First Measurement of2sin 213 at Daya Bay

Shaomin CHEN, Tsinghua Univerisity
On behave of the Day Collaboration

2012-03-29

References
Result: arXiv:1203.1669
Detector: arXiv:1202.6181
1
Proposal: hep-ex/0701029

Outline Overview of 13: from theories toexperiments
 Daya Bay Experiment
 Data analysis
 Determination of sin22 13
 Summary and outlook

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Overview of 13: fromtheories to experiments

2012-03-293Model Predications for 13
Lepton flavor models

GUT models

Up to 2009, more than 86 models for 13 predications.
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4arXiv:0911.2437

Hints of 130 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 130 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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Initiate DayaBay Project in China
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 towin the competition.

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Daya Bay Experiment2012-03-29

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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 by55 km
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9Reactor Anti-e oscillation
Survival probability:P ( e   e )L)
ELL2
 cos 2 12 sin 2 213 sin 2 (1.267  m31 )  sin 2 12 sin 2 213 sin 2 (1.267  m322  )E
E22
1.267( m31 m21)L
1.267m321 L
1 22
 sin 213 sin 12 [cos cos]
22E2E2 1  cos4 13 sin 2 212 sin 2 (1.267  m21

Approximated toWell measured by MINOS, SKP ( e   e )21  cos4 13 sin 2 212 sin 2 (1.267  m21LL)  sin 2 213 sin 2 (1.267  m322  )EEWell measured by KamLAND
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How to Measure sin2213?
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

Near
detectors
constrainflux

Far detectors
measureoscillation

Detector
efficiencies

Oscillation
11deficit

Base lines

Far/near
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νe counts

Detector
Target MassesBaseline SelectionP ( e   e )21  cos 4 13 sin 2 212 sin 2 (1.267  m21

 sin 2 213 sin 2 (1.267  m322 

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EL)
E

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Experimental Layout

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Neutrino Detection at DayaBayReaction:  e  p  e  n
Prompt signal: e  e  2 ' s(Ee >2me =1.022MeV)

Delayed signal: n  Gd  Gd   ' s ( E ~ 8MeV,  0 ~ 28 s)
Delayed signal: n  p  d  ( E  2.2MeV,  0 ~ 180 s)

Neutrino energy:

Threshold=1.8 MeVE  Te  Tn  (M n  M p )  me
Antineutrino Interaction Rate(events/day per AD module, 100%eff.)

Daya Bay near site
Ling Ao near site
Far site
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960
760
90
No Oscillation

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Signature of an IBD Signal
Cannot “see” at Daya Bay

6  1020 e’s/s/core

LS+Gd zone: e+ + n (n/Gd + n/H)
LS zone: e+ + n (n/Gd + n/H)
Uniform scintillation light2012-03-29

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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 (20.511 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
LSGd-LS

MODetectors are filled fromsame reservoirs “inpairs” within < 2 weeks.
Target mass
determination error ±3kg out of 20,000<0.03% during datataking 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

Before  vetoTriggerthreshold
0.4 MeV2012-03-29

After  veto

AD1 AD2 AD3 AD4 AD5 AD6~285 ~270 ~230 ~180 ~150 ~150 Hz
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Unexpected PMT Feature
Inefficiency to neutrinos:
0.024%  0.006%(stat)
Contamination: < 0.01%
Neutrinos

2012-03-29

Flashers

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Unexpected Bkg from ACU

 241Am-13C leakage
Uncorrelated: 230evts/day/AD
Correlated: 0.2evts/day/AD
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Detector live days
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)2012-03-29

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Data Analysis

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Blind Analysis
Motivation: Conceal the true value of sin2213
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 finalizedand frozen.

