Review of Accelerator based
Short-Baseline Neutrino oscillation
searches
DBD23
International Workshop on “Double Beta Decay and Underground Science”
Dec 1st-3rd, 2023

Dongha Lee, KEK
1

Indication of a sterile neutrino
Anomalies, which cannot be explained by standard neutrino oscillations
for a few tens years are shown.
Experiments

Neutrino source

signalLSNDµ Decay-At-Restνµ ! νe

3.8σ

40,30

MiniBooNE

π Decay-In-Flight

νµ !

νe

4.5σ

800,600

νµ ! νe2.8σ

combined

4.7σ

Dongha Lee

significance E(MeV),L(m)BEST (Ga)e capture

νe !

νx

∼4.0σ

<3,10

Reactors

Beta decay

νe !

νx

3.0σ

3,10-1002

Phys.Rev.D64:112007 (2001)

μ DAR

LSND
3.8sigmaν̄e excess

π DIF

PRL 121, 221801

Dongha Lee

MiniBooNE
4.5sigmaνe excess3

Short-Baseline Neutrino (SBN) program
Booster Neutrino
Beam (BNB)ICARUS
476tonLArTPCOperation
2022 Summer~

Dongha Lee

MicroBooNE
89ton
LArTPC
Data taking
2015-2021

8GeV protons

Near Detector
112tonLArTPC
Anticipate
to begin2023~
4

MicroBooNE results so far- They put 89t fiducial LAr detector
at the neighborhood site of MiniBooNE- Data taking 2015-2021- eLEE search=> No excess is observed (right plots)- 3+1 Oscillation Analysis=> Exclude part of LSND allowed region (below plots)

Dongha Lee

Phys. Rev. Lett. 130.011801

Phys. Rev. Lett. 128. 241801

5

Status of ICARUS- ~600m from BNB,
476ton LArTPC- First detector operation :2022 Summer~
Eur.Phys.J.C 83 (2023) 6, 467- Initial data has been used to perform detector physics
measurements relevant for future LArTPC experimentsCollected POT

Dongha Lee- Joint analysis forneutrino oscillation
with SBND andMicroBooNE
will be performed

62
2
JSNS / JSNS -II Experiments

Direct test of LSND
Collaboration meeting @ J-PARC (2020/Feb)

JSNS2 collaboration (~60 collaborators)- 7 Japanese institutions (27 members)- 10 Korean institutions (25 members)- 1 UK institution (1 member)- 3 US institutions (5 members)- 1 China institution (3 members)

JAEA
KEK
Kitasato
Kyoto Sangyo
Osaka
TohokuTsukuba

Dongha Lee

Chonnam National
Jeonbuk National
Dongshin
GIST
Kyungbook
Kyung Hee
Seoyeong
SoongsilSungkyunkwan
Seoul National ofsci and tech

BNL
FloridaMichigan
Utah

SussexSun Yat-sen(Zhongshan)

Spokesperson: T.Maruyama (KEK)
Co-spokesperson: S.B.Kim (Sun Yat-sen)7

Indication of a sterile neutrino
Anomalies, which cannot be explained by standard neutrino oscillations
for a few tens years are shown.
Experiments

Neutrino source

signalsignificance E(MeV),L(m)LSNDµ Decay-At-Restνµ ! νe

3.8σ

40,30

MiniBooNE

π Decay-In-Flight

νµ !

νe

4.5σ

800,600

νµ ! νe2.8σ

combined

4.7σ

We aim tohave a direct
test for thisBEST (Ga)e capture

νe !

νx

∼4.0σ

<3,10

Reactors

Beta decay

νe !

νx

3.0σ

3,10-100

JSNS2 uses the same neutron source(μ), target(H) and the detection principle (IBD) as the LSND.
=> Even if the excess is not due to the oscillation, we can catch this directly.
=> Two advantages : short-pulsed beam / Gd-LS give excellent S/N ratio.
Dongha Lee

8

JSNS2: J-PARC E56
2
JSNS -II: E82
400MeV
Sterile ν search@MLF
I'J9K''%&CC<>-;'-<'D<5-;!"#$%&'()*+,+-.
/0102!$1$3

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

D9>-5+=<'49)E8F/-<'0)E+<G)H

25Hz, 1MW (design)

IAJ
9K'
L%

L)-95+),8')=6'N+?9'
C*+9=*9'1O:95+E9=-),'()*+,+-.'/LN(H

Low duty factor
beam(short pulse +small
repetition rate)
gives
excellent S/N ratio.

