changgen yang institute of high energy physics, beijing for the daya bay collaboration
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Changgen Yang
Institute of High Energy Physics, Beijingfor the Daya Bay Collaboration
Daya Bay Neutrino Experiment
International UHE Tau Neutrino Workshop, April 24-26, 2006
13The Last Unknown
Neutrino Mixing Angle UMNSP Matrix
U Ue1 Ue2 Ue3
U1 U2 U 3
U1 U 2 U 3
1 0 0
0 cos23 sin23
0 sin23 cos23
cos13 0 e iCP sin13
0 1 0
e iCP sin13 0 cos13
cos12 sin12 0
sin12 cos12 0
0 0 1
1 0 0
0 e i / 2 0
0 0 e i / 2i
?
atmospheric, K2K reactor and accelerator 0SNO, solar SK, KamLAND
12 ~ 32° 23 = ~ 45° 13 = ?
Large and maximal mixing!
?
• What ise fraction of 3?• Ue3 is a gateway to CP violation in neutrino sector: P( e) - P( e) sin(212)sin(223)cos2(13)sin(213)sin
13 from Reactor and Accelerator Experiments
Pee 1 sin2 213 sin2 m312L
4E
cos4 13 sin2 212 sin2 m21
2L
4E
- Clean measurement of 13
- No matter effects
CP violation
mass hierarchy
matter
reactor
accelerator
- sin2213 is missing key parameter for any measurement of CP
Current Knowledge of 13
Direct search
At m231 = 2.5 103 eV2,
sin22 < 0.15
allowed region
Fogli etal., hep-ph/0506083
Sin2(213) < 0.09
Sin2213 < 0.18
Best fit value of m232 = 2.4103
eV2
Global fit
Limitations of Past and CurrentReactor Neutrino Experiments
Palo Verde, CHOOZTypical precision is 3-6%
due to• limited statistics• reactor-related systematic
errors:
- energy spectrum of e
(~2%)
- time variation of fuel
composition (~1%)• detector-related systematic
error (1-2%)• background-related error
(1-2%)
Daya Bay: Goals And Approach• Utilize the Daya Bay nuclear power facilities to:
- determine sin2213 with a sensitivity of 1%- measure m2
31
• Adopt horizontal-access-tunnel scheme:
- mature and relatively inexpensive technology- flexible in choosing overburden and changing baseline- relatively easy and cheap to add experimental halls- easy access to underground experimental facilities - easy to move detectors between different
locations with good environmental control.
• Employ three-zone antineutrino detectors.
How To Reach A Precision of 0.01 ?
• Powerful nuclear plant • Larger detectors
• “Identical” detectors
• Near and far detectors to minimize reactor-related errors
• Optimize baseline for best sensitivity and smaller residual reactor-related errors
• Interchange near and far detectors – cancel many detector systematic errors
• Sufficient overburden/shielding to reduce background
• Comprehensive calibration/monitoring of detectors
Ling Ao II NPP:2 2.9 GWth
Ready by 2010-2011
Ling Ao NPP:2 2.9 GWth
Daya Bay NPP:2 2.9 GWth
1 GWth generates 2 × 1020 e per sec
55 k
m
45 km
The Daya Bay Nuclear Power Facilities
• 12th most powerful in the world (11.6 GW)• Top five most powerful by 2011 (17.4 GW)• Adjacent to mountain, easy to construct tunnels to reach underground labs with sufficient overburden to suppress cosmic rays
Where To Place The Detectors ?
P(e e ) 1 sin2 213 sin2 m312 L
4E
cos4 13 sin2 212 sin2 m21
2 L
4E
• Place near detector(s) close to reactor(s) to measure raw flux and spectrum of e, reducing reactor-related systematic
• Position a far detector near the first oscillation maximum to get the highest sensitivity, and also be less affected by 12
• Since reactor e are low-energy, it is a disappearance experiment:
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)
Large-amplitudeoscillation due to
12
Small-amplitudeoscillation due to 13
neardetector
fardetector
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
Daya BayNPP
Ling AoNPP
Ling Ao-ll NPP(under const.)
Entrance portal
Empty detectors: moved to underground halls through access tunnel.Filled detectors: swapped between underground halls via horizontal tunnels.
Total length: ~2700 m
230 m(15% slope)290 m
(8% slope) 73
0 m
570 m
910 m
Daya Bay Near360 m from Daya BayOverburden: 97 m
Ling Ao Near500 m from Ling AoOverburden: 98 m
Far site1600 m from Ling Ao2000 m from DayaOverburden: 350 m
Mid site~1000 m from DayaOverburden: 208 m
A Versatile Site• Rapid deployment:
- Daya Bay near site + mid site - 0.7% reactor systematic error
• Full operation: (A) Two near sites + Far site (B) Mid site + Far site (C) Two near sites + Mid site + Far site Internal checks, each with different systematic
Geophysical profile (Daya–mid--far)
Bore Samples Zk4 (depth: 133 m)
Zk2 (depth: ~180 m)
Zk3 (depth: ~64 m) Zk1 (depth: 210 m)
At tunneldepth
Findings of Geotechnical Survey
• No active or large fault• Earthquake is infrequent• Rock structure: massive and blocky
granite• Rock mass: most is slightly
weathered or fresh• Groundwater: low flow at the depth of
the tunnel• Quality of rock mass: stable and hard
Good geotechnical conditions for tunnel construction
Detecting Low-energy e
e p e+ + n (prompt)
+ p D + (2.2 MeV) (delayed)
+ Gd Gd* Gd + ’s(8 MeV) (delayed)
• Time- and energy-tagged signal is a good tool to suppress background events.
