Current Results from Reactor Neutrino
Experiments
Soo-Bong Kim (KNRC, Seoul National University)“Tsukuba Global Science Week (TGSW2015), Tsukuba, Sep. 28-30, 2015”

Neutrino Physics with Reactor
1956 Discovery of (anti)neutrino

Savannah River

2003 Observation of reactor neutrino oscillation (12 & m212)

KamLAND

2012 Measurement of the smallest mixing angle 13
IBD rate ( /day)

1000

Expected with no oscillation
Expected with oscillation (best fit)

500

Near Detector
10050

Far Detector02011 Aug

2012 Jan2012 July

2013 Jan2013 July

2014 JanReactor Neutrinos
Reactor Neutrinos

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

HanbitReactor 13 Experiments
RENO at Yonggwang, Korea

Daya Bay at Daya Bay, China

Double Chooz at Chooz, France13 Reactor Neutrino Detectors

MOLS
Gd-LS

H2O

RENO Collaboration
Reactor Experiment for Neutrino Oscillation(11 institutions and 40 physicists)
 Total cost : $10M
 Chonbuk National University
 Start of project : 2006
 Chonnam National University
 The first experiment running Chung-Ang University
with both near & far detectors
 Dongshin University
from Aug. 2011
 GIST Gyeongsang National University
 Kyungpook National University
 Sejong University
 Seoul National University YongGwang (靈光) : Seoyeong University
 Sungkyunkwan University

RENO Experimental Set-up
120 m.w.e.
Near Detector

Far Detector
450 m.w.e.

RENO Status
 Data taking began on Aug. 1, 2011 withboth near and far detectors.
(DAQ efficiency : ~95%)
 A (220 days) : First 13 result[11 Aug, 2011~26 Mar, 2012]
PRL 108, 191802 (2012)

Near Detector
1400 days of dataA B (403 days) : Improved 13 result[11 Aug, 2011~13 Oct, 2012]
NuTel 2013, TAUP 2013, WIN 2013

 C (~800 days) : New result

Shape+rate analysis (13 and mee2)[11 Aug, 2011~31 Dec, 2013]

 Total observed reactor neutrino events asof today : ~ 1.5M (Near), ~ 0.15M (Far)→ Absolute reactor neutrino flux
measurement in progress[reactor anomaly & sterile neutrinos]

Far Detector
BC(new results)

Now

Detection of Reactor Antineutrinos(prompt signal)γ(0.511MeV)e-(delayed signal)~180 s+ p  D +  (2.2 MeV)
~28 s
(0.1% Gd) + Gd  Gd + ‘s (8 MeV) Neutrino energy measurementγ(0.511MeV)e+νeprompt signal

pn
Delayed signal

30μsγγ E ~ 8MeVGdγγNew RENO Results■ ~800 days of data
■ New measured-value of 13from rate-only analysis■ Observation of energy dependent disappearance of reactor

neutrinos to measure mee2 and 13 (work in progress)■ Observation of an excess at 5 MeV in reactor neutrino

spectrumImprovements after Neutrino 2014
 Relax Qmax/Qtot cut : 0.03 → 0.07
- allow more accidentals to increase acceptance of signal and minimize
any bias to the spectral shape More precisely observed spectra of Li/He background- reduced the Li/He background uncertainty based on an increased
control sample
 More accurate energy calibration- best efforts on understanding of non-linear energy response and energy
scale uncertainty
 Elaborate study of systematic uncertainties on a spectral fitter- estimated systematic errors based on a detailed study of spectral fitterin the measurement of mee2

Neutron Capture by Gd

Measured Spectra of IBD Prompt Signal

Bkg.: 5.6 %Near Live time = 761.11 days
# of IBD candidate = 470,787# of background = 26,375 (5.6 %)Bkg.: 12.0 %Far Live time = 794.72 days
# of IBD candidate = 52,250# of background = 6,292 (12.0 %)Observed Daily Averaged IBD Rate
IBD rate ( /day)

1000

Expected with no oscillation
Expected with oscillation (best fit)

500

preliminary

Near Detector
10050

Far Detector
02011 Aug2012 Jan2012 July

2013 Jan2013 July

2014 Jan Good agreement with observed rate and prediction.
 Accurate measurement of thermal power by reactor neutrinos

Observed vs. Expected IBD Rates- Good agreement between observed rate & prediction- Indication of correct background subtraction

