1. Search for Sterile Neutrinos
at RENO
In-Sung Yeo
May 22, 2017

2. Outline Introduction Motivation Experimental Set-up & Detector
Data-taking & Analysis
χ2 Fitting for Sterile Neutrino Search
- Rate + Shape Analysis
Results
Summary

3. Introduction
Since the past decades, great progress in the understanding of Pontecorvo-
Maki-Nakagawa-Sakata matrix has been made.
Three-neutrino mixing framework is well established, but many experiments
results cannot be explained within the standard three-flavor framework.
It seems to require an additional neutrino.
“LSND anomaly”
(The LSND experiment observed a small excess of νe events in νμ beam,
and MiniBooNE experiment see the similar size excess.)
“Gallium anomaly”
( GALEX and SAGE obtained that the ratio of the number of measured
and predicted events, R, is 0.86±0.05 )
LSND νμ→νe search
MiniBooNE νμ→νe search
Gallium anomaly
PRD 64, (2001)
PRL 110, (2013)
PRC 73, (2006)

4. -> Create additional oscillation modes
Reactor antineutrino anomaly
“Reactor antineutrino anomaly”
( R, is 0.940±0.027, ~6% deficit)
- Antineutrino flux increase
- Neutron lifetime decrease
PRD 83, (2011)
Daya Bay, Double Chooz, RENO experiments are also searching for sterile
neutrinos.
Light sterile states can be mixed with active states through the mass
eigenstates.
-> Create additional oscillation modes

5. Sterile Neutrinos Mixing
Four-neutrino mixing
The survival probability of electron antineutrinos is given by
<θ13 & θ12 oscillation terms>
<θ14 oscillation terms>

6. Motivation (reactor anomaly)
< Results of short baseline experiments >
CHOOZ Data
 6% deficit !!
KamLAND data
RENO Near
RENO Far
(θ13 oscillation)
T. Mueller et al., Phys. Rev. C 83, (2011)

7. RENO Collaboration Reactor Experiment for Neutrino Oscillation
(9 institutions and 40 physicists)
Chonnam National University
Dongshin University
GIST
Gyeongsang National University
Kyungpook National University
Sejong 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) :
(New name : Hanbit )

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

9. RENO Detector 354 ID +67 OD 10” PMTs
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

10. RENO Data-taking Status
Data taking began on Aug with both near and far detectors.
(DAQ efficiency : ~95%) A
A (220 days) : First q13 result
[11 Aug, 2011~26 Mar, 2012]
PRL 108, (2012) B
B (403 days) : Improved q13 result
[11 Aug, 2011~13 Oct, 2012]
NuTel 2013, TAUP 2013, WIN 2013
C (~500 days) : New result
Shape+rate analysis (q13 and |Dmee2|)
[11 Aug, 2011~21 Jan, 2013]
PRL 116, (2016)
→ Sterile neutrino search in progress C
1500 days
Total observed reactor neutrino events as of today (1500 days):
~ 1.5M (Near), ~ 0.15M (Far)

11. Detection of Reactor Antineutrinos
(Prompt signal)
(Delayed signal)
~200 ms
+ p  D + g (~2.2 MeV)
~30 ms
(0.1% Gd)
+ Gd  Gd + g‘s (~8 MeV)
Neutrino energy measurement
Prompt signal
10-40 KeV
1.8 MeV
Delayed signal
~8 MeV

12. 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
Good agreement with data and MC.

