First Measurement of sin2 13 at Daya Bay - 東京大学 · 2012-03-29 7 . Daya Bay Experiment...
Transcript of First Measurement of sin2 13 at Daya Bay - 東京大学 · 2012-03-29 7 . Daya Bay Experiment...
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First Measurement of
sin2213 at Daya Bay
References
Result: arXiv:1203.1669
Detector: arXiv:1202.6181
Proposal: hep-ex/0701029
Shaomin CHEN, Tsinghua Univerisity
On behave of the Day Collaboration
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Outline
Overview of 13: from theories to
experiments
Daya Bay Experiment
Data analysis
Determination of sin22 13
Summary and outlook
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Overview of 13: from
theories to experiments
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Model Predications for 13
arXiv:0911.2437
Up to 2009, more than 86 models for 13 predications.
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Lepton flavor models GUT models
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Hints of 130 from Global Fits M. Huang et. al., arXiv:1111.3175
T. Schwetz et. al., arXiv:1108.1376
M C. Gonzalez-Garciaet. al., arXiv:1001.4524
F. L. Fogli et. al., arXiv:1106.6028
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Hints of 130 from Experiments
Title highlights
Chooz(2003): Search…
T2K(2011): Indication…
MINOS(2011): Improved Search…
DC(2011): Indication…
No result >2.5σ from θ13 = 0
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Meeting brief for the 250th Xiangshan (Fragrant Hill Hotel )
Scientific Meeting (2005)
… 2. Neutrino mixing angle θ13 is one of the fundamental
parameters in nature,…a key issue to be resolved. 3.…have mature technology and get strong support from Daya
Bay Nuclear Power Plant. … get preparations … to complete
this experiment. 4. International competition in determining θ13 is very
vigorous,…getting the project approved promptly is a key to
win the competition.
Initiate DayaBay Project in China
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Daya Bay Experiment
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Daya Bay Power Plant Complex
Three-pair reactor cores: 2.9 6=17.4GWth
Each core produces 6 1020 anti-e’s/s
Mountains near by
55 km
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Reactor Anti-e oscillation
2 2 2 2 2 2 2 2
12 13 31 12 13
4 2 2 2
13 12 21
3
2 2 2
2 2 31 21 3
2
1
13 12
cos sin 2 sin (1.267 ) sin sin 2 s
1.
in (1.2
267( ) 1.2671sin 2 sin [cos cos ]
2 2 2
cos sin 2 sin (1.2
( )
)1
7
6
)
7
6
e e
L L
m
P
Lm
E
m L m L
E E
m mE E
Approximated to
Survival probability:
4 2 2 2 2 2
13 3
2
13 12 221cos sin 2 sin (1.2 sin 2 sin (67 ) 1.26
)
1 7
(
)
e e
L
Em
P
mL
E
Well measured by KamLAND
Well measured by MINOS, SK
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How to Measure sin2213?
Near
detectors
constrain
flux
Far detectors
measure
oscillation
Far/near
νe counts
Detector
Target Masses
Base lines
Detector
efficiencies
Oscillation
deficit
Use relative measurement
Avoid large uncertainty
from predicted reactor flux
First proposed by L. A.
Mikaelyan and V.V. Sinev,
PAN 63 1002 (2000)
Key inputs
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Baseline Selection
4 2 2
2 2 2
13 3
2
13 12
2
21cos sin 2 sin (1.2
sin 2 sin (
67 )
1.26
)
1
7
(
)
e e
L
E
m
P
m
L
E
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Experimental Layout
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Neutrino Detection at DayaBay
0
0
n
n Gd
Reacti on:
Prompt signal:
Delayed sign
2 '
'
p
( >2 =1.022MeV)
Gd ( ~ 8MeV, ~ 28 )
d
al:
Delay ( 2.2MeV,ed sig ~ 180 )n:
pnal
e
eeE m
E s
E s
s
s
e
e e
Neutrino energy:
n n p( )e e
E T T M M m
Threshold=1.8 MeV
Antineutrino Interaction Rate (events/day per AD module, 100%eff.)
