Cosmology
Accelerator
Galaxy
Nuclear physics
Particle physics
Sun
Big Bang
2014-3-7
Reactor
Earth
2
Neutrinos

Fundamental building blocks of matter:
e  


   

 e 


u

d
c t

s b
Abundant: 300/cm3 in the Universe, same as photons
Mass: the central issue of neutrino physics
 Although tiny, very important to the universe
 Not massless: Only evidence beyond the Standard Model of
particle physics

Neutrinos and cosmology
 Part of dark matter
 Related to matter-antimatter asymmetry
 Related to the universe evolution, large scale structure, …
2014-3-7
3
Neutrinos are useful

Neutrino astronomy





Proved the solar model
Supernovae study
Neutrinos from deep Universe
Cosmic-rays
Neutrino geology
 Earth thermal emission
 U/Th ratio in earth
 Neutrino beams through earth: CT ?

Rector monitoring
2014-3-7
4
Neutrino Oscillation

If the neutrino mass eigenstate is different from that of the
weak interaction, neutrinos can oscillate: from one type to
another during the flight:
e
Oscillation
probability：

e

P(e->) = sin2(2q) sin2(1.27Dm2L/E)
Oscillation
amplitude
Oscillation
frequency
Oscillation matrix
for 3 generations：
 Known parameters： q23，q12，DM223， DM212，
 Recent progress: q13
 Unknown parameters: mass hierarchy(DM223), CP phase d
2014-3-7
5
Daya Bay: for a New Type of Oscillation
q12 Solar 
Oscillation
q23 Atm. 
Oscillation



1
2
3
q13 ?
Fundamental principles
Fundamental parameter
Direction of future neutrino
physics:

2014-3-7
If q13 is too small，CPV cannot
be figured out in the near future
CPV can be measured by
Pe ≈ sin2q23sin22q13sin2(1.27Dm223L/E)
+ cos2q23sin22q12sin2(1.27Dm212L/E)
- A(r)cos2q13sinq13sin(d)
6
Direct Searches in the Past

Palo Verde & Chooz: no signal
Sin22q13 < 0.15 @ 90%C.L.
if DM223 = 0.0024 eV2

T2K: 2.5 s over bkg（2011）
0.03 < Sin22q13 < 0.28 @ 90%C.L. for NH
0.04 < Sin22q13 < 0.34 @ 90%C.L. for IH

Minos: 1.7 s over bkg（2011）
0 < Sin22q13 < 0.12 @ 90%C.L. NH
0 < Sin22q13 < 0.19 @ 90%C.L. IH

Allowed region
Sin22q13 prediction
Double Chooz: 1.7 s（2011）
sin22θ13=0.086±0.041(stat)±0.030(sys)
2014-3-7
7
Experiments with neutrinos from reactors

Huge production yield：
6 1020  /s @ 3 GW

Powerful background
rejection capability：
e  p  e  n

Neutrino energy:
E  Te  Tn  ( M n - M p )  me

10-40 keV
2014-3-7
1.8 MeV: Threshold
8
Reactor Experiments: comparing
observed/expected neutrinos
Precision of past experiments，
typically 3-6%

Reactor power: ~ 1%
Spectrum: ~ 0.3%
Fission rate: 2%

Backgrounds: ~1-3%

Target mass: ~1-2%
Efficiency: ~ 2-3%


Pee  1 - sin22q13sin2 (1.27Dm213L/E) -

cos4q13sin22q12sin2 (1.27Dm212L/E)
Our design goal：a precision of ~ 0.4%
2014-3-7
9
Daya Bay Experiment: Layout
Redundancy !!!

Relative measurement to cancel Corr. Syst. Err.
 2 near sites, 1 far site

Multiple AD modules at each site to reduce Uncorr. Syst. Err.
 Far: 4 modules，near: 2 modules