13. Delayed Signals from Neutron Capture by Gd

14. Backgrounds m n m n m 9Li g p e n
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 n Gd m n m
9Li g p e Gd n Gd

15. IBD Candidates & Backgrounds
Near
Far
DAQ live time
(days)
458.49
489.93
IBD candidates
290,755
31,541
Total BKG rate
(/day)
17.54± 0.83
3.14± 0.21
IBD rate (/day)
after BKG subtraction
616.67± 1.44
61.24± 0.42

16. Observed Daily Averaged IBD Rate
Good agreement with observed rate and prediction
Accurate measurement of thermal power by reactor neutrinos

17. Expected IBD Templates
<Oscillation parameter coordinate>
Inputs
IBD MC Template
Oscillation parameters
Signal MC with 4 isotopes
Interaction fraction
Expected # of IBD
Detection efficiency
Dead time
<Prompt spectrum>
<Examples>
Expected far to near ratio template
|Dm241| = 0.1 eV2
Expected far to near ratio template
sin22q14 = 0.1

18. χ2 Fitting for Sterile Neutrino Search - Rate + Shape Analysis
Oscillation parameters are determined using far/near ratio of IBD prompt energy spectrum
Minimize χ2 function
Observed far/near ratio
Expected far/near ratio
(Detection efficiency, dead time, thermal power, fission fraction, energy scale....)

19. Results of Excluded Region
500 days of RENO data
Consistent with standard 3-flavor
neutrino oscillation model
<Examples>
Exclusion
region
full curves assumes
Able to set limits in the region

20. Deviation (θ14) from θ13 Oscillated Spectrum
<Unexcluded parameters>
Normalized toθ13 oscillation
Exclusion
region

21. Deviation (θ14) from θ13 Oscillated Spectrum
<Excluded parameters>
Exclusion
region

22. Summary Summary We obtained an excluded parameter region for sterile
neutrino oscillation due to sin2(2θ14) and |Δm241|,
from 500 days of data sample.
The far-to-near ratio measurement of reactor anti-
neutrinos is used to reduce the flux and spectral
uncertainties.
We checked consistency with the standard three-
flavor neutrino oscillation model.

23. Back up Evaluation of reactor neutrino flux: issues and uncertainties
arXiv:
235U=53.8%, 239Pu=32.8%, Pu241=5.6% and U238=7.8%,
in fractions of fissions per isotope.
Back up

24. Expected Reactor Antineutrino Fluxes
Reactor neutrino flux
- Pth : Reactor thermal power provided by the YG nuclear power plant
- fi : Fission fraction of each isotope determined by reactor core simulation of Westinghouse ANC
- fi(En) : Neutrino spectrum of each fission isotope
[* P. Huber, Phys. Rev. C84, (2011)
T. Mueller et al., Phys. Rev. C83, (2011)]
- Ei : Energy released per fission
[* V. Kopeikin et al., Phys. Atom. Nucl. 67, 1982 (2004)]
* P.Huber PRD70, (2004)

25. 박사 과정 한일 논문(주저자) - 4편 국내 구두 발표 국내 포스터 발표 한국물리학회 6회 한국물리학회 4회 해외 포스터 발표
" Study of Neutron Capture Events Produced by Cosmic Muons in the RENO”, New Physics,
(2012)
" Development of a Gadolinium-loaded LAB-based Aqueous Scintillator for Neutrino Detection”,
JKPS, (2013)
"Development of a Gadolinium-loaded Liquid Scintillator for the Hanaro Short Baseline Prototype
Detector", JKPS, (2014)
"Study of the Monte Carlo Simulation Environment by Using Radioactive Sources in the RENO",
New Physics, (2014)
국내 구두 발표
국내 포스터 발표
한국물리학회 6회
한국물리학회 4회
해외 포스터 발표 3회
International Atomic Energy Agency, France, Dec. 2014
XXVII International Conference on Neutrino Physics and Astrophysics,
(Neutrino 2016)
38th International Conference on High Energy Physics, (ICHEP 2016)

