Variation of Observed Reactor
Antineutrino Yield at RENO

Jan. 17th, 2019
Seminar at TCHoU
Soo-Bong Kim (SNU/Foreign
Research Unit PI at U of Tsukuba)

Nuclear Fission ProductsElectron Antineutrino are produced from !-decay of reactor fuels;
Mainly "#$%, "#&%, "#'() and "*+()~ 200 MeV/fission~ 6 ne/fission
1 GWth reactor
à ~2x1020 ne/sec

Reactor Fuel Isotope Fraction
Average fission fraction!"#$ : !"#%: !"#& : !"'( = 0.573 : 0.299 : 0.073 : 0.055

The Fission fraction of an isotope varies with fuel-burningReactor for Antineutrino Source
Reactor: A copious and isotropic source of electron antineutrinos~3 GWth or ~1 GWelec per reactor

3 GWth reactor
à ~6x1020 ne/sec• 3-4% accurate neutrino source• 0.13% uncertainty of IBD crosssection[* P. Huber, Phys. Rev. C84, 024617 (2011)
T. Mueller et al., Phys. Rev. C83, 054615 (2011)]

Observable Reactor Neutrino Spectrum

Neutrino Physics with Reactor
1956 Discovery of (anti)neutrino

Nobel Prizein 1995

Savannah River

2003 Observation of reactor neutrino oscillation (q12 & Dm212)

KamLAND

2012 Measurement of the smallest mixing angle q13
IBD rate ( /day)

1000

Expected with no oscillation
Expected with oscillation (best fit)

500

Near Detector
10050

Far Detector
02011 Aug2012 Jan2012 July

2013 Jan2013 July

2014 JanNeutrino Oscillation
Wolfgang Pauli(1900 - 1958)
Invention of neutrino

Frederick Reines(1918 - 1998)
Detection of neutrino

Bruno Pontecorvo(1913 - 1993)
Invention of neutrino oscillation

Neutrino oscillation

1998

Neutrino Mixing Angles
Atmospheric
Neutrino Oscillation

Solar NeutrinoOscillation

Reactor Neutrino
Oscillation

q23
q12

q13~45o (1998)
Super-K; K2K

2015
NobelPrize

34o (2001)
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 q13 Measurement§ Definitive measurement of the last, smallest neutrino
mixing angle q13 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, …..

Reactor q13 Experiments
RENO at Yonggwang, Korea

Daya Bay at Daya Bay, China

Double Chooz at Chooz, Franceq13 Reactor Neutrino Detectors

MOLS
Gd-LS

H2O

DB

DCRENO

Comparisons of Reactor q13 Experiments
Baselines

Reactor Thermal
Power (GWth)Daya BayRENO
Double Chooz

Target (ton)1020

Manpower
Daya BayRENO
Double Chooz

Double…
RENO
DayaBay80.00
60.00
40.00
20.00
0.00

00.00 100.00 200.00 300.00
12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
0m
29m
80
13

Far Detector
450 m.w.e.

The RENO Detector§Target : 16.5 ton Gd-LS(R=1.4m, H=3.2m)§ Gamma Catcher :MO30 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

RENO Data-taking Status§ Data taking began on Aug. 1, 2011 withboth near and far detectors.
(DAQ efficiency : ~95%)§ A (220 days) : First q13 result[11 Aug, 2011~26 Mar, 2012]
PRL 108, 191802 (2012)

AB§ B (~500 days) : Recent results
Rate+shape analysis (q13 and |Dmee2 |)5 MeV excess[11 Aug, 2011~21 Jan, 2013]→ PRL 116, 211801 (2016)
PRD 98, 012002 (2018)§ C (~2200 days) : New results
Rate+shape analysis (q13 and |Dmee2 |)Variation of reactor neutrino yield
5 MeV excess from 235U
[11 Aug, 2011~7 Feb, 2018]→ (arXiv:1806.00248 & arXiv:1806.00574)

Now

C (new results)
16

New Results from RENO
§ Precise measurement of |Dmee2 | and q13 using ~2200 daysof data (Aug. 2011 – Feb 2018)“Measurement of Reactor Antineutrino Oscillation Amplitude and Frequency
at RENO” (Phys. Rev. Lett. 121, 201801 (2018. 11. 15))

§ Fuel-composition dependent reactor antineutrino yield andspectrum“Fuel-composition dependent reactor antineutrino yield and spectrum atRENO” (arXiv:1896.00574)§ Independent measurement of q13 with delayed n-H IBD analysis

Detection of Reactor Antineutrinos

Gd capture or H capture~200 µs~ 2.2 MeV

§ Prompt signal (e+) : 1 MeV 2g’s + e+ kinetic energy (E = 1~10 MeV)
§ Delayed signal (n) : 8 MeV g’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 MeV19

Delayed Signals from Neutron Capture by Gd

Identical Performance of Near and Far Detectors
Spectra of Delayed Signals Using 252Cf Source