• Energy of e is given by:
E Te+ + Tn + (mn - mp) + m e+ Te+ + 1.8 MeV 10-40 keV
• The reaction is the inverse -decay in 0.1% Gd-doped liquid scintillator:
Arb
itra
ry
Flux Cross
Sectio
n
Observable Spectrum
From Bemporad, Gratta and Vogel
0.3b
50,000b
What Target Mass Should Be?
Systematic errorBlack : 0.6%
DYB: B/S = 0.5% LA: B/S = 0.4% Far: B/S = 0.1%
m231 = 2 10-3 eV2
tonnes
(3 year run)
Red : 0.25% (baseline goal)Blue : 0.12%
Design of Antineutrino Detectors• Three-zone structure:
I. Target: 0.1% Gd-loaded liquid scintillatorII. Gamma catcher: liquid scintillator, 45cmIII. Buffer shielding: mineral oil, ~45cm
• Possibly with diffuse reflection at ends. ~200 PMT’s around the barrel:
Isotopes(from PMT)
Purity
(ppb)
20cm
(Hz)
25cm (Hz)
30cm
(Hz)
40cm
(Hz)
238U(>1MeV) 50 2.7 2.0 1.4 0.8
232Th(>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
Oil buffer thickness
buffer
20 tonne
s
Gd-LS
gamma catchervertex
14%~ , 14cm
(MeV)
E E
Why three zones ?
3-ZONE 2-ZONE
n capture on Gd yields 8 MeV with 3-4 ’s
Chooz
background
• 3 zones provides increased confidence in systematic error associated with detection efficiency and fiducial volume
• 2 zones implies simpler design/construction, some cost reduction but with increased risk to systematic error
Gd-loaded Liquid Scintillator For Daya BayA
bso
rban
ce a
t 43
0 n
m
Calendar Date
507 days (1.2% Gd in PC)
455 days (0.2% Gd in PC)367 days (0.2% Gd in 20% PC + 80% C12H26)130 days (0.2% Gd in LAB)
• Require stable Gd-loaded liquid scintillator with - high light yield- long attenuation length
• BNL/IHEP/JINR nuclear chemists study on metal-loaded liquid scintillator (~1% Gd diluted to ~0.1% Gd) for Daya Bay:
- technology of 1% Gd in pseudocumene (PC) is mature- need R&D for 1% Gd in mixture of PC and dodecane, and with linear alkyl benzene (LAB)
Attenuation lengths > 15 m
BNL samples
Design of Shield-Muon Veto
• Detector modules enclosed by 2m of water to shield neutrons and
gamma-rays from surrounding rock• Water shield also serves as a Cherenkov veto• Augmented with a muon tracker: scintillator or RPCs• Combined efficiency of Cherenkov and tracker > 99.5%
2 m ofwater
Neutron background vs thickness of water
Fast
neutr
ons
per
day
water thickness (m)
0.05
0.10
0.15
0.20
0.25
0.30
0. 1. 2.
50-ton crane
Electronic Hut Electronic Hut
Cart for moving detector module
pure water
ports for calibration
frame also serves as cable trays
Conceptual design of a underground water pool-based experimental hall
tunnel
Active Water Shield and Muon Tracker
• Specifications– High efficiency muon tracker; less than 0.3% inefficiency when
combined with the muon water Cherenkov – Good (ns) timing resolution to reduce accidentals due to ambient
radioactivity background– Muon tracker can be deployed in water pool – Robust, good long-term stability
PMT's for water Cherenkov
Moving Detectorsin Horizontal
Tunnels
Aircraft Pushback Tractors are Ideal
• Zero emission vehicles available
• Low-speed towing
• Forward and reverse towing
• Vehicle ballasted
• OK for incline (<8%)
Prototype setup at IHEP
LED
Cables
Flange to put Source Purposes: Test reflection, energy resolution, LS performance …
• Inner acrylic vessel: 1m in diameter and 1m tall, filled with normal liquid scintillator(70% mineral oil + 30% mesitylene).
• Outer stainless steel vessel: 2m in diameter and 2m tall, filled with mineral oil. PMTs mounted and immerged in oil.