26. <포스터> <구두 발표> 2012년 봄 학술논문발표회
->Study of neutron capture events produced by cosmic muons
2012년 가울 학술논문발표회
->Study of the RENO detector stability with cosmic muon induced events
2013년 봄 학술논문발표회
->Study of detection efficiency at RENO
2013년 가울 학술논문발표회
->Production of liquid scintillator for SBL prototype detector
2014년 봄 학술논문발표회
->Observed vs expected rates of reactor neutrinos at RENO
2014년 가울 학술논문발표회
->Search for sterile neutrinos at RENO
주최기관 : International Atomic Energy Agency
->Search for sterile neutrinos at RENO (poster at France, )
XXVII International Conference on Neutrino Physics and Astrophysics, (Neutrino 2016)
->Search for sterile neutrinos at RENO (poster at London, UK, )
38th International Conference on High Energy Physics, (ICHEP 2016)
->Search for sterile neutrinos at RENO (poster at Chicago, USA, )
<구두 발표>
2015년 봄 (가을) 학술논문발표회
Search for sterile neutrinos at RENO
2016년 봄 (가을) 학술논문발표회

27. Introduction -> Create additional oscillation modes
Great progress in the understanding of Pontecorvo-Maki-Nakagawa-
Sakata matrix has been made.
Three-neutrino mixing framework is well established, many experiments
results cannot be explained within the standard three-flavor framework.
It seems to require an additional neutrino with a mass.
(“LSND anomaly”, “Gallium anomaly”, ‘reactor antineutrino anomaly’,
“dark radiation and hot dark matter component”)
Daya Bay, Double Chooz, RENO show a similar deficit in the measured
electron antineutrino event rates.
Light sterile states can be mixed with active states through the mass
eigenstates.
-> Create additional oscillation modes

28. Sterile neutrino search at RENO
<θ13 &θ12 oscillation terms>
<θ14 oscillation terms>
Near : L~300m
Near : L~1400m
~1400m
<Ev>~4MeV
~300m
Sensitive at
Δm241 ~ 0.5×10-3eV2
Sensitive at
Δm241 ~ 0.2×10-2eV2

29. Expected Antineutrino Events from Reactor
Inverse Beta-Decay
Number of expected anti-neutrinos from reactor
Average cross section
IBD cross section
Prefactor κ
->From Beta-Decay of the free neutrons
(926 s -> s)
G. Mention et al. The Reactor Anti-neutrino
Anomaly, Phys. Rev. D 83, (2011).

30. Expected Antineutrino Events from Reactor
1. Antineutrino flux increase
235U (+2.5%), 239Pu(+3.1%), 238U(+9.8%), 241Pu(+3.7%)
2. Neutron lifetime decrease
(926 s -> s)
(10-43 cm2/fission)
Isotope
Old
New
235U
6.39±1.9%
6.61±2.11%
239Pu
4.19±2.4%
4.34±2.45%
238U
9.21±10%
10.10±8.15%
241Pu
5.73±2.1%
5.97±2.15%
+3.4%
+3.6%
+9.6%
+4.2%
G. Mention et al. The Reactor Anti-neutrino
Anomaly, Phys. Rev. D 83, (2011).
Increase of the expected reactor antineutrino rate in 2011

31. Expected IBD Templates Sources of systematic uncertainties
Inputs
Sources of systematic uncertainties
Uncertainties
(%)
Isotope fraction
0.7
Thermal power
0.5
Detection efficiency
0.2
Backgrounds (near)
(far)
0.14
0.35
Energy Scale
0.15
IBD MC Template
Oscillation parameters
Signal MC with 4 isotopes
Interaction fraction
Expected # of IBD
Detection efficiency
Dead time
Expected Far to Near ratio template
|Dm241| = 0.1 eV2
Expected Far to Near ratio template
sin22q14 = 0.1

32. Delayed Spectrum and Capture Time|
Delayed signal peak:
~2.2 MeV
Mean coincidence time:
~ 200 ms 32

33. Far/Near Shape Analysis for |Dmee2|
Observed
Far/Near
Expected
χ2 fitter
Fit using far-to-near ratio
(Work in progress)
1850 days of data
Minimize Χ2 Function
Energy-dependent disappearance of reactor antineutrionos