Measured Spectra of IBD Prompt Signal
Clear excess at 5 MeV

2.6±0.1 %Near Live time = 1807.88 days
# of IBD candidate = 850,666
Background : 2.03±0.06%

2.4±0.2 %Far Live time = 2193.04 days
# of IBD candidate = 103,212
Background : 4.76±0.20%

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!
23

Reactor Neutrino Oscillations

Δ"#$# term is negligible compared to Δ"%% # term for ~1km baseline.
(Δ"#$ # ∼ 7.5 ×10-. /0 # , Δ"%% # ∼ 2.5 ×10-2 /0 # )sin# (2θ$2 ) is determinedby oscillation amplitude.
Δ"%% # is determined bymaximum oscillationenergy (frequency).

Measurement of |Dmee2| and q13
Energy-dependent disappearance of reactor antineutrinos

Measurement of |Dmee2| and q13<500 days><2200 days>

sin$2&'( = 0.0896 ± 0.0048 stat. ± 0.0048(syst. ) (± 7.6 %)Δm$88 = 2.68 ± 0.12 stat. ± 0.07 syst. (×10<(eV$) (±265.2 %)Observed L/E Dependent Oscillation% 2 L (P(ν e → ν e ) ≈ 1− sin 2θ13 sin ' Δmee
*4Eν )&2227

Comparison of q13 and |Dmee2| Results

Evolution of Fuel Composition
Effective fission
fraction of 235U
(weighted by eachreactor’s thermal
power and fissionfraction)
8 groups of near IBD
samples with equal
statistics according to
235U isotope fraction

Effective Fission fraction
for each isotope

Predicted IBD Yield per Fission
IBD yield per fission for each isotpoe(Total # of produced IBD events)!" = $ % &' (" &' )&'IBD cross Antineutrino
section spectrum(i : each isotope)(H-M model)

Average IBD yield per fission(for each 8 group, j)

H-M model(10,-. cm2/fission)-!45,7 = 8 :4",7 !""93: Effective Fission fraction
for each isotope!/.0

6.70 +- 0.14!/.1

4.38 +- 0.11!/.2

10.07 +- 0.82!/-3

6.07 +- 0.13

30

Fuel-Composition Dependent Reactor Neutrino Yield# of Observed IBD
Measured IBD yield # ofper fission
Target proton

Detection
Efficiency# of fission

Total averaged IBD yield per fission (!
"# ) = (5.84 ± 0.13)×10-43 cm2/fission
0.940 ± 0.021 à (6.0 ± 2.1)% deficit
Averaged IBD yield perfission (!
"# ) vs %$&,(à slope means different
neutrino spectrum for eachisotope
à rules out the no fueldependent variation at 6.6)
The scaled model indicatesthe reactor antineutrino
anomalyMeasurement of !235 and !239
The best-fit measured yields per fission of 235U and 239Pu
The best-fit value of !"#$ :2.8 % deficit
6.15 ± 0.19/6.70 ± 0.14
The best-fit value of !"#& :0.8 % deficit
4.18 ± 0.26/4.38 ± 0.11
Reevaluation of the !"#$
may mostly solve the reactor
antineutrino anomaly.
But 239Pu is not entirely ruledout as a possible source of32theanomaly.

Correlation of 5 MeV excess with fuel 235U
2.9s indication of 5 MeV excess coming from 235U fuelisotope fission !!

(2.56±0.06) %(Endof reactor cycle)(Beginningof reactor cycle)

33

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

targetg-catcher34

Delayed Spectrum and Capture Time§ Delayed signal peak:~2.2 MeV§ Mean coincidence time:~ 200 µs35

q13 Measurement with n-H

sin22θ13 = 0.085±0.008(stat.)±0.012(syst.)
36

Reactor Neutrino Detector for Denuclearization
Rachel Carr et al., “Neutrino
physics for Korean diplomacy”,
Science 362, 649 (Nov. 2018)

Mobile Antineutrino Detector
MiniCHANDLER, Jonatnan Link

Summary§ Observation of energy dependent disappearance of reactor
neutrinos and improved measurement of and |Dmee2 | and q13

sin 2 2θ13 = 0.0896 ± 0.0048(sta t) ± 0.0048(sys t) ± 0.0068 7.6 % precisionΔm2ee = 2.68 ± 0.12(stat) ± 0.07(syst) (´10-3 eV2 )± 0.14

5.2 % precision§ Observation of fuel-composition dependent variation of IBD yield
at 6.6s CL§ First hint for 2.9s correlation between 5 MeV excess and 235U
fission fraction§ Measurement of q13 using n-H IBD analysis

Thanks for your attention!

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 b-n followers produced by cosmic muon spallation
Accidentalsµgn
Gd9Li/8He b-n followers

Fast neutronsµpGdnµ9Lien Gd41

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))