M)65<=';),,

Dongha Lee

4+5678'9.9':;<-<'+='!)=>)5.'<?'@AAB

9

JSNS2 / JSNS2-II : Sterile Neutrino Search
MLF building (bird’s view)

Near detector@ 3F(24m from Hg target)

Hg target = neutronand neutrino source

Nucl. Inst. Meth. A
1014 (2021) 165742(JSNS2-I,ㅤJSNS2-II near detector
17t GdLS fiducial (target)(4.6m diameter x
4.0m height, 120 10” PMTs)

Far detector @Outside of MLF(48m from Hg target)

3GeV shortpulsed beam

Searching for neutrino oscillation : νµ ! νe withbaseline of 24m (near), and 48m (far detector)(JSNS2-II:

Dongha Lee

Far detector)
32t GdLS(6.2m dia x
6.2m (h)~228 10”
PMTs)

Current JSNS2

Globalfit indicated region
M. Dentler,etal., JHEP08010 (2018)

JSNS2-IICovers theglobal fit indicatedregion nicely.

JSNS2-I : 1MW x 3years (near only)- commissioning (2020) :Eur. Phys. J. C (2022) 82:331- 1st/2nd/3rd long physics run(2021,2022,2023)-> Smooth data taking- 4th long physics run
will be started from 2023 Dec
JSNS2-II : 1MW x 5years(near + far)
- Proposal (2020) :arXiv:2012.10807- New far detector :32tons, 48m baseline- Two detectors with di erent
baselines-> Good sensitivity on low Δm2
region (a solid conclusion on
LSND anomaly)- J-PARC/KEK granted10
the stage-2 (out of 2) status

Strategy to search a sterile neutrino
TimingSterile neutrino oscillation during 24m,48m baseline.
PromptDetection by coincidence of IBD (Inverse Beta Decay)
Delayed-> Prompt : e+ signal-> Delayed : gammas from neutron capture on gadolinium (Gd)

2 ~10μs frombeam
ΔTp-d <100μs

Energy20~60 MeV
7~12 MeV+ Spatial correlation cut
ΔVTXp-d < 60cm

νs ?

,48m

fi

Dongha Lee

Liquidscintillator
is lled in thedetector

11

Operation of Near Detector
Hourly delivered POT- Beam Power is 950kW from 2023 Springat exit point of RCS (design : 1MW)

1stphysicsrun

0.74MW

0.84MW

3rd
physicsrun

0.62MW- Smooth data taking so far- There is an accelerator maintenancein summer every year

2nd
physicsrun

Accelerator
MaintenanceIntegrated POT
Web-monitoringis performed
as real-time!!!

Fast Neutrons
rates vs time
Dongha Lee

Michel electrons
rates vs time

Delivered POT so far : 3.28x1022(28.7% of approved POT(3y) for JSNS2)

12

252Cf 3D calibration : Study of Energy/Vertex reconstruction
252Cfradioactive source

Vertex Y
Data taking @ R~1.5m(Target Size is up-to
R~1.6m)Vertex X
Dongha Lee(NEW) 252Cf 3D calibration system-> Any of position (R&Z) can be covered!!!
Reconstruction Parameters were studied based on this calibration=> Reconstruction performances were checked using several data sample

Calibration using 252Cf and Michel electrons are crucial!!!

13

Energy/Vertex reconstruction performance
Energy/Vertex
reconstruction
performances
are good(in ducial)
True vertex vsreconstructed vertex(z-direction)

Reconstructed energyof n-Gd captured events

8MeV

Reconstructed energy spectra ofMichel electrons at each positionZ ~ 1.0m

True vertex vsreconstructed vertex(r-direction)fi

Z ~ -1.0m

R ~1.4m
14

Blind analysis and Side-band study

15

Toward the sterile neutrino search (Blind analysis)- We are doing the blind analysis tosearch a sterile neutrino.
- All energy side-bands
should be understood
before opening the signal region.

Other Main Bkgs−

ν̄e from μ :PE ~60MeV
CNgs :
PE ~40MeV- Side-bands are de ned by energies
like right plot.
- The rates in the side-band regions will
be predicted by thecontrol samples driven by datafi

- Now, side-band 4 (prompt 60-100MeV)
data are opened!!!