34. Results from Spectral Fit
(Work in progress)
Rate+shape
results
(± 8 %)
(± 6 %)

35. RENO Results
PRL 116, (2016)
Submitted to PRD (arXiv: )
500 days
systematic errors are greatly reduced due to larger statistics and efforts on background reduction
(Work in progress)
New results (~1850 days)

37. F. P. An et al., Phys .Rev.
Lett. 113, (2014)

38. Observation of an excess at 5 MeV
~2.5%
~2.5%

39. G. Mention et al. “The Reactor Anti-neutrino Anomaly”, Phys. Rev
G. Mention et al. “The Reactor Anti-neutrino Anomaly”, Phys. Rev. D 83, (2011).
Y. Declais et al., Nucl. Phys. B434, 503 (1995).

40. Make Template Inputs PhysRevLett. 116.211801
Oscillation Parameters : 14448개 Point
Signal MC w/ 4 isotopes Vr
/data_terminalB/hkseo/mc/ntuple
Interaction Fraction
/scratch/public/expected_flux/
isotope_fraction/150814
Dead Time : Vr
IBD MC template
Oscillation parameters
Signal MC w/ 4 isotopes
Interaction fraction
Expected # of IBD
Detection efficiency
Dead time
From RENO data
PhysRevLett.

41. Make Template Inputs sin2(2θ13)= 0.01~0.15 (dtheta 0.01)
The value of sin2(2 θ 14), sin2(2θ13), and |Δm241| were unconstrained.
Inputs
Oscillation Parameters : 14448개 Point
Signal MC w/ 4 isotopes Vr
/data_terminalB/hkseo/mc/ntuple
Interaction Fraction
/scratch/public/expected_flux/
isotope_fraction/150814
Dead Time : Vr
IBD MC template
Oscillation parameters
Signal MC w/ 4 isotopes
Interaction fraction
Expected # of IBD
Detection efficiency
Dead time
sin2(2θ13)= 0.01~0.15 (dtheta 0.01)
Before period : 개
After period : 개

42. Back up

43. Energy scale
<Example>

44. It can’t apply different parameter values in batches.
Energy scale
I was a fitting function dividing the period or using complex functions.
It can’t apply different parameter values in batches.
So, it chosen 0.15% of energy scale difference by interpolator method in the code.
Near1
Near2
Near3
Near4

45. Energy Scale
Far2
Far1
Near6
Near5
Far3
Far4
Far5
Far6

46. Exclusion contour Exclusion region No.1 No.2 ① ② ③ ④ ⑥ ⑤ ①, ②, ③, ④
Reno - 95% C.L.
Dayabay - exclusion
⑤, ⑥
Reno - exclusion
Dayabay - 95% C.L.
No.1
No.2

47. No.1 - ①
No.1 - ②

48. Comparison of RENO and DayaBay
<Theoretical calculation>
RENO
DayaBay
It showed different
trends by baseline
difference.
RENO
DayaBay

49. 1. Reactors by position
reactor1
reactor2
reactor3
reactor4

50. 1. Reactors by position
reactor5
reactor6
Total

51. No.1 - ③
No.1 - ④

52. Comparison of RENO and DayaBay
<Theoretical calculation>
RENO
DayaBay
It showed different
trends by baseline
difference.
RENO
DayaBay

