The Elusive Neutrinos –
neutrino oscillation, mixing and mass hierarchy
Yee Bob Hsiung 熊怡
National Taiwan University
March 4, 2014
@National Taiwan University
What is Neutrino?
什麼是微中子?
Discovery of neutrino
Reines &
Cowen
1956
Spin 1/2, nearly massless, neutral particle!
from neutron decay
(< 2.2 eV)
The Missing Solar Neutrinos
Some of the ν
efrom the sun
are missing.
Are Due to Neutrino Oscillation
SNO
ν e missing
but ν e + ν μ + ν τ agree
Theory
+ Higgs boson
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Kam-Biu Luk LP2011 9
Reactor-based ! 13 Experiments
RENO at Gonggwang, Korea
Daya Bay at Daya Bay, China
Double Chooz at Chooz, France
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28
13
Determining θ 13 With Reactor ν e
•
Look for disappearance of electron antineutrinos from reactors:
Large-amplitude oscillation due to θ12 Small-amplitude oscillation
due to θ13integrated over E
near detector
detector far
Disappearance probability!
R
FarR
Near=
L
NearL
Far!
"
# $
% &
2
N
FarN
Near!
"
# $
% & ε
Farε
Near!
"
# $
% & 1 − P
Far1− P
Near!
"
# $
% &
νe rate 1/r2
number of protons
detection
efficiency yield sin22θ13#
•
Perform a relative measurement:
sin22θ13 = 0.1
All correlated errors cancelled.
Yee Bob Hsiung
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12
Knowledge of θ 13 before 2012
PRL107,041801 (2011) PRL107, 181802 (2011)
arXiv:1112.6353
= 0.944±0.016±0.040 N
obsN
presin
22θ
13= 0.086±0.041±0.030
Double Chooz
T2K MINOS
Far-detector only
Some hints of a non-zero θ
131.7 σ#
2.5 σ over bkg 1.7 σ over bkg
Yee Bob Hsiung
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Kam-Biu Luk LP2011 10
The Daya Bay Collaboration
Europe (3) (10)
JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic
North America (16)(~100)
BNL, Caltech, LBNL, Iowa State Univ., Illinois Inst. Tech., Princeton, RPI, Siena,
UC-Berkeley, UCLA, Univ. of Cincinnati, Univ. of Houston,
Univ. of Wisconsin-Madison, Virginia Tech., Univ. of Illinois-Urbana-Champaign
Asia (19) (~140)
IHEP, Beijing Normal Univ., Chengdu Univ.
of Sci. and Tech., CGNPG, CIAE, Dongguan Polytech. Univ., Nanjing Univ., Nankai Univ.,
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.
~ 250 collaborators
台大, 交大 and 聯合 from Taiwan香港大學
Daya Bay Collaboration Meeting in CUHK
Kam-Biu Luk LP2011 11
Daya Bay Nuclear Power Complex
Daya Bay NPP
Ling Ao NPP Ling Ao II NPP
6 ! 2.95 GW
th= 17.7 GW
th• ~55 km from Hong Kong central
• All 6 reactors are in commercial operation
• one of top 5 most powerful nuclear
power plants in the world
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Kam-Biu Luk LP2011 12
Daya Bay reactors
Ling Ao reactors
Ling Ao II reactors
Daya Bay near
Ling Ao near
Water Hall
Far
Hall LS
Entrance
Construction tunnel
Target mass: 20t ! 4 Overburden: ~910mwe Event rate: (~90/day) ! 4 Muon rate: 0.04 Hz/m2
B/S: ~0.2% Target mass: 20t ! 2
Overburden: ~300mwe Event rate: (~740/day) ! 2 Muon rate: 0.73 Hz/m2 B/S: ~0.4%
Target mass: 20t ! 2 Overburden: ~270 mwe Event rate: (~840/day) ! 2 Muon rate: 1.2 Hz/m2 B/S: ~0.4%
Tunnel
Control Building
Surface Assembly Building (SAB)
m
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Daya Bay Detector Design
3m acrylic Vessel 192 PMTs
4m acrylic tank sandwiched between top and bottom reflectors Stainless steel
Tank
20t Gd-LS (target)
20t liquid scint.