Cross check; Reduce errors by 1/N
Multiple muon detectors to reduce veto eff. uncertainties
 Water Cherenkov： 2 layers
 RPC： 4 layers at the top + telescopes
2014-3-7
10
Comparison with others
Experiment
Luminosity
(t  GW)
Detector
uncertainty
Overburden
(Near/far)(MWE)
Sensitivity
(90%CL)
Daya Bay
1400
0.38%/√N
250 / 860
~ 0.008
Double Chooz
70
0.6%
120 / 300
~ 0.03
260
0.5%
120 / 450
~ 0.02
RENO
• Higher luminosity
 Faster to accumulate statistics
• Smaller systematics (in fact 0.2%√N)
Daya Bay
Reno
Double
Chooz
 Higher precision
• More overburden
 Less backgrounds
2014-3-7
Huber et al. JHEP 0911:044, 2009 11
The Daya Bay Collaboration
Europe (2)
JINR, Dubna, Russia
Charles University, Czech Republic
North America (16)
BNL, Caltech, LBNL, Iowa State Univ.,
Illinois Inst. Tech., Princeton, RPI,
UC-Berkeley, UCLA, Univ. of Cincinnati,
Univ. of Houston, Univ. of Wisconsin,
William & Mary, Virginia Tech.,
Univ. of Illinois-Urbana-Champaign, Siena
~250 Collaborators
2014-3-7
Asia (20)
IHEP, Beijing Normal Univ., Chengdu Univ.
of Sci. and Tech., CGNPG, CIAE, Dongguan
Polytech. Univ., Nanjing Univ., Nankai Univ.,
NCEPU, Shandong Univ., Shanghai Jiao tong
Univ., Shenzhen Univ.,
Tsinghua Univ., USTC, Zhongshan Univ.,
Univ. of Hong Kong, Chinese Univ. of Hong Kong,
National Taiwan Univ., National Chiao Tung Univ.,
National United Univ.
12
Timeline of the Experiment







Aug. 2003: Experimental plan and the detector design is proposed
2006: Project approved in China, and afterwards in other countries
Oct. 2007: Civil construction started
Dec.2010: All the blasting for the tunnel and underground hall completed
2008-2011: Detector construction, assembly and installation
Aug. 2011: Near detector data taking started
Dec. 2011: Far detector data taking started  full detector data taking
Opening ceremony：Oct. 2007
2014-3-7
13
Tunnel and Underground Lab
•Tunnel:
~ 3100m
•3 Exp. hall
•1 hall for LS
•1 hall for water
A total of ~ 3000
blasting right next
reactors. No one
exceeds safety limit
set by National
Nuclear Safety
Agency（0.007g）
2014-3-7
14
Anti-neutrino Detector (AD)

Three zones modular structure:
I. target: Gd-loaded scintillator
II. g-catcher: normal scintillator
III. buffer shielding: oil


192 8” PMTs/module
Two optical reflectors at the top
and the bottom, Photocathode
coverage increased from 5.6% to 12%
~ 163 PE/MeV
Target: 20 t, 1.6m
g-catcher: 20t, 45cm
Buffer: 40t, 45cm
Total weight: ~110 t
2014-3-7
15
Detector Assembly
SSV
Top reflector
2014-3-7
SSV lid
Bottom reflector
PMT
Leak check
4m AV
3m AV
ACU
16
Challenge: Gd-loaded Liquid Scintillator

Liquid production, QA, storage
and filling at Hall 5

 185t Gd-LS, ~180t LS, ~320t oil
LAB+Gd (TMHA)3+PPO+BisMSB

Stable over time
 Light yield: ~163 PE/MeV
Stable Liquid
Liquid hall：LS production and filling
2014-3-7
17
Water Cerenkov Detector Installation
PermaFlex painting
Install AD
2014-3-7
PMT frame & Tyvek
Pool with water
Completed pool
Cover
18
Hall 1(two ADs) Started Operation on Aug. 15, 2011
2014-3-7
19
One AD insalled in Hall 2
Physics Data Taking Started on Nov.5, 2011
2014-3-7
20
Three ADs installed in Hall 3
Physics Data Taking Started on Dec.24, 2011
2014-3-7
21
Daya Bay：Data taking & analysis status
Two detector comparison
[1202.6181]
• 90 days of data, Daya Bay near only
• NIM A 685 (2012), 78-97
First oscillation analysis
[1203:1669]
• 55 days of data, 6 ADs near+far
• PRL 108 (2012), 171803
Improved oscillation analysis [1210.6327]
• 139 days of data, 6 ADs near+far
• CP C 37 (2013), 011001
Spectral Analysis
arXiv:1310.6732
• 217 days complete 6 AD period
• 55% more statistics than CPC result
• Reported at NuFACT’2013, paper
submitted
2014-3-7
22
Event Signature and Backgrounds

Signature:
 e  p  e  n
 Prompt: e+, 1-10 MeV,
 Delayed: n, 2.2 MeV@H, 8 MeV @ Gd
 Capture time: 28 s in 0.1% Gd-LS

Backgrounds
 Uncorrelated: random coincidence of gg, gn or nn


g from U/Th/K/Rn/Co… in LS, SS, PMT, Rock, …
n from a-n, -capture, -spallation in LS, water & rock
 Correlated:




2014-3-7
Fast neutrons: promptn scattering, delayed n capture
8He/9Li: prompt b decay, delayed n capture
Am-C source: prompt g rays, delayed n capture
a-n: 13C(α,n)16O
23
Neutrino Event Selection

Pre-selection
 Reject Flashers
 Reject Triggers within (-2 μs, 200 μs) to a tagged water pool muon