Cosmic fast neutrons,
Accidentals
are main backgrounds

16The first comparison between the observation vs expectation~Side-band4 (prompt 60-100MeV)~ 1
Prompt E

Delayed E

JSN

S2 p

relim

inar

y

dT
Dongha Lee

Before applying
Spatial correlation ΔVTXp-d < 60cm

dVtx

Total
Neutrons
Accidental

Observed
events1498+- 38.7

Expectation
events1528.5+- 5.91421.7 +- 5.7
106.8 +- 1.5- The observed events are comparedwith the background expectations(Cosmic fast Neutrons + Accidental)=> well agreed.
=> Cosmic fast neutrons background isdominated.
=> Pulse Shape Discrimination(PSD)
would reject them. (Goal : 99% rejection)=> Study is on-going.
=> After applying PSD,
the accidental will be dominated.
=> Understanding of accidental is much
arXiv 2308.02722
improved recently.
17

Study on the fast neutron background - PSD- Fast neutrons can mimic the IBD signals
from electron anti-neutrino.
- Those two will be separated by the PSD
method.
=> using the neutron-like/electron-like
templates (averaged waveforms from data).

Separation by
Likelihood

Averaged
waveforms

Separation by
Convolution
Neural Network
Dongha Lee- Both of Likelihood team /Machine-learning(CNN)
team work independently.
=> progress is on-going.

(Goal : 99% rejection of fast neutrons)18Study on the accidental background - 1
125μs time window triggered data
(special calibration run)arXiv 2308.02722
Prompt timing ;energy spectrum

promptDelayed timing ;energy spectrum

delayed125μs fully covers
the timing structure for IBD

Rp = (2.20 ± 0.09) × 10 /spill- The single rates of the prompt / delayed timing region were
understood using 125μs time window special calibration data
- The prediction of the accidental background rateis calculated with multiplying these single rates.

−4

−2
±
Rd = (1.80 0.01) × 10 /spill

Racci = Rp × Rd × εcut
εtiming likelihood = 46 %Dongha LeeεΔVTX = 5.1 ± 0.1 %19Study on the accidental background - 2
125μs time window triggered data
(special calibration run)arXiv 2308.02722
Prompt timing ;energy spectrum

promptdelayed125μs fully covers
the timing structure for IBD

x

Rp = (2.20 ± 0.09) × 10 /spill- The single rates of the prompt / delayed timing region were
understood using 125μs time window special calibration data
−4

- The prediction of the accidental background rateis calculated with multiplying these single rates.

Racci = Rp × Rd × εcut
Dongha LeeεΔVTX = 5.1 ± 0.1 %(ΔVTX cut will be explained in next page)

Delayed timing ;energy spectrum−2±
Rd = (1.80 0.01) × 10 /spill=

Racci = (9.29 ± 0.42) × 10
/spill /0.75MW−8(Expected IBD signal is 4.59 x 10-8 /spill/MW=>comparable)
20

Study on the accidental background - 3
arXiv 2308.02722- Mimic IBD pair using prompt / delayed eventsat the di erent spills [Spill-shift method]=> 1, 2, 3 … 10000th shifted spills=> Accidental background control sample- This method will be used for signals/side-bands
ff

Dongha LeeεΔVTX = 5.1 ± 0.1 %To reject accidental backgrounds,
ΔVTXp-d < 60cm is applied.
=> Side-band 4 is checked again.
21

The first comparison between the observation vs expectation~Side-band4 (prompt 60-100MeV)~ 2
After applying
Spatial correlation ΔVTXp-d < 60cm

Before applying
Spatial correlation ΔVTXp-d < 60cm

JSN

S2 p

relim

inar
y

Observed events

Expectation events

No ΔVTXp-d Cut

1498 +- 38.7

1528.5 +- 5.9

ΔVTXp-d < 60cm

983 +- 31.4

988.4 +- 3.2

Dongha Lee

ΔVTXp-d < 60cm

Neutrons 982.8 + Accidental 5.6
If PSD is applied, Neutrons ~10 events- The number of events
for the observed &the expectations
have good consistency,
for both of
the spatial correlation
condition cases.
22

2
JSNS -II (2nd phase)- New Far detector=> Fiducial volume 32ton(37m3) and 48m baseline.
=> 150m3 for veto & Gamma-catcher.
=> 172(inner)+48(veto) PMTs.
=> Outside of MLF building.
- Two detectors (Near + Far) with two di erent baselines=> The sensitivity at low Δm2 region is much improved
compared with only single 24m detector.
=> A sold conclusion on LSND anomaly.
- The construction work is being progressed rapidly.

JSNS2 3years +JSNS2-II 5 years
23

ff

Dongha Lee

ⓒKEK (IPNS)

arXiv 2309.01887
accepted by JINST- The construction of thestainless steal tanks wasnished (2023 Mar)
Dongha Lee
fi

fi

2
JSNS -II (2nd phase) - construction- The acrylic tank was made by
Taiwan company.
- The transmittance