(gamma catcher) 37t mineral
oil shield
5m 5m
Calibration units (LED, 68Ge,
AmC-Co)
Four layers of RPC’s to tag muons
2.5m water:
-
attenuates gamma rays & neutrons- forms two optically decoupled Cherenkov counters
Inner Cherenkov
Outer Cherenkov
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Detecting Reactor ν e
ν
ee
+γ
γ γ γ γ n
• Use the inverse
β-decay reaction in Gd-doped liquid scintillator:
ν
e+ p → e
++ n (prompt signal)
→ + p → D + γ (2.2 MeV) (delayed signal)
→ + Gd → Gd*
→ Gd + γ’s (8 MeV) (delayed signal)
~180µs
~30µs
for 0.1% Gd
• Time- and energy-tagged signal is a good tool to suppress background events.
• Energy of ν
eis given by:
E
ν≈ T
e++ T
n+ (m
n- m
p) + m
e+≈ T
e++ 1.8 MeV
10-40 keV
Yee Bob Hsiung
Interior of Antineutrino Detector
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3m IAVs produced in Taiwan
• All 3m inner acrylic vessels are produced in Taiwan
• 10mm thick wall, 15mm top /bottom covers
• Completely sealed with two penetration ports for Gd-LS filling and calibations.
• UV transparent down to 300nm wavelength
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Calibration System of Antineutrino Detectors
R=1.7725 m R=0 R=1.35m
3 sources for each z axis on a turntable (position accuracy < 5 mm):
• 10 Hz
68Ge (2×0.511 MeV γ’s)
• 0.5 Hz
241Am-
13C neutron source (3.5 MeV n without γ) + 100 Hz
60Co gamma source (1.173+1.332 MeV γ)
• LED diffuser ball (500 Hz) for PMT gain and timing
Three axes: center, edge of target, middle of gamma
catcher
213 Automatic calibration ‘robots’ (ACUs) on each detector
ACU-A ACU-B ACU-C
Yee Bob Hsiung
Stainless Steel Vessel (SSV) in assembly pit
Install Acrylic Vessels Install lower reflector
Install PMT ladders
Install top reflector
Close SSV lid
Install calibration units
22Assemble Antineutrino Detectors
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Liquid Scintillators
• Gd (0.1%) + PPO (3 g/L) + bis-MSB (15 mg/L) + LAB
• Number of proton:
(7.169±0034) × 10
25p per kg
• 185-ton Gd-LS + 196-ton LS production
185-t 0.1% Gd-LS stored in five 40-t tanks
A 1-m apparatus yielded attenuation length of ~15 m @ 430 nm.
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Fill Antineutrino Detectors (ADs)
• Target mass is measured with:
(1) 4 load cells supporting the 20-t ISO tank
(2) Coriolis mass flow meters Absolute uncertainty: 0.02%
Relative uncertainty: 0.02%
• Temperature is maintained constant
• Filling is monitored with in-situ sensors
ISO tank
Coriolis mass flow meters
Fill ADs with liquids
underground
Move AD into tunnel
Yee Bob Hsiung
Yee Bob Hsiung 25
Daya Bay Near Hall (EH1)
Install filled AD in pool Fill pool with purified water
Place cover over pool Roll RPC over cover
Data taking started on 15 Aug 2011
Getting Ling Ao Near and Far Halls Ready
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EH 2 (Ling Ao Near Hall):
Began operation on 5 Nov 2011
EH 3 (Far Hall):
Started data-taking on 24 Dec 2011
Yee Bob Hsiung
Triggers & Their Performance
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Discriminator threshold:
- ~0.25 p.e . for PMT signal
Triggers:
- AD: ≥ 45 PMTs (digital trigger) ≥ 0.4 MeV (analog trigger)
- Inner Water Cherenkov: ≥ 6 PMTs
- Outer Water Cherenkov: ≥ 7 PMTs (near) ≥ 8 PMTs (far) - RPC: 3/4 layers in each module
Trigger rate:
- AD: < 280 Hz
- Inner Water Cherenkov: < 160 Hz
- Outer Water Cherenkov: < 200 Hz
Energy Calibration
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Gain vs. time
60
Co at center
Energy vs. position
Light yield: ~163 p.e./MeV
Selecting Antineutrino (IBD) Candidates
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Use Prompt + Delayed correlated signal to select antineutrino candidates.
Selection:
-
Prompt: 0.7 MeV < E
p< 12 MeV -
Delayed: 6.0 MeV < E
d< 12 MeV -
Capture time: 1 μ s < Δ t < 200 μ s -
Reject Flashers
- Muon Veto:
Pool Muon: Reject 0.6ms
AD Muon (>20 MeV): Reject 1ms
AD Shower Muon (>2.5GeV): Reject 1s - Multiplicity:
No other signal > 0.7 MeV
in -200 μs to 200 μs of IBD.
From Bemporad, Gratta and Vogel
Arbitrary
Flux Cross Section νe spectrum
(no oscillation)
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