Results from
Reactor Neutrino Experiments
Soo-Bong Kim (KNRC, Seoul National University)“Tsukuba Global Science Week (TGSW2017), Tsukuba, Sep. 25-27, 2017”

Neutirno Oscillation

Neutrino oscillation
Bruno Pontecorvo(1913 - 1993)
1946: Proposal of neutrino detection using 37Cl
1957: Proposal of neutrino transformation(neutrino ↔ antineutrino)
1967/69: Proposal of neutrino flavor oscillation

1998

Neutrino Mixing Angles
Atmospheric
Neutrino Oscillation

Solar Neutrino
Oscillation

Reactor NeutrinoOscillation

θ23~45o (1998)

θ1234o (2001)

θ13Super-K; K2K

2015
Nobel
Prize

SNO, Super-K;
KamLAND

9o (2012)

Daya Bay, RENO
Double Chooz+ T2K (2011)2017

Pontecorvo
Prize“Neutrino has mass”“Established three-flavor mixing framework”

Impact of θ13 Measurement
 Definitive measurement of the last, smallest neutrino
mixing angle θ13 based on the disappearance ofreactor electron antineutrinos→ Open a new window for determining(1) CP violating phase, and(2) neutrino mass ordering
without a neutrino factory
For example, Hyper-Kamiokande(+ KNO), DUNE,JUNO, PINGU, INO, …..θ13 Impacts for Future Experiments
Accelerator
ReactorMOθ13 ≈ 9oRENO-50
MO = Mass Ordering

MOMO & δCP

MO & δCPPINGU

AtmosphereORCA

Neutrino Physics with Reactor
1956 Discovery of (anti)neutrino

Savannah River

2003 Observation of reactor neutrino oscillation (θ12 & ∆m212)

KamLAND

2012 Measurement of the smallest mixing angle θ13

Reactor Neutrinos
Reactor Neutrinos

Nuclear Power Plants~5×1020 ν/sec Cost-free, intense, low-energy &well-known neutrino source !

HanbitReactor θ13 Experiments
RENO at Yonggwang, Korea

Daya Bay at Daya Bay, China

Double Chooz at Chooz, Franceθ13 Reactor Neutrino Detectors

MOLS
Gd-LS

H2O

DBDCRENO

Comparisons of Reactor θ13 Experiments
Baselines

Reactor Thermal
Power (GWth)Daya BayRENO
Double Chooz

Target (ton)
80.00
60.00
40.00
20.00
0.00

010

20

Manpower
Daya BayRENO
Double Chooz
0.00 100.00 200.00 300.00
10

First θ13 measurements in 2012
~ 5 years ago
Double Chooz

Daya Bay

RENO

Publication

PRL 108, 131801(Mar. 30, 2012)

PRL 108, 171803(Apr.27, 2012)

PRL 108, 191802(May 11, 2012)

sin2(2θ13)

0.086

0.092

0.113

Stat. error

0.041

0.016

0.013

(101 days)(49 days)(220 days)

0.030

0.005

0.019

(flux uncert.)(MC driven)(data driven)

1.7 σ

5.2 σ

4.9 σ

Syst. error
Significance

1 month

2 weeks

RENO Collaboration
Reactor Experiment for Neutrino Oscillation(7 institutions and 40 physicists)
 Chonnam National University
 Dongshin University
 GIST Kyungpook National University
 Seoul National University
 Seoyeong University
 Sungkyunkwan University

 Total cost : $10M
 Start of project : 2006
 The first experiment runningwith both near & far detectors
from Aug. 2011

YongGwang (靈光) :RENO Experimental Set-up
120 m.w.e.
Near Detector

Far Detector
450 m.w.e.