Neutrino event selection
 Multiplicity cut
 Prompt-delayed pairs within a time interval of 200 μs
 No triggers(E > 0.7MeV) before the prompt signal and after the
delayed signal by 200 μs
 Muon veto
 1s after an AD shower muon
 1ms after an AD muon
 0.6ms after an WP muon
 0.7MeV < Eprompt < 12.0MeV
 6.0MeV < Edelayed < 12.0MeV
 1μs < Δte+-n < 200μs
2014-3-7
24
Signal+Backgound Spectrum
EH1
138835 signal
candidates
66473 signal
candidates
EH3
B/S @EH1/2 B/S @EH3
28909 signal
candidates
2014-3-7
Accidentals
~1.4%
~4.5%
Fast neutrons
~0.1%
~0.06%
8He/9Li
~0.4%
~0.2%
Am-C
~0.03%
~0.3%
a-n
~0.01%
~0.04%
Sum
~2%
~5%
25
Daily Neutrino Rate


Three halls taking data synchronously allows near-far
cancellation of reactor related uncertainties
Rate changes reflect the reactor on/off.
Prediction:



Baseline（ 3.5cm，
~0.002%）
Target mass（3kg，
0.015%）
Reactor neutrino flux
Predictions are absolute,
multiplied by a
normalization factor from
the fitting
2014-3-7
26
The Most Precise Neutrino Experiment
Side-by-side Comparison
Design：(0.18 - 0.38) %
2014-3-7
Expectation:
R(AD1/AD2) = 0.981
Measurement:
0.984  0.004(stat) 
0.002(syst)
27
A New Type of Oscillation Discovered

Observation of electron anti-neutrino disappearance:
announced on
R = 0.940 ±0.011 (stat) ±0.004 (syst)
Mar. 8, 2012
Sin22q13 = 0.092  0.016(stat)  0.005(syst)
c2/NDF = 4.26/4, 5.2 σ for non-zero θ13
2014-3-7
F.P. An et al., NIM. A 685(2012)78
F.P. An et al., Phys. Rev. Lett. 108,
(2012) 171803
28
Energy Response Model
Mapping the true energy
Etrue to the reconstructed
kinetic energy Erec:



Build models taking into account:
 Electronics non-linearity: timedependent charge collection
efficiency
 Scintillator non-linearity: Quench
effect & Cerenkov radiation
 Complicated e+,e-, g’s interactions
in LS， from simulation
Constraint parameters by a fit to all
calibration data
Model difference  systematic errors
2014-3-7
arXiv:1310.6732
29
Prompt IBD spectra (~E)
2014-3-7
30
Pure Spectral Analysis
θ13 = 0 can be excluded at > 3σ from spectral information alone
2014-3-7
31
Rate+Spectra Oscillation Results
arXiv:1310.6732
2014-3-7
32
Global Comparison of θ13 Measurements
Be careful to take the average:
 Correlated errors
 Error estimate
The three reactor experiments will work together to report results in
2014-3-7a coherent way, and probably can report a combined result.
33
Current status and future plan

Summer(2012) maintenance
completed
 Two new AD modules installed
 Special Automatic & Manual
calibration completed


Data taking resumed in Oct.
Precision results in three
years, D(sin22q13) ~ 4%
2014-3-7
34
Still a lot of unknowns

Neutrino oscillation：










2014-3-7
Neutrino mass hierarchy ?
Unitarity of neutrino mixing matrix ？
Θ23 is maximized ?
CP violation in the neutrino mixing matrix as in the case of
quarks ? Large enough for the matter-antimatter asymmetry in
the Universe ?
What is the absolute neutrino mass ?
Neutrinos are Dirac or Majorana ?
Are there sterile neutrinos？
Do neutrinos have magnetic moments ？
Can we detect relic neutrinos ?
……
35
Next Experiment: JUNO
Daya Bay
Huizhou
Lufeng
Yangjiang
Taishan
Status Operational Planned
Planned
Under construction
Under construction
Power 17.4 GW
17.4 GW
17.4 GW
18.4 GW
17.4 GW
Overburden ~ 700 m
Daya Bay
JUNO
Site 2
Huizhou
Lufeng
Daya Bay
Site 1
Taishan
Yangjiang
2014-3-7
Talk by Y.F. Wang at ICFA seminar 2008, Neutel
2011; by J. Cao at Nutel 2009, NuTurn 2012 ;
Paper by L. Zhan, Y.F. Wang, J. Cao, L.J. Wen,
PRD78:111103,2008; PRD79:073007,2009 36
The plan: a large LS detector
–
–
LS volume:  20 for more mass & statistics
light(PE)  5 for resolution
Muon detector
Steel Tank
20 kt LS
Water seal
20kt water
Acrylic tank：F34.5m
Stainless Steel tank ：F37.5m
6kt MO
~15000 20” PMTs
coverage: ~80%
1500 20” VETO PMTs
2014-3-7
37
Physics Reach
Thanks to a large θ13
• Mass hierarchy
• Precision measurement of
mixing parameters
• Supernova neutrinos
• Geoneutrinos
• Sterile neutrinos
• ……
Current
Daya Bay II
Dm212
3%
0.6%
Dm223
5%
0.6%
sin2q12
5%
0.7%
sin2q23
5%
N/A
14% 4%
~ 15%
2
2014-3-7sin q13
Detector size: 20kt
Energy resolution: 3%/E
Thermal power: 36 GW
Y.F. Li et al., arXiv:1303.6733
For 6 years，mass hierarchy cab
be determined at 4s level, if Δm2
can be determined at 1% level
38
Detector design



