1. Current Results from Reactor Neutrino Experiments
Soo-Bong Kim (KNRC, Seoul National University)
“Tsukuba Global Science Week (TGSW2016), Tsukuba, Sep , 2016”

2. Neutrino Mixing Angles
SNO, Super-K;
KamLAND
Solar Neutrino Oscillation
Atmospheric Neutrino Oscillation
Reactor Neutrino Oscillation
q12
q23
q13
9o (2012)
Daya Bay, RENO
Double Chooz
~45o (1998)
Super-K; K2K
2015
Nobel
Prize
“Neutrino has mass”
“Established three-flavor mixing framework”

3. Neutrino Physics with Reactor
1956 Discovery of (anti)neutrino
Savannah River
2003 Observation of reactor neutrino oscillation (q12 & Dm212)
KamLAND
2012 Measurement of the smallest mixing angle q13

4. Reactor Neutrinos
Reactor Neutrinos
Nuclear Power Plants
~5×1020 n/sec
Hanbit
Cost-free, intense, low-energy & well-known neutrino source !

5. Reactor 13 Experiments RENO at Yonggwang, Korea
Daya Bay at Daya Bay, China
Double Chooz at Chooz, France

6. q13 Reactor Neutrino DetectorsMO LS
H2O
Gd-LS

7. Comparisons of Reactor 13 Experiments
Baselines
RENO DB DC

8. First q13 measurements in 2012
~ 4 years ago
Double Chooz
Daya Bay
RENO
Publication
PRL 108,
(Mar. 30, 2012)
PRL 108,
(Apr.27, 2012)
PRL 108,
(May 11, 2012)
sin2(2θ13)
0.086
0.092
0.113
Stat. error
0.041
(101 days)
0.016
(49 days)
0.013
(220 days)
Syst. error
0.030
(flux uncert.)
0.005
(MC driven)
0.019
(data driven)
Significance
1.7 σ
5.2 σ
4.9 σ
1 month
2 weeks

9. RENO Collaboration Reactor Experiment for Neutrino Oscillation
(8 institutions and 40 physicists)
Chonnam National University
Dongshin University
GIST
Gyeongsang National University
Kyungpook National University
Seoul National University
Seoyeong University
Sungkyunkwan University
Total cost : $10M
Start of project : 2006
The first experiment running with both near & far detectors from Aug. 2011
YongGwang (靈光) :

10. RENO Experimental Set-up
Far Detector
Near Detector
1380m
290m
120 m.w.e.
450 m.w.e.

11. RENO Detector Target : 16.5 ton Gd-LS (R=1.4m, H=3.2m)
Gamma Catcher : 30 ton LS (R=2.0m, H=4.4m)
Buffer : 65 ton mineral oil (R=2.7m, H=5.8m)
Veto : 350 ton water (R=4.2m, H=8.8m)
354 ID 10” PMTs
67 OD 10” PMTs

12. Detection of Reactor Antineutrinos
(prompt signal)
(delayed signal)
~180 ms
+ p  D + g (2.2 MeV)
~28 ms
(0.1% Gd)
+ Gd  Gd + g‘s (8 MeV)
Neutrino energy measurement

13. Coincidence of prompt and delayed signals
(prompt signal)
(delayed signal)
Delayed signal
Prompt signal
n-Gd IBD
~30 ms
8 MeV
~200 ms
n-H IBD
2.2 MeV

14. Backgrounds 9Li m m m g p n n e Gd Gd n Gd
Accidental coincidence between prompt and delayed signals
Fast neutrons produced by muons, from surrounding rocks and inside detector (n scattering : prompt, n capture : delayed)
9Li/8He b-n followers produced by cosmic muon spallation
Accidentals
Fast neutrons
9Li/8He b-n followers m m m g p n n
9Li e Gd Gd n Gd

15. New Results from RENO
Observation of energy dependent disappearance of reactor neutrinos to measure Dmee2 and q13 using ~500 days of data (Aug ~ Jan. 2013)
“Observation of Energy and Baseline Dependent Reactor Antineutrino Disappearance in the RENO Experiment” (PRL 116, , 2016)
- PRD to be submitted soon for details
Measurement of absolute reactor neutrino flux
Observation of an excess at ~5 MeV in reactor neutrino spectrum using ~1400 days of data
Independent measurement of q13 with n-H for a delayed signal (additional background reduction achieved)
Obtained results from a sterile neutrinos search

16. RENO Data-taking Status
Data taking began on Aug. 1, 2011 with both near and far detectors.
(DAQ efficiency : ~95%) A B C D
A (220 days) : First q13 result
[11 Aug, 2011~26 Mar, 2012]
PRL 108, (2012)
Now
B (403 days) : Improved q13 result
[11 Aug, 2011~13 Oct, 2012]
NuTel 2013, TAUP 2013, WIN 2013
Total ~ 1700 days