Daya Bay near site 960
Ling Ao near site 760
Far site 90
No Oscillation 2012-03-29 14
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Signature of an IBD Signal
Cannot “see” at Daya Bay
LS+Gd zone: e+ + n (n/Gd + n/H)
LS zone: e+ + n (n/Gd + n/H)
Uniform scintillation light
6 1020 e’s/s/core
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Anti-neutrino Detector
Three zones modular structure: Target: 20t, 1.6m Gd-loaded scintillator
-catcher: 20t, 45cm normal scintillator
Buffer shielding: 40t, 45cm oil
Reflector at top and bottom
192 8”PMT/module
PMT coverage: 12%(with reflector)
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Automatic Calibration Unit
Three Z axis: – Center, edge, -catcher
Each axis with 3 sources: – LED
• t0, gain and relative QE
– 68Ge (20.511 MeV ’s)
• Threshold & non-linearity…
– 241Am-13C + 60Co (1.17+1.33 MeV ’s)
• Neutron capture time, …
• Energy scale, response function, …
Once per week
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Muon Veto Detector
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FEE and Trigger System
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Clock System
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Data Acquisition System
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Antineutrino Detector Assembly
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Detector Filling Gd-LS MO LS
Detectors are filled from same reservoirs “in-pairs” within < 2 weeks.
Target mass determination error ± 3kg out of 20,000 <0.03% during data taking period
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Detector Deployment
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Radioactivity Background Shielding
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Trigger performance
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Spectrum for all AD triggers
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Before veto After veto
AD1 AD2 AD3 AD4 AD5 AD6
~285 ~270 ~230 ~180 ~150 ~150
Trigger
threshold
0.4 MeV Hz
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Unexpected PMT Feature
Flashers Neutrinos
Inefficiency to neutrinos: 0.024% 0.006%(stat) Contamination: < 0.01%
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Unexpected Bkg from ACU
241Am-13C leakage
Uncorrelated: 230evts/day/AD
Correlated: 0.2evts/day/AD 2012-03-29 29
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Detector live days
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Current Oscillation Analysis:
- Dec. 24, 2011 – Feb. 17, 2012
- All 3 halls (6 ADs) operating
- DAQ uptime: >97%
- Antineutrino data: ~89%
Two Detector Comparison:
- Sep. 23, 2011 – Dec. 23, 2011
- Side-by-side comparison
- Demonstrated detector systematics
better than requirements.
- Details presented in:
arXiv:1202.6181 (2012)
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Data Analysis
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Blind Analysis
Parameter Set uncertainty Actual precision
Target mass 0.5% 0.1%
Base line 5m 30cm
Reactor flux 10% 0.13%
Nominal values initially assigned with large uncertainties.
Precise values provided when all the analyses are finalized
and frozen.
Motivation: Conceal the true value of sin2213
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Background Classification
Multiplicity
+ e/n
Accidentals
2 ’s
Fast neutrons
+ n
8He/9Li
+n
Am-C
2 ’s
13C(,n)16O
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Multiplicity Cuts
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Multiplicity cut Efficiency = e1 e2 e3
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Accidental Background
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Fast Neutron Background
Background estimate:
extrapolation method
Prompt: n collides/stops in target
Delayed: n/Gd
n
Cosmic ray muon
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8He/9Li Background
e-
n
Cosmic ray muon
(8He/9Li )
= 171.7ms/257.2ms
Background estimate:
fit with known (8He/9Li) 2012-03-29 37
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Selection Criteria
Pre-selection
– No flasher + no trigger (-2 μs, 200 μs) to a WP
muon
Neutrino event selection
– Multiplicity cuts
• (tn-Te) < 200 μs
• No triggers before e+ and after n
– Muon veto cuts
• 1s after an AD shower muon
• 1ms after an AD muon
• 0.6ms after a WP muon 2012-03-29 38
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IBD Events
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IBD Reaction Positions
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IBD Candidates at Each Hall
EH1
57,910 signal
candidates
EH2
22,466 signal
candidates
10,416 signal
candidates
EH3
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Data Set Summary AD1 AD2 AD3 AD4 AD5 AD6
Antineutrino
candidates 28935 28975 22466 3528 3436 3452
DAQ live time
(day) 49.5530 49.4971 48.9473