The RENO Detector
Target : 16.5 ton Gd-LS(R=1.4m, H=3.2m)
 Gamma Catcher :MO

30 ton LSLS

(R=2.0m, H=4.4m)

H2OGd-LS 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

Detection of Reactor Antineutrinos

Gd capture or H capture~200 µs~ 2.2 MeV

 Prompt signal (e+) : 1 MeV 2γ’s + e+ kinetic energy (E = 1~10 MeV)
 Delayed signal (n) : 8 MeV γ’s from neutron’s capture by Gd or H
~30 μs or ~200 µs

Coincidence of prompt and delayed signals(prompt signal)(delayed signal)

Delayed signal

Prompt signal

n-Gd IBD~30 µs

8 MeV~200 µsn-H IBD
2.2 MeV16

Backgrounds
 Accidental coincidence between prompt and delayed signals
 Fast neutrons produced by muons, from surrounding rocks and insidedetector (n scattering : prompt, n capture : delayed)
 9Li/8He β-n followers produced by cosmic muon spallation
AccidentalsµγnGd

9Li/8He β-n followers

Fast neutronsµpGdnµ9Lien Gd17

New Results from RENO Observation of energy dependent disappearance of reactor
neutrinos to measure ∆mee2 and θ13 using ~1500 days of data
(Aug. 2011 ~ Sep. 2015)
 Measurement of absolute reactor neutrino flux using 1500days
 Observation of an excess at ~5 MeV in reactor neutrino
spectrum using ~1500 days of data

RENO Data-taking Status
 Data taking began on Aug. 1, 2011 withboth near and far detectors.
(DAQ efficiency : ~95%)
 A (220 days) : First θ13 result[11 Aug, 2011~26 Mar, 2012]
PRL 108, 191802 (2012)

ABNow

 B (403 days) : Improved θ13 result[11 Aug, 2011~13 Oct, 2012]
NuTel 2013, TAUP 2013, WIN 2013
 C (500 days) : First |∆mee2| result
Rate+shape analysis (θ13 and |∆mee2|)[11 Aug, 2011 ~ 21 Jan,2013]
PRL 116, 211801 (2016)
submitted to PRD (arXiv:1610.04326)
 D (1500 days) : New results[11 Aug, 2011 ~ Sep, 2015]

CD (1500 days)
Total 2000 days
19

Delayed Signals from Neutron Capture by Gd

Identical Performance of Near and Far Detectors
Spectra of Delayed Signals Using 252Cf SourceReduction of background rates & uncertainties
2Allows precise measurements of 𝑠𝑠𝑠𝑠𝑠𝑠2 2𝜃𝜃13 and Δ𝑚𝑚𝑒𝑒𝑒𝑒* Far : 2012 Oct. ~ 2015 Sep.

𝟗𝟗𝑳𝑳𝑳𝑳/ 𝟖𝟖𝑯𝑯𝑯𝑯
Accidental Fast
Neutron𝟐𝟐𝟐𝟐𝟐𝟐𝑪𝑪𝑪𝑪

𝟗𝟗𝑳𝑳𝑳𝑳/ 𝟖𝟖𝑯𝑯𝑯𝑯
Accidental Fast
Neutron𝟐𝟐𝟐𝟐𝟐𝟐𝑪𝑪𝑪𝑪• Accidentals : Additional cuts and improved flashing-PMT removal algorithms• Cosmogenic 9𝐿𝐿𝐿𝐿/ 8𝐻𝐻𝐻𝐻 : Optimized muon veto criteria• 252𝐶𝐶𝐶𝐶 contamination : Improved multiple-neutron removal algorithms

22

Measured Spectra of IBD Prompt Signal
RENO’s observation of5 MeV excess~2.5 %

Clear excess at 5 MeV~2.5 %
23

Correlation of 5 MeV Excess with Reactor Powertwo or threereactors are off

All the six
reactors are on

5 MeV excess
has a clear
correlation
with reactor
thermal power !

The 5 MeV excess
comes from reactors!
24

Correlation of 5 MeV excess with 235U isotope fraction
235U fraction corresponds to freshness of reactor fuelPreliminaryΔχ2 = 1.174
P-value = 0.240(Endof reactor cycle)

RENO 1500 days

Fit function
y=ay = a*x + b

χ21.407
0.233(Beginningof reactor cycle)

