1 the daya bay reactor electron anti-neutrino oscillation experiment jianglai liu (for the daya bay...
TRANSCRIPT
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The Daya Bay Reactor Electron Anti-neutrino Oscillation Experiment
Jianglai Liu (for the Daya Bay Collaboration) California Institute of Technology
APS DNP Conference, Newport News, Oct. 13, 2007
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Physics Motivation
Weak eigenstate mass eigenstate Pontecorvo-Maki-Nakagawa-Sakata Matrix
3
2
1
3
2
1
321
321
321
7.06.04.0
7.06.04.0
?5.08.0
UUU
UUU
UUU eeee
100
00
00
cossin0
sincos0
001
cos0sin
010
sin0cos
100
0cossin
0sincos2
1
2323
2323
1213
1313
1212
1212
i
i
i
i
e
e
e
e
Parametrize the PMNS matrix as:
Solar, reactor reactor and accelerator 0Atmospheric, accelerator
23 ~ 45° 12 = ~ 32° 13 = ?
13 is the gateway of CP violation in lepton sector!
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Measuring 13 Using Reactor Anti-neutrinos
E
Lm
E
LmPee 4
sin2sincos4
sin2sin12
21212
213
42
13213
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Electron anti-neutrino survival probability
e disappearance at short baseline(~2 km): unambiguous measurement of 13
Large oscillation >50 km; negligible <2 km
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Increase statistics: Use powerful reactors & large target mass & optimized baselineSuppress background:
Go deeper underground
High performance veto detector to MEASURE the background
Reduce systematic uncertainties:Reactor-related: Utilize near and far detectors to minimize reactor-related errors
Detector-related:
Use “Identical” pairs of detectors to do relative measurement
Comprehensive program in calibration/monitoring of detectors
Previous best experimental limits from Chooz: sin2(213) <0.17 (m2
31=2.510-3 eV, 90% c.f.)
Daya Bay: Goal and Approach
Daya Bay:determine sin2213 with a sensitivity of 1%
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4 x 20 tons target mass at far site
Daya Bay: Powerful reactor by mountains
Far site1615 m from Ling Ao1985 m from DayaOverburden: 350 m
900 m
Daya Bay Near site363 m from Daya BayOverburden: 98 m
Ling Ao Near site~500 m from Ling AoOverburden: 112 m
465 m
295 m
810
m
22.9 GW
22.9 GW
(under construction) 22.9 GW in 2010
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Detection of e
Inverse -decay in Gd-doped liquid scintillator:
0.3b + Gd Gd* Gd + ’s(8 MeV) (t~30μs) + p D + (2.2 MeV) (t~180μs)
50,000b
nepe
Time, space and energy-tagged signal suppress background events.
Delayed Energy SignalPrompt Energy Signal
E Te+ + 1.8 MeV
1 MeV 8 MeV
6 MeV 10 MeV
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Antineutrino Detector
Cylindrical 3-Zone Structure separated by acrylic vessels:
I. Target: 0.1% Gd-loaded liquid scintillator, radius=half height= 1.55 m, 20 ton
II. -catcher: liquid scintillator, 42.5 cm thick
III. Buffer shielding: mineral oil, 48.8 cm thick
vertex
14%~ , 14cm
(MeV)
E E
11.6 %
12.5 cm for 8 MeV e-
With 192 PMT’s on circumference
and reflective reflectors on top and bottom:
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Calibrating Energy Cuts
Automated deployed radioactive sources to calibrate the detector energy and position response within the entire range.
68Ge (0 KE e+ = 20.511 MeV ’s) 252Cf (~4 neutrons/fission, 2.2 MeV n-p and 8 MeV n-Gd captures) LEDs (timing and PMT gains) R=1.35mR=0R=1.775 m
In addition, cosmogenic background (n and beta emitters) provide additional energy scale calibration sampled over the entire fiducial volume
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Muon Veto System
Surround detectors with at least 2.5m of water, which shields the external radioactivity and cosmogenic background
Water shield is divided into two optically separated regions (with reflective divider, 8” PMTs mounted at the zone boundaries), which serves as two active and independent muon tagger
Augmented with a top muon tracker: RPCs
Combined efficiency of tracker > 99.5% with error measured to better than 0.25%
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Backgrounds
DYB site LA site Far siteFast n / signal 0.1% 0.1% 0.1%9Li-8He / signal 0.3% 0.2% 0.2%
Accidental/signal <0.2% <0.2% <0.1%
Background = “prompt”+”delayed” signals that fake inverse-beta events
Three main contributors, all can be measured:
Background type Experimental Handle
Muon-induced fast neutrons (prompt recoil, delayed capture) from water or rock
>99.5% parent “water” muons tagged
~1/3 parent “rock” muons tagged9Li/8He (T1/2= 178 msec, b decay w/neutron emission, delayed capture)
Tag parent “showing” muons
Accidental prompt and delay coincidences Single rates accurately measured
B/S:
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Baseline Systematics Budget
Detector Related 0.38%
Reactor related 0.13%
Backgrounds 0.3% (Daya Bay near),
0.2% (Ling Ao near and far)
Signal statistics 0.2% (3 years of running)
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Daya Bay Sensitivity
90% confidence level, “baseline” detector uncertainties90% confidence level, “baseline” detector uncertaintiesUse rate and spectral shapeUse rate and spectral shape
Milestones DoE CD1 review, April 2007, approved Oct. 13 (Today!) Tunnel construction groundbreaking DoE CD2 review, Jan 2008 July 09 Deployment of the first pair of detectors Sept. 2010 Begin data taking with near-far
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Backup
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Detector-related
Baseline: currently achievable relative uncertainty without R&DGoal: expected relative uncertainty after R&DSwapping: can reduce relative uncertainty further