17. Delayed Signals from Neutron Capture by Gd

18. Measured Spectra of IBD Prompt Signal
Near Live time = days
# of IBD candidate = 290,775
# of background = 8,041 (2.8 %)
Far Live time = days
# of IBD candidate = 31,541
# of background = (4.9 %)

19. New q13 Measurement by Rate-only Analysis
new result
By minimizing
PRL 116, (2016)

20. In 2014, RENO showed the 5 MeV excess
The 5 MeV Excess is there !
RENO
Double Chooz
Daya Bay
In 2014, RENO showed the 5 MeV excess
comes from reactors.
Seon-Hee Seo, SNU
Hawaii 2014

21. Observation of an excess at 5 MeV
1400 days of data (Aug – Sep 2015)
(Preliminary)
The measured near spectrum is compared with prediction using χ2-square test.
Fraction of 5 MeV excess: ± 0.27 (%)
~3%
Significance of the 5 MeV excess: ~9σ
~2.5%

22. Correlation of 5 MeV Excess with Reactor Power
1400 days of data
5 MeV excess
has a clear
correlation
with reactor
thermal power !
two or three reactors are off
All the six reactors are on
The 5 MeV excess comes from reactors!

23. Correlation of 5 MeV excess with 235U isotope fraction
(Preliminary)
235U fraction corresponds to freshness of reactor fuel
Fit function χ2
y = p0
1.407
y = p0 + p1*x
0.233
Δχ2 = 1.174
P-value = 0.240
(End
of reactor cycle)
(Beginning
of reactor cycle)

24. Measurement of Absolute Reactor Neutrino Flux
R (data/prediction) = ± (500 days)
The flux prediction is with Huber + Mueller model
Flux weighted baseline at near : 411 m
*Prediction is corrected for three flavor neutrino oscillation
Preliminary
Daya Bay
Deficit of observed reactor neutrino fluxes relative to the prediction (Huber + Mueller model) indicates an overestimated flux or possible oscillation to sterile neutrinos

25. Reactor Neutrino Oscillations
Probability νe
1.0
flux before oscillation observed here
Oscillations observed as a deficit of anti-neutrinos
sin22θ13
the position of the minimum is defined by Δm2ee
Distance
1200 to 1800 meters
cos 2 𝜃 12 Δ 𝑚2 21

26. Energy Calibration from g-ray Sources
Non-linear resonse of the scintillation energy is calibrated using γ-ray sources.
The visible energy from γ-ray is corrected to its corresponding positron energy.
Fit function : Evis/Etrue = a – b/(1 – exp(-cEtrue – d))

27. Far/Near Shape Analysis for |Dmee2|
PRL 116, , 2016
Minimize Χ2 Function

28. Results from Spectral Fit
Rate+shape
new results
(± 12 %)
(± 10 %)

29. Observed L/E Dependent Oscillation

30. q13 & |Dm2ee| in Daya Bay
Neutrino 2016
1230 days data

31. q13: Double Chooz 468 days JHEP 10 (2014) 086 Assuming Dm231 =
 MINOS result

32. Summary: Latest n-Gd Results
Rate + Shape [χ2/NDF ]
sin22θ13
± Total Error
|Δmee|2 (×103 eV2)
RENO [58.9 / 66 ]
0.082 ± 0.010
2.62
Daya Bay [134.6/146]
0.084 ± 0.003
2.50 ± 0.08
Double Chooz [52.2/40]
0.09 -
+0.24
- 0.26
+0.032

33. Future Prospects on q13 Double Chooz RENO Daya Bay Data 3 yrs Near&Far
Δ(sin2(2θ13))
~10 %
~5 %
~3 %
Δ(|m2ee|) - J.
FroST

34. n-H IBD Event Vertex Distribution
n-H IBD Analysis|
Motivation:
1. Independent measurement of q13 value.
2. Consistency and systematic check on reactor neutrinos.
n-H IBD Event Vertex Distribution
target
g-catcher
Seon-Hee Seo, SNU

35. Delayed Spectrum and Capture Time|
Delayed signal peak:
~2.2 MeV
Mean coincidence time:
~ 200 ms 35

36. q13 Measurement with n-H
(Preliminary, 500 days)

37. Light Sterile Neutrino Search Results
(Preliminary)
All 500 days of RENO data
Consistent with standard 3-flavor
neutrino oscillation model
Able to set stringent limits in
the region
eV2
full curves assumes

38. Summary
Observation of energy dependent disappearance of reactor neutrinos and our first measurement of Dmee2
12 % precision
10 % precision
Measured absolute reactor neutrino flux : R= 0.946±0.021
Observed an excess at 5 MeV in reactor neutrino spectrum
Measurement of q13 using n-H IBD analysis : 0.086±0.019
Obtained an excluded region from a sterile neutrino search
sin(2q13) to 5% accuracy
Dmee2 to 0.15×10-3 eV2 (5%) accuracy for final sensitivity

39. Thanks for your attention!