New 13 Measurement by Rate-only Analysis(Preliminary)sin 2 2θ13  0.087  0.008(stat.)  0.008(syst.)
Uncertainties
sources

Uncertainties (%)

Errors of sin2213(fraction)

Statistics (near)(far)

0.21 %
0.54 %

0.0080

Systematics (near)
(far)

0.94%
1.06%

0.0081

Reactor

0.9 %Detection efficiency

0.2 %Backgrounds (near)(far)

0.14 %
0.51 %

0.0032 (39.5 %)0.0037 (45.7 %)0.0070 (86.4 %)Observation of an excess at 5 MeV

~2.5%

~2.5%

Correlation of 5 MeV Excess with Reactor Power
5 MeV excess
has a clear
correlation
with reactor
thermal power !
two or threereactors are off

All the six
reactors are on

A new reactor neutrino
component !!

** Recent ab initio calculation [D. Dwyer and T.J. Langford, PRL 114, 012502 (2015)] :‐ The excess may be explained by addition of eight isotopes, such as 96Y
and 92RbThe 5 MeV Excess Seen at Double-Chooz
and Daya Bay

Daya Bay, ICHEP 2014

Double‐Chooz, Neutrino 2014

Why n-H IBD Analysis?
Motivation:
1. Independent measurement of 13 value.
2. Consistency and systematic check on reactor neutrinos.

* RENO’s low accidental background makes it possible
to perform n-H analysis.
-- low radio-activity PMT-- successful purification of LS and detector materials.

IBD Sample with n-H
preliminaryn-H IBD Event Vertex Distribution
target-catcher

NearFarLive time(day)379.663384.473

IBD Candidate

249,799

54,277

IBD( /day)

619.91667.823

Accidental ( /day)

25.16±0.4268.90±0.35

Fast Neutron( /day)

5.62±0.30

1.30±0.08

LiHe( /day)

9.87±1.48

3.19±0.37

Results from n-H IBD sample
Very preliminary
Rate-only result(B data set, ~400 days)sin 2θ13  0.103  0.014(stat.)  0.014(syst.)
2(Neutrino 2014) sin 2 2θ13  0.095  0.015(stat.)  0.025(syst.)← Removed a soft neutron backgroundand reduced the uncertainty of the accidental background
preliminary

preliminary

Near Detector

Far DetectorReactor Neutrino Oscillations
νeνe

νe

νe

Probability νeνeOscillations observed as adeficit of anti-neutrinos
the position of theminimum is defined byΔm2ee

νe1.0

sin22θ13

flux before oscillation
observed here

DistancecosΔ

21200 to 1800 meters

Energy Calibration from -ray SourcesB12 Energy Spectrum (Near & Far)

Energy Scale Difference between Near & Far

Energy scale difference < 0.15%

Far/Near Shape Analysis for mee2(work in progress)

Results from Spectral Fit(work in progress)2

 m ee  [2.52  0.19(stat)  0.17(syst) ] x10 -3 eV 2

sin 2 2θ13  0.088  0.008(stat )  0.007(syst )Systematic Errors of 13 & mee2(work in progress)sin 2 2θ13  0.088  0.008(stat )  0.007(syst )2(± 11 %) m ee  [2.52  0.19(stat)  0.17(syst) ] x10 -3 eV 2(± 10 %)

Errors of sin2213

Errors of mee2

0.21 %
0.54 %

0.008

0.19

Total Systematics

0.94 %
1.06 %

0.007

0.17

Reactor

0.9 %0.0025 (34.2 %)‐Detection efficiency

0.2 %0.0025 (34.2 %)‐Energy scale diff.

0.15 %*

0.0015 (15.6 %)0.07

Backgrounds (near)(far)

0.14 %
0.51 %

0.0060 (82.2 %)0.15

Uncertainties
sources

Uncertainties (%)

Statistics (near)(far)(* tentative)(x 10-3 eV2)

Observed L/E Dependent Oscillation(work in progress)

Double Chooz Results 2011.4 – 2013.1 (460 days) : No near site detector until 2014.11
 Spectral analysis for n-Gd & n-H samples
 Reactor-off data for direct measurement of backgrounds

 R+S : sin2213 = 0.090+0.032-0.029

Daya Bay Results 2011.12 – 2013.11 (621 days) Rate+Spectral analysis for n-Gd sample
 Rate analysis for n-H sample