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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

Multiplicity cut Efficiency = e1  e2  e3
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Accidental Background2012-03-29

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Fast Neutron BackgroundCosmic ray muonn  Prompt: n collides/stops in target
Delayed:n/Gd
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Background estimate:extrapolation method36

8He/9Li BackgroundCosmic ray muon

ne-  (8He/9Li )= 171.7ms/257.2ms

Background estimate:2012-03-29
fit with known (8He/9Li)

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Selection Criteria
Pre-selection– No flasher + no trigger (-2 μs, 200 μs) to a WPmuon

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
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IBD Events

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IBD Reaction Positions

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IBD Candidates at Each Hall
EH1

EH257,910 signal
candidates

22,466 signal
candidates

EH3

10,416 signal
candidates

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Data Set Summary
Antineutrino
candidates

DAQ live time(day)

AD1

AD2

AD3

AD4

AD5

AD6

28935

28975

22466

3528

3436

3452

49.5530

49.497148.9473

Efficiency

0.80190.79890.83630.95470.95430.9538

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

Am-C corr. (/day)13C(α, n)16O

1.8±1.1

0.16±0.11

0.2±0.2(/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
42

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Determination of
sin22 13
Base lines

Far/near
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νe counts

Detector
Target Masses

Detector
efficiencies

Oscillation
43
deficitDistances from Reactors to ADs
Detailed Survey- GPS above ground- Total Station underground- Final precision: 28mmValidation

Total Station

GPS-based- Three independentcalculations- Cross-check survey- Consistent with reactor
plant and design plans

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Target Mass
Overflow Mass

Target Mass = total mass – overflow mass

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Reactor Antineutrino Flux
Flux estimated using:

Isotope fission rates vs. reactor burnup

istopesWth
S ( E ) ( fi / F ) Si ( E )i ( fi / F )ei i

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)
Flux model has negligible impact on
A. A. Hahn et al., PLB218, 365 (1989)
far vs. near oscillation measurement
P. Vogel et al., PRC24, 1543 (1981)
K. Schreckenbach et al., PLB160, 325 (1985)
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Antineutrino Rate vs. Time Detected rate strongly
correlated with reactor
flux expectations.
 Predicted Rate:• Assume no oscillation.
• Normalization isdetermined by fit to data.
• Absolute normalization
is within a few percent
of expectations.

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Uncertainty Summary
For near/far oscillation,
only uncorrelated
uncertainties are used.

Largest systematics aresmaller than far sitestatistics (~1%)

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Influence of uncorrelated
reactor systematics
reduced by far vs. nearmeasurement.
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Far/Near Ratio
6NfR
NnMi 4i6

 [ ( M  M )   M ]i 4i

12i

3

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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sin2213 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
We arehere
Assume: m231 = 2.43  10-3 eV2Rel. detector syst. = 0.38%

Observation of Electron-antineutrino Disappearance
3/29/201253

The Daya Bay Collaboration
Europe (2)JINR, Dubna, Russia
Charles University, Czech Republic

North America (16)Asia (20)

LBNL, BNL, Caltech, Iowa State Univ., IHEP, Beijing Normal Univ., Chengdu Univ.
of Sci. and Tech., CGNPG, CIAE, Dongguan
Illinois Inst. Tech., Princeton, RPI,Univ.Tech., Nanjing Univ., Nankai Univ.,
Siena, UC-Berkeley, UCLA,NCEPU, Shandong Univ.,
Univ. of Cincinnati, Univ. of Houston,
Shanghai Jiao tong Univ., Shenzhen Univ.,
Univ. of Wisconsin-Madison,
Tsinghua Univ., USTC, Zhongshan Univ.,
Univ. of Illinois-Urbana-Champaign,Virginia Tech., William & Mary Univ. of Hong Kong, Chinese Univ. of Hong Kong,
National Taiwan Univ., National Chiao Tung~230 Collaborators
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Univ., National United Univ. 54

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 electronantineutrino disappearance at Daya Bay
R = 0.940 ± 0.011 (stat) ± 0.004 (syst)
 Interpretation of disappearance as neutrino
oscillation yields:
sin22θ13 = 0.092± 0.016 (stat)± 0.005 (syst)
ruling out zero at 5.2 standard deviations.
 More statistics expected before this June Installation of final pair of ADs this summer

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