Detection of Coherent Elastic Reactor
Neutrino Scattering & Search for
Sterile Neutrino

Jan. 10, 2020
Soo-Bong KimSeoul National University/TCHoU, Univ. of Tsukuba

Overview
Development of a Bolometric Detector “LOCOND”
For Coherent Reactor Neutrino Elastic Scattering (CEvNS)-Use a low-radioactivity & phonon sensitive CsI(Na) or HPGe crystals for
sufficient CEvNS
Use a cryogenic sensor such as STJ or TES to have an energy threshold as
low as ~10 eV

Detection of reactor antineutrino below 1.8 MeV via CEvNSOpen a new field of detecting extremely low-energy neutrinos that have neverbeen observed• Searches for neutrino magnetic moment and sterile neutrino• Reactor monitoring for nuclear non-proliferation• Compact neutrino telescope for core-collapse supernova* LOCOND: LOw temperature COherent Neutrino Detector

Neutrino Sources and Reactor Neutrino

Unexploredregion !!

* Taken from Katz & Spiering (2012)Unobserved Low-Energy Reactor Neutrino
Reactor : copious source of electron antineutrinos

3 GWth reactor→ ~6x1020 ne/secReactor neutrino flux
IBD inelastic scattering

Reactor neutrinos with
E>1.8 MeV observed by
IBD inelastic reaction
Unobserved
reactor neutrino
Can be observed by“elastic” scatteringEnhancement of Low-Energy Neutrino Cross Section
Coherent Elastic Neutrino-Nucleon Scattering (CEvNS)
Extremely difficult to detect low energy (En) neutrinos→ lower cross section (~ En2)
→ need a large detector and a high flux of neutrinos!

n+N→n+N

Z-exchange of a neutrino with nucleus :→ Coherent up to En ~ 50 MeV(coherent length ~ 1/ En)→ Nucleus recoils as a whole~ N2~NN≈40 → N2=1600 → detector mass 10 t → a few kg
Enhanced (~100 times) neutrino cross section
at low energy (D.Z. Freedman, 1974)

Enhanced Neutrino Cross Section via CEvNS

A neutrino becomes coherent
up to ~50 MeV.

CsI and Ge crystals can provide
sufficient CEvNS cross sections.

Challenge: Tiny Nuclear Recoil Energy▪ Extremely low recoil energy (~ keV) for a heavy, neutron-rich nucleus
En = 10 MeV → Tmax ≈ 3 keV (in Ge)
50 MeV →75 keV
1 MeV →30 eV
Nuclear recoil energy spectrum in Ge for 30 MeV neutrino

Neutrino Sources for CEvNS Detection

Pros and cons for coherent neutrino scattering measurements of reactor andpion decay-at-rest
SourceFlux
ν’s per second

Reactor2x1020per GW𝜈𝑒1x1015

𝜈𝜇𝜈𝑒
𝜈𝜇

Stopped-pion(DAR)

FlavorEnergyPros< 8 MeV▪ huge flux

< 50 MeV▪ higher cross section▪ higher energy recoil▪ pulsed beam
▪ multiple flavorsCons▪ lower cross section▪ low energy recoil▪ steady-state▪ lower flux
▪ in-time neutrinos[taken from the presentation by Kate Scholberg at 2nd Workshop on Germanium
Detectors and Technologies, J. of Phys: Conference Series 606 (2015) 012010.]

Expected Reactor Antineutrino CEvNS• Quite low nuclear recoil energy in Ge: <2~3 keV• Even more enhanced CEvNS cross section• Intense neutrino flux near reactor core

▪ Reactor antineutrinos (in Ge)[En = 0 - 8 MeV]
En = 8 MeV → Tmax ≈ 2 keV
3 MeV →
270 eV
1 MeV →30 eV▪ DAR neutrinos (in Ge)[En = 0 - 50 MeV]
En = 50 MeV → Tmax ≈ 75 keV
30 MeV →27 keV

CEvNS reactor neutrino

DAR neutrino< ~300 eV <~30 keV

Observation of Coherent Elastic Neutrino Scattering
SCIENCE 357, no. 6356,1123-1126 (2017)-