53. 1. Reactors by position
reactor1
reactor2
reactor3
reactor4

54. 1. Reactors by position
reactor5
reactor6
Total

55. No.2 - ⑤
No.2 - ⑥

56. 1. Reactors by position reactor1 reactor2 reactor3 reactor4 reactor5

57. 2. Theoretical calculation
RENO
DayaBay

58. F. P. An et al., Phys .Rev.
Lett. 113, (2014)

59. Far prediction from near
RENO data
Dayabay data

60. RENO DayaBay Data It showed different trends by reno and dayabay data.

61. RENO data

62. RENO data

63. Survival Probability
RENO data
Mention (SBL)

64. Fixed sin2(2θ13) Exclusion contour 95% C.L. Exclusion region
RENO data (input data)

65. <sin2(2θ13)=0.01>
<sin2(2θ13)=0.02>

66. <sin2(2θ13)=0.03>
<sin2(2θ13)=0.04>

67. <sin2(2θ13)=0.05>
<sin2(2θ13)=0.06>

68. <sin2(2θ13)=0.08>
<sin2(2θ13)=0.09>

69. <sin2(2θ13)=0.10>
<sin2(2θ13)=0.11>

70. <sin2(2θ13)=0.12>
<sin2(2θ13)=0.13>
<sin2(2θ13)=0.14>

71. F. P. An et al., Phys .Rev.
Lett. 113, (2014)

72. Far prediction from near
Best-fit value

73. far
# of events %
near
reactor1
15.06
7.21
reactor2
17.13
16.42
reactor3
16.76
32.21
reactor4
19.03
28.67
reactor5
16.12
10.25
reactor6
4619.2
15.91
5.24
total
100.00
far
# of events %
near
reactor1
14.97
7.40
reactor2
17.12
16.40
reactor3
16.79
31.98
reactor4
19.08
28.47
reactor5
16.14
10.32
reactor6
15.88
5.44
Total
100.00
total

74. Fitting Chi^2 function for shape analysis - rate + shape analysis
Fixed theta13
Shape+Rate 0.20 MeV / bin
Sin2(2θ14)
(Χ 2 / d.o.f )
Stat. Error
Sys. Error
Total error
Before cf
(26.1/32=0.81 )
After cf
(30/32=0.93 )
Total
(56.9/66=0.86 )
Shape+Rate 0.20 MeV / bin
Δm241
Stat. Error
Sys. Error
Total error
Before cf
After cf
+ -nan
Total

75. Fitting Chi^2 function for shape analysis - rate + shape analysis
Shape+rate 0.20 MeV
/ bin
Sin2(2θ14)/(Χ 2 / d.o.f )
Stat. error
Sys. error
Total error
Total
(56/65=0.86)
Shape+rate 0.20 MeV
/ bin
Δm241
Stat. error
Sys. error
Total error
Total
The value of sin2(2 θ 14), sin2(2θ13), and |Δm241| were unconstrained.
(Chi-square fitting with 3 parameters)

76. Sterile neutrino mixing
Three-neutrino mixing UPMNS=R23(q23)R13(q13,d1)R12(q12)
Four-neutrino mixing UF = R34(q34)R24(q24,d2)R14(q14)R23(q23)R13(q13,d1)R12(q12,d3)
The survival probability of electron antineutrinos is given by
<θ13 &θ12 oscillation terms>
<θ14 oscillation terms>

77. <Oral presentation>
<Poster>
2012년 봄 학술논문발표회
->Study of neutron capture events produced by cosmic muons
2012년 가울 학술논문발표회
->Study of the RENO detector stability with cosmic muon induced events
2013년 봄 학술논문발표회
->Study of detection efficiency at RENO
2013년 가울 학술논문발표회
->Production of liquid scintillator for SBL prototype detector
2014년 봄 학술논문발표회
->Observed vs expected rates of reactor neutrinos at RENO
2014년 가울 학술논문발표회
->Search for sterile neutrinos at RENO
주최기관 : International Atomic Energy Agency
->Search for sterile neutrinos at RENO (poster at France, )
XXVII International Conference on Neutrino Physics and Astrophysics, (Neutrino 2016)
->Search for sterile neutrinos at RENO (poster at London, UK, )
38th International Conference on High Energy Physics, (ICHEP 2016)
->Search for sterile neutrinos at RENO (poster at Chicago, USA, )
<Oral presentation>
2015년 봄 (가을) 학술논문발표회
Search for sterile neutrinos at RENO
2016년 봄 (가을) 학술논문발표회