LS detector in the water pool: No Gd-loading
Estimated signal event rate: 40/day
Backgrounds:
 Accidentals(~10%), 9Li/8He(<1%), fast neutros(<1%)

Several detector options:
 Acrylic ball + unistruct for PMT
 Steel ball + acrylic blocks
 Steel ball + acrylic walls + Balloon
 …



R&D one the way
Design choice by 2014
Prototype will be started soon
2014-3-7
39
Liquid Scintillator
 Longer
attenuation length: 15m
 30m
 Improve raw materials (using Dodecane
instead of MO for LAB production）
 Improve the production process
 Purification
 Higher
light yield
 fluor concentration optimization
LIght output, relative units
1,0
0,8
0,6
0,4
0,2
KamLAND
0,0
0,0
0,1
2014-3-7
0,2
0,3
0,4
0,5
PPO mass fraction, %
0,6
Linear Alky
Benzene
Atte. L(m) @
430 nm
RAW
14.2
Vacuum
distillation
19.5
SiO2 coloum
18.6
Al2O3 coloum
LAB from Nanjing,
Raw
Al2O3 coloum, fourth
time
Al2O3 coloum,
second time
Al2O3 coloum, 8th
time
22.3
20
27
25
24
0,7
40
High QE MCP-PMT

Prototypes
underway
SPE
QE
2014-3-7
41
Test results of a prototype
2014-3-7
42
Site selection
• Site is determined, configuration is finalized
– A vertical shaft(600 m) + sloped tunnel(1300m)
• Overburden: ~ 700 m
2014-3-7
43
Status of the project


Conceptual design & R&D plan
approved in China
Site determined, geological survey
completed
 Rock: High quality granite
 No water leak
 Rock Tem. ~ 31 oC

Detailed civil design underway
 Bidding process started
 Winner(for design and construction)
will be determined on April 1


2014-3-7
Paper work to get construction
permission underway
Collaboration will be established
soon
44
Brief schedule







Civil preparation：2013-2014
Civil construction：2015-2017
Detector R&D：2013-2016
Detector component production：2016-2017
PMT production：2016-2019
Detector assembly & installation：2018-2019
Filling & data taking：2020
After a number of reviews, we are approved by the
CAS(~ CD1)
R&D funding is available
2014-3-7
45
A New Type of Neutrino Beam for CP (MOMENT)
Detector
Detector：
 Flavor sensitive
 Charge sensitive
 NC/CC sensitive
2014-3-7
Neutrinos after the
target/ collection/decay:
〉1021 /year
46
Comparison
 Factory
Super pi beam
MOMENT
Neutrino energy
2-4 GeV
0.3-0.7，2-4 GeV
300 MeV
Neutrino source
Muon decay
Pi decay
Muon decay
high
low
Beam backgrounds no
Neutrino flux
1021/year
1018-21/year
51021/year
Proton driver
Pulsed
8-16 GeV
4 MW
Pulsed
5-400 GeV
1-5 MW
CW
1.5 GeV
15 MW
Target
Mercury
Mercury
?
Collection
Horn
Horn
SC magnet
Decay pipe
Storage ring
Vacuum pipe
SC magnet
cooling
yes
No
No
Muon acceleration
yes
No
No
cost
High
low
low
2014-3-7
47
Best energy for CP ?
• Below in-elastic threshold: ~ 300 MeV  baseline = 150 km
• Such a threshold is similar for CC/NC & /bar
• Although we loose statistics due to the lower cross section,
but we have less systematics by being p0 free
J.Formaggio and G.Zeller,
Rev. Mod.Phys. 84.3(2012)1307
2014-3-7
48
Summary
• Neutrino physics is very promising in the next
decades
• Daya Bay experiment is the start of neutrino
physics in China
• JUNO will bring us to a new stage
• MOMENT is still under study. Hopefully it can
be developed into a real project
• We are looking for collaborators
2014-3-7
49