Projected Sensitivity of 13 & mee2
NDM 2015

sin2 213  0.088  0.011
 0.005(5 % precision)(~800 days)(5 years of data)* Expected precision of mee ~ 0.1×10-3 eV2(~ 4% precision)
2012. 42013. 32013. 92014. 62015. 6

(5 % precision)(sensitivity goal of 13 )33

Future Prospects on 13 & mee2
 Precision dominated by statistics
 Continued efforts on improving systematics
 Expected ultimate precision :Experiments
Daya BayRENO
Double Chooz

(sin2213)±0.003 (±3%)±0.005 (±5%)±0.010 (±10%)mee) [×10-3 eV2]±0.07 (±3%)±0.1 (±4%)

3413 from Reactor and Accelerator Experiments
First hint of δCP combining
Reactor and Accelerator data
Best overlap is forNormal hierarchy & δCP = - π/2
Is Nature very kind to us?
Are we very lucky?
Is CP violated maximally?

Strong motivation foranti-neutrino run and precisemeasurement of θ13(T2K: PRL 112, 061802, 2014) 35

Summary
 Observed an excess at 5 MeV in reactor neutrino spectrum
 New measurement of 13 by rate-only analysis

sin 2 2θ13  0.087  0.008(stat )  0.008(syst )(preliminary) Observation of energy dependent disappearance of reactor
neutrinos and our first measurement of mee2

sin 2 2θ13  0.088  0.008(stat )  0.007(syst )2-3

 m ee  [2.52  0.19(stat)  0.17(syst) ] x10 eV2(work in progress)

 Measurement of 13 from on n-H IBD analysis

sin 2 2θ13  0.103  0.014(stat )  0.014(syst )(preliminary) sin(213) to 5% accuracy
mee2 to 0.1×10-3 eV2 (4%) accuracy within 3 years

Overview of RENO-50
 RENO-50 : An underground detector consisting of 18 kton ultralow-radioactivity liquid scintillator & 15,000 20” PMTs, at 50 km awayfrom the Hanbit(Yonggwang) nuclear power plant Goals : - Determination of neutrino mass ordering- High-precision measurement of 12, m221 and m2ee- Study neutrinos from reactors, the Sun, the Earth, Supernova, andany possible stellar objects

 Budget : $ 100M for 6 year construction(Civil engineering: $ 15M, Detector: $ 85M)

 Schedule : 2015 ~ 2020 : Facility and detector construction
2021 ~: Operation and experimentDetermination of Neutrino Mass Hierarchy• Reactor experiments: JUNO and RENO-50- Subdominant oscillation pattern of m312- Large liquid scintillator detector with a baseline of ~50 km- Extraordinary energy resolution (<3% at 1 MeV)
• Long baseline beam experiments: T2K, NOvA, T2HK andLBNE- Matter effects of neutrino oscillation- Small value of |m322|/E & long baseline L• Atmospheric neutrino experiments with Mton scale : HK,LBNE, MEMPHIS, PINGU and INO- Matter effects of neutrino oscillation- Small value of |m322|/E & long baseline L

Reactor Neutrino Oscillations at 50 km
Neutrino mass hierarchy (sign of m231)+precise values of 12, m221 & m2ee

Precise m221
Large Deficitsin 2122Ripple

cos231 sin2 21  1 sin 231 sin 2212

Precise 12Mass Hierarchy

Near Detector

Far Detector(NEAR Detector)(FAR Detector)

RENO-50
10 kton LS Detector~47 km from YG reactors
Mt. Guemseong (450 m)~900 m.w.e. overburdenVarious Physics with RENO-50
 Precise (<1%) measurement of 12, m221 and m2ee- Provide an interesting test for unitarity- Essential for the future discoveries Neutrino burst from a Supernova in our Galaxy- ~5,600 events (@8 kpc) (* NC tag from 15 MeV deexcitation )- Study the core collapsing mechanism with neutrino cooling Geo-neutrinos : ~ 1,000 geo-neutrinos for 5 years- Study the heat generation mechanism inside the Earth Solar neutrinos : with ultra low radioacitivity- MSW effect on neutrino oscillation- Probe the center of the Sun to study the metallicity problem

 Detection of J-PARC beam : ~200 events/year

J-PARC neutrino beam
Dr. Okamura & Prof. Hagiwara

Thanks for your attention!

Experimental site44