• 45 MACRO PMT, 15 PMT/Ring
Attenuation Length and Light Yield
Lattn = 8.5+/-0.3m
PMTXP2020
PMTGlassTube
SourceCs137 orSr90
Liquid Scint.Or AnCrystal
61% relative to Anthracene
Very PreliminaryResolution: 15.5%@0.662MeV
Backgrounds
~350 m
~97 m
~98 m~210 m
Cosmic-ray Muon• Apply modified Gaisser parametrization for cosmic-ray flux at surface• Use MUSIC and mountain profile to estimate muon flux & energy
DYB LA Mid Far
Elevation (m) 97 98 208 347
Flux (Hz/m2) 1.2 0.73 0.17 0.045
Mean Energy (G
eV)
55 60 97 136
Summary of Background
Near Site Far Site
Radioactivity (Hz) <50 <50
Accidental B/S <0.05% <0.05%
Fast neutron background B/S 0.15% 0.1%8He/9Li B/S 0.41% ± 0.18% 0.02% ± 0.08%
• Use a modified Palo Verde-Geant3-based MC to model
response of detector:
(neutrino signal rate 560/day 80/day)
Further rejection of background may be possible by cuttingshowering muons.
Detector-related Uncertainties
Baseline: currently achievable relative uncertainty without R&D Goal: expected relative uncertainty after R&D
Absolutemeasurement
Relativemeasurement
→ 0→ 0.006
→ 0.06%
w/Swapping
→ 0
Swapping: can reduce relative uncertainty further
Summary of Systematic Errors• Reactor-related systematic errors are:
0.09% (4 cores)0.13% (6 cores)
• Relative detector systematic errors are:
0.36% (baseline)0.12% (goal)0.06% (with swapping)
• These are input to sensitivity calculations
90% confidence level90% confidence level
2 n
ear +
far (3
years)
near (4
0t) +
mid
(40 t)
1 year
Near-mid
Use rate and spectral shapeUse rate and spectral shape
Sensitivity of Daya Bay in sin2213
Daya Baynear hall
(40 t)
Tunnel entrance
Ling Aonear hall
(40 t)
Far hall(80 t)
Synergy Between Reactor and Accelerator Experiments
Before 2011: Daya Bay provides basis for early decision on future program beyond NOA for CP and mass hierarchy
After 2011: Daya Bay will complement NOA and T2K for resolving 23, mass hierarchy, and CP phase
Overall Project Schedule
Summary• The Daya Bay nuclear power facility in China and the mount
ainous topology in the vicinity offer an excellent opportunity for carrying out a reactor neutrino program using horizontal tunnels.
• The Daya Bay experiment has excellent potential to reach a sensitivity of 0.01 for sin2213.
• The Daya Bay Collaboration continues to grow.
• Will complete detailed design of detectors, tunnels and underground facilities in 2006.
• Plan to commission the Fast Deployment scheme in 2009, and Full Operation in 2010.
The Daya Bay Collaboration: China-Russia-U.S.
X. Guo, N. Wang, R. WangBeijing Normal University, Beijing
L. Hou, B. Xing, Z. ZhouChina Institute of Atomic Energy, Beijing
M.C. Chu, W.K. NgaiChinese University of Hong Kong, Hong Kong
J. Cao, H. Chen, J. Fu, J. Li, X. Li, Y. Lu, Y. Ma, X. Meng, R. Wang, Y. Wang, Z. Wang, Z. Xing, C. Yang, Z. Yao, J. Zhang, Z. Zhang, H. Zhuang, M. Guan, J. Liu, H. Lu, Y. Sun, Z. Wang, L. Wen, L. Zhan, W. ZhongInstitute of High Energy Physics, Beijing
X. Li, Y. Xu, S. JiangNankai University, Tianjin
Y. Chen, H. Niu, L. NiuShenzhen University, Shenzhen
S. Chen, G. Gong, B. Shao, M. Zhong, H. Gong, L. Liang, T. XueTsinghua University, Beijing
K.S. Cheng, J.K.C. Leung, C.S.J. Pun, T. Kwok, R.H.M. Tsang, H.H.C. WongUniversity of Hong Kong, Hong Kong
Z. Li, C. ZhouZhongshan University, Guangzhoz
Yu. Gornushkin, R. Leitner, I. Nemchenok, A. Olchevski
Joint Institute of Nuclear Research, Dubna, Russia
V.N. Vyrodov
Kurchatov Institute, Moscow, Russia
B.Y. Hsiung
National Taiwan University, Taipei
M. Bishai, M. Diwan, D. Jaffe, J. Frank, R.L. Hahn, S. Kettell, L. Littenberg, K. Li, B. Viren, M. Yeh
Brookhaven National Laboratory, Upton, New York, U.S.
R.D. McKeown, C. Mauger, C. Jillings
California Institute of Technology, Pasadena, California, U.S.
K. Whisnant, B.L. Young
Iowa State University, Ames, Iowa, U.S.
W.R. Edwards, K. Heeger, K.B. Luk
University of California and Lawrence Berkeley National Laboratory, Berkeley, California, U.S.
V. Ghazikhanian, H.Z. Huang, S. Trentalange, C. Whitten Jr.
University of California, Los Angeles, California, U.S.
M. Ispiryan, K. Lau, B.W. Mayes, L. Pinsky, G. Xu,
L. Lebanowski
University of Houston, Houston, Texas, U.S.
J.C. PengUniversity of Illinois, Urbana-Champaign, Illinois, U.S.
20 institutions, 89 collaborators
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