14 kg CsI scintillating crystal
35 kg single phase LAr detector
185 kg NaI scintillating crystal
10 kg HPGe PPC detector

stopped p beam 30-50 MeV n source

Worldwide Efforts on Reactor Neutrino CEvNS
ExperimentTechnology

Threshold(eV)

Mass(kg)

Location

CONNIESi CCD~400.1Brazil

CONUS

HPGe3004GermanyMIνER

Ge/Si cryogenic~10010USANu-Cleus

Cryogenic CaWO4,
Al2O3 calorimeter array~200.01~0.1

Europe1 g underdevelopment

νGEN

Ge PPC350

1.6

RussiaUnder preparation

RED-100

LXe dual phase

1000~100

RussiaUnder preparation

RICOCHETGe, Zn bolometers100

1France

Under development

TEXONO

p-PC Ge~100.5~1.0

TaiwanUnder development

LOCOND

HPGe or CsI(Na) withTES cryogenic sensor~1020~30

Korea

Under proposal* LOCOND: LOw temperature COherent Neutrino Detector

Status
1 g underdevelopment
Data taken for nosignal observed
Under development

Significance of Reactor Neutrino CEvNS Detection
Establish a new field of detecting unexplored energy region of neutrinos▪ Explore a new region of neutrino magnetic moment▪ Efficient search for existence of sterile neutrino by neutral current▪ Practical and peaceful application such as reactor monitoring for
nuclear non-proliferation▪ Development of a compact neutrino telescope sensitive to detection of
an intense neutrino burst from a nearby core-collapse supernova▪ Precise measurement of nuclear form factors F(Q2)▪ Neutrino’s non-standard interaction (NSI) search▪ CEvNS solar neutrino detection as a neutrino floor of direct dark-mattersearches▪ Precise measurement of sin2θW at low energies

Motivation for Mobile Reactor Neutrino Detector
The reactor neutrino community and IAEA are eager to develop a compact andmobile antineutrino detector that can be used for peaceful and practical purposes.

Core Idea: Development of LOCOND Detector
Requirements for Low temperature Coherent Neutrino Detector :- Mobile CEvNS reactor antineutrino detector- Low energy threshold for nuclear recoil energy(should be < 2 keV (270 eV) to detect CEvNS with E < 8 (3) MeV &< 50 eV to observe neutrinos with E < 1.8 MeV)
- Sufficient neutrino target mass
- High-purity and low-radioactivity neutrino target- Efficient neutron shielding and veto component▪ Use 20~30 kg of scintillating CsI(Na) or ionizing radiation PPC
Ge crystals as a phonon (lattice vibration) excitation detector.
▪ Use a cryogenic sensor for phonon detection.
▪ Detect both phonons and photons (or e-h pairs) coming from therecoil energy in the crystal in order to obtain the energy thresholdat 10 eV.

High Performance Crystal as Neutrino Target▪ Use a scintillating CsI(Na) or ionizing PPC Ge crystal that
contains a heavy, neutron-rich nucleus providing sufficient
CEvNS cross section and reasonable recoil energy (<2 keV).

Detection of Phonon and Photon/Ionization▪ A simultaneous measurement of both heat and scintillation
enables significant reduction of backgrounds and particle
identification (𝛽/𝛾 and 𝛼) in order to achieve a nuclear recoil
energy threshold as low as 10 eV.
Phonon & Photon Cryogenic Detector

Phonon & Ionization Cryogenic Detector

SuperCDMSCaWO4CRESST-II

R&D for Ge Ionization Amplification
Development of Ge planar strip detector-Participation ininternational collaborative efforts

Charge amplification by electric fieldof 105 V/mObtain recoil energy threshold as low
as 10 eV with liquid nitrogen coolingCryogenic Bolometric Detector▪ A thermal signal from nuclear recoil energy is observed by acryogenic phonon sensor (STJ or TES) and used todetermine the energy deposited.

vacuumHeat bath
STJ photon sensor

scintillator

Target crystal
Reflective andscintillating housing

Experimental volume
 44 cm x 60 cm tall

Heat bath

TES phonon sensor

Section view of 104 Olympus ADR cryostat showing pulse-tube
head, adiabatic demagnetization refrigerator ( 55 cm x 110 cm)

Multi-pixel STJ Array Detector

Expected Nuclear Recoil Energy Threshold▪ Efforts on lowering the recoil energy threshold to a few tens of eV.