25

Measurement of Absolute Reactor Neutrino Flux
R (data/prediction) = 0.946 ± 0.021 (1500 days)• The flux prediction is with Huber + Mueller model• Flux weighted baseline at near : 411 m*Prediction is corrected for threeflavor 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Far/Near Shape Analysis
Energy-dependent disappearance of reactor antineutrinos

sin 2 2θ13 = 0.086 ± 0.006(stat.) ± 0.005(syst.)(± 9 %)

215−32 (± 7 %) 27∆m ee= 2.61−+00..16(stat.) −+00..09(syst.)(×10eV)09

Allowed regions in |∆mee2| and sin22θ1328

Observed L/E Dependent Oscillation

29

Summary of θ13 Results

More precise measurement of θ13 and |∆mee2|
PRL 116, 211801 (2016), Submitted to PRD (arXiv:1610.04326)

500 days

MeanStat.

Sys.

Precision

𝐬𝐬𝐬𝐬𝐬𝐬𝟐𝟐 𝟐𝟐𝛉𝛉𝟏𝟏𝟏𝟏

0.082+0.009-0.009+0.006-0.00612 %

2.62+0.21-0.23+0.12-0.13

10 %|∆mee2|(x10-3 eV2)

New results (preliminary)1500 days

Mean

Stat.

Sys.

Precision

𝐬𝐬𝐬𝐬𝐬𝐬𝟐𝟐 𝟐𝟐𝛉𝛉𝟏𝟏𝟏𝟏

0.086+0.006-0.006+0.005-0.0059%2.61+0.15-0.16

+0.09
-0.09

7%

|∆mee2|(x10-3 eV2)

Systematic errors are reduced due to background
reduction and larger statistics of control samples

31

RENO : Plan and Prospects
Plan for RENO data taking
2017

2018

RENO data will be taken for 2
more years from now and it willtake 3 additional years for theanalysis.

2019

2020

2021

Possible extension of additional 2~3 years

sin22θ13 and |∆mee2| will approach to~6% precision (our design goal).

According to our recent study, thesystematic error of |∆mee2| is smaller
than the statistical error.

500 days
Measured1500 days
Measured(preliminary)~3000 days
Expectedsin22θ13

12 %

9%

~5%

|∆mee2|

10 %

7%

4~5%

32

θ13 & |∆m2ee| in Daya Bay
Neutrino 2016

1230 days data33

θ13: Double Chooz
JHEP 10 (2014) 086

468 daysAssuming ∆m231 = MINOS result
34

Future Prospects on θ13Double Chooz
Data
3 yrs Near&Far
Δ(sin2(2θ13))~10 %Δ(|m2ee|)
-RENO
5 yrs
~5 %
~5 %

Daya Bay
6 yrs
~3 %
~3 %

J. Cao @TAUP2015

FroST 2016 @Fermilab

35

Summary More precise measurements of θ13 and ∆mee2 using energy
dependent disappearance of reactor neutrinos

sin 2 2θ13 = 0.086 ± 0.006(stat) ± 0.005(syst) ± 0.008−3152∆m ee2 = 2.61−+00..16×(stat.) −+00..09(syst.)(10eV)
09± 0.18

9 % precision

7 % precision Measured absolute reactor neutrino flux : R= 0.946±0.021
 Observed an excess at 5 MeV in reactor neutrino spectrum
 sin2(2θ13) and ∆mee2 to 6% accuracy after 2 more years data taking
 Additional 2~3 years of data taking under consideration to improve∆mee2 accuracy

Thanks for your attention!

Reactor Neutrino Oscillations
νeνeνeνe

Probability νeνe

νe1.0Oscillations observed as adeficit of anti-neutrinos
the position of theminimum is defined byΔm2ee
sin22θ13

flux before oscillation
observed here

Distancecos 2 𝜃𝜃12 Δ𝑚𝑚221

1200 to 1800 meters

Energy Calibration from γ-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))