Efficiency 0.8019 0.7989 0.8363 0.9547 0.9543 0.9538
Accidentals
(/day) 9.82
±0.06
9.88
±0.06
7.67
±0.05
3.29
±0.03
3.33
±0.03
3.12
±0.03
Fast neutron
(/day) 0.84
±0.28
0.84
±0.28
0.74
±0.44
0.04
±0.04
0.04
±0.04
0.04
±0.04
8He/9Li (/day) 3.1±1.6 1.8±1.1 0.16±0.11
Am-C corr. (/day) 0.2±0.2
13C(α, n)16O
(/day) 0.04
±0.02
0.04
±0.02
0.035
±0.02
0.03
±0.02
0.03
±0.02
0.03
±0.02
Antineutrino
rate (/day) 714.17
±4.58
717.86
±4.60
532.29
±3.82
71.78
±1.29
69.80
±1.28
70.39
±1.28 2012-03-29 42
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Determination of
sin22 13
Far/near
νe counts
Detector
Target Masses
Base lines
Detector
efficiencies
Oscillation
deficit 2012-03-29 43
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Distances from Reactors to ADs
Detailed Survey
- GPS above ground
- Total Station underground
- Final precision: 28mm
Validation
- Three independent
calculations
- Cross-check survey
- Consistent with reactor
plant and design plans
GPS-based Total Station
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Target Mass
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Target Mass = total mass – overflow mass
Overflow Mass
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Reactor Antineutrino Flux
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Isotope fission rates vs. reactor burnup
Reactor operators provide: • Thermal power data: Wth
• Relative isotope fission fract.: fi
Energy released/fission: ei V. Kopekin et al., PAN 67, 1892 (2004)
Anti-e spectra/fission: Si(Eν) P. Huber, PRC84, 024617 (2011)
T. Mueller et al., PRC83, 054615 (2011)
A. A. Hahn et al., PLB218, 365 (1989)
P. Vogel et al., PRC24, 1543 (1981)
K. Schreckenbach et al., PLB160, 325 (1985)
Flux estimated using:
Flux model has negligible impact on
far vs. near oscillation measurement
( ) ( / ) ( )( / )
istopes
thi i
ii ii
WS E f F S E
f F e
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Antineutrino Rate vs. Time
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Detected rate strongly
correlated with reactor
flux expectations.
Predicted Rate:
• Assume no oscillation.
• Normalization is
determined by fit to data.
• Absolute normalization
is within a few percent
of expectations.
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Uncertainty Summary
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For near/far oscillation,
only uncorrelated
uncertainties are used.
Largest systematics are
smaller than far site
statistics (~1%)
Influence of uncorrelated
reactor systematics
reduced by far vs. near
measurement.
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Far/Near Ratio
6
4f
6
n1 2 3
4
[ ( ) ]
i
i
i i
i
MN
RN
M M M
Mi : measured antineutrino rates
αi, βi : determined from base lines
and reactor fluxes.
R = 0.940 ± 0.011 (stat) ± 0.004 (syst)
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sin2213 Measurement
sin22θ13
= 0.092
± 0.016 (stat)
± 0.005 (syst)
sin22θ13 = 0
excluded at
5.2σ
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Asymmetric CI in 13
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Where Are We Now?
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Daya Bay Goal for 3 years
3/29/2012
Observation of Electron-antineutrino Disappearance
53
Assume: m231 = 2.43 10-3 eV2
Rel. detector syst. = 0.38%
We are here
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The Daya Bay Collaboration Europe (2)
JINR, Dubna, Russia
Charles University, Czech Republic
North America (16) LBNL, BNL, Caltech, Iowa State Univ.,
Illinois Inst. Tech., Princeton, RPI,
Siena, UC-Berkeley, UCLA,
Univ. of Cincinnati, Univ. of Houston,
Univ. of Wisconsin-Madison,
Univ. of Illinois-Urbana-Champaign,
Virginia Tech., William & Mary
Asia (20) IHEP, Beijing Normal Univ., Chengdu Univ.
of Sci. and Tech., CGNPG, CIAE, Dongguan
Univ.Tech., 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. ~230 Collaborators
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Roadmap of Daya Bay
2005.04: Got green light at 250th Xiangshan Meeting
2006.10:Passed DOE scientific review
2007.01:CDR released (hep-ex/0701029)
2007.10: Ground breaking ceremony
2009.07: Planed to deploy first detector
2011.08.15: EH1 started operation
2010.09: Planed to take data with final configuration
2011.11.05: EH2 started data taking
2011.12.24: Took data with 2-1-3 configuration
2012.06: Expected with final configuration
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Summary and Outlook
An unambiguous observation of electron-
antineutrino disappearance at Daya Bay
Interpretation of disappearance as neutrino
oscillation yields:
ruling out zero at 5.2 standard deviations.
More statistics expected before this June
Installation of final pair of ADs this summer
R = 0.940 ± 0.011 (stat) ± 0.004 (syst)
sin22θ13 = 0.092± 0.016 (stat)± 0.005 (syst)
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