Final Goal
1st Goal(~2022)Done(~2014)

Ge-ionization
development▪ Light yield of CsI(Na) at cryogenic temperature ~8K : x5 enhancement from 54/keV

Efficient Neutron Shielding and Active Veto▪ Low-cost and efficient solution for a mobile detector- Radio-pure passive shielding: paraffin, Cu and Pb- light and efficient neutron-shielding materials: borated PE,Gd-loaded
boron carbide(B4C), or high-boron steel.
LSCryostat▪ Use active veto detector
components:
Cu(1) Gd or Li loaded scintillationveto detector with high neutron
capture probability, and (2) plastic scintillator plates in order to
identify and reject ambient gamma-rays and cosmic muonscoming into a detector.

* Borrowed from CONUS

Research Programs and Schedule
Development of CEvNS reactor Antineutrino Detector
CEvNS observation ofreactor neutrino at
nuclear power plant(2025)

CEvNS detection of HANARO
research reactor neutrino withLOCOND(2023-2024)(2021)

CEvNS detection using DAR
neutrino beam at J-PARC MLF(2022)

1 kg LOCOND
prototypeSterile Neutrino Search at
JSNS2

Sterile Neutrino
Sterile neutrino : insight for the questions beyond the SM(e.g. PLB 631, 151 (2005))- No strong, EM and weak interactions- Introduced to explain both results of LSND and LEP- Maybe recognized by neutrino oscillations- Could be right-handed neutrino or new particle- Beyond the PMNS standard oscillation- Indicated by LSND, MiniBooNE, reactor anomaly, andGa experiment

Sterile neutrino can be also one of the Dark Mattercandidate?

Hints for Sterile Neutrino (Dm2 ~ 1 eV2)
▪ Anomalies that cannot be explained by standard neutrino
oscillations for ~20 years
Experiments

Neutrino source

signalsignificanceE(MeV),L(m)LSND

m Decay-At-Rest

nm → ne

3.8s

40,30

MiniBooNE

p Decay-In-Flight

nm → ne

4.5s

800,600

nm → ne2.8s

combined

4.8s

Ga (calibration)e capturene → nx

2.7s<3,10Reactors

Beta decay

ne → nx

3.0s

3,10-100→ Excess or deficit does really exist?
→ A new oscillation between active and inactive(sterile) neutrinos?
→ However, no indication for nm → nm and negative results fromrecent reactor measurements using energy spectra

LSND nm → ne Signal
1998 at LANLLSND Results and Allowed Region
1998(1990-1995, 1997-1999)

MiniBooNE Latest Results• Significant excess of low energy
events : 4.5 s• The excess is claimed due to thesame oscillation observed by theLSND.
• Concerns on systematic uncertainties
of neutrino interactions andbackground understanding• MicroBooNE can check the excess
due to the gamma rays or electron
antineutrinos

Sterile Neutrino Oscillation

Yufeng LiRENOMicheleMaltoni

Sterile Neutrino Oscillation
Null results ofdisappearance

2021
2020

Future Sterile Neutrino Search(Reactor disappearance)

Yufeng Li

Future Sterile Neutrino Search

Yufeng Li

JSNS2 Experiment(J-PARC Sterile Neutrino Searchat J-PARC Spallation Neutron Source)JSNS2 Collaboration
JAEA
KEK
Kitasato
Kyoto
Osaka
TohokuSoongsilDongshin
GIST
Seoyeong
Chonnam
Seoul

Chonbuk
Kyungpook
Sungkyunkwan
Seoul Sci Tech

Alabama
BNL
FloridaMichigan

SussexImproved Search at JSNS2▪ Direct test of the LSND with better sensitivity- Muon antineutrino beam from muon Decay At Rest (DAR)▪ Narrow (~9 ms) pulsed (every 40 ms) neutrino beam at JPARC MLF :(vs. continuous beam used by LSND)- Pure muon decay at rest
- Narrow timing window for cosmic ray rejection- No decay-in-flight source- No beam induced fast neutrons- The neutrino energy spectrum is perfectly known- The neutrino beam already available▪ Improved detector :- Gd doped LS→ significant reduction of backgrounds by a tighter (~1/6)
time coincidence and a higher (2.2 → 8 MeV) delayedenergy + well-known cross section of IBD

JSNS2: J-PARC E56
Sterile n search@MLF

400MeV

J-PARC Facility(KEK/JAEA）
South to North

http://research.kek.jp/group/mlfnu/eng

3 GeV RCSNeutrino Beams(to Kamioka)

25Hz, 1MW (design)

Materials and Life
Science Experimental
Facility (MLF)

CY2007 Beams
JFY2008 Beams
JFY2009 Beams

Hadron hall
Bird’s eye photo in January of 2008

JSNS2 at J-PARC MLF

MLF building (bird’s view)

Detector @ 3rd floor(24m from target)

Hg target = Neutron
and Neutrino source

50t liquid scintillator detector(17t Gd-loaded LS in target)(4.6m diameter x 4.0m height)~120 10” PMTs

3GeV pulsed proton
beam

Searching for neutrino oscillation : nm → ne with baseline of 24m.
no new beamline, no new buildings are needed → quick start-up

Neutrino Source: Mercury Target at MLF▪ World-class high intensity neutron source driven byhigh power proton beam
- beam energy: 3 GeV- design beam power: 1 MW

Timing and Energy of Neutrino Beam
• Timing: Ultra-pure n from m+ Decayat-Rest by a pulsed neutrino beam

➢ Removal of n from p and K with beamtiming➢ Removal of beam fast neutrons w/ time
➢ Reduction of cosmic BKG by 9ms time
window.

➢ Energy: Good for signal BKG
separation➢ Well-known spectrum of n from m➢ Easy energy reconstruction of IBD.
(En ~ Evis + 0.8MeV)➢ Highly suppressed n from m-Signal Extraction & Sensitivity

3 years x MW x 17 tons
x 50 tons

Schedule for Detector Construction
2018
2018
7-9

201910-12

2019
1-3

2020
4-6

7-9

10-12

2020
1-3

Acrylic vessel
production
Acrylic vessel
installationLS
production
PMT
installation
Dry runFillingFirst physics
run

Major Korean contribution

4-6

7-9

10-12

Construction of Acrylic Vessel

Relocated SUS Tank (Mar. 14, 2018)

SUS Tank and Acrylic Vessel at J-PARC

PMT Installation▪

105 PMTs from RENO, Korea
23 PMTs from DC, Japan▪

33 PMTs installed and ~40 will
be installed till Oct. 2019.

▪

50 more PMTs will arrive
before Dec. 2019.

Liquid Scintillator by Korean GroupSummary• Confirming or refuting existence of “sterile neutrino oscillation”
results has been one of the hottest topics in the neutrino
physics in the last two decades.
• The JSNS2 experiment will begin data taking in early 2020 andprovide an ultimate test of the LSND anomaly without any
ambiguity.
• If sterile neutrino oscillation is indeed found, it will be a big
discovery of a dark matter candidate.

• The Korean group has been actively participating in thedetector construction including delivering 36 tons of liquid
scintillator and ~100 10-inch PMTs. We expect to play animportant role in obtaining results.

Thanks for your attention!

Backup Slides

Efficient Search for Neutrino Electromagnetic Property▪ Change of CEvNS cross section at low energies due to neutrino magneticmoment

Compact Neutrino Telescope▪ Development of CEvNS telescope to detect an intense neutrino burst fromSupernova

IceCUBE25M ton water42m

C Scentific American

Super-Kamiokande50k ton water39m

CEvNS Solar Neutrino Detection▪ Solar neutrino detection with a compact detector due to enhanced
CEvNS cross section

n+N→n+N

CONUS Detector

Plastic Scintillator for PSD
Development of plastic scintillator providing pulse shape discrimination(PSD) between neutron and gamma by Eljen & LLNL

Upgraded plastic scintillator
showing PSD performance similar
to scintillator EJ-309

Neutrinos from Muon Decay At Rest (DAR)

(1)
(3)
(2)

μs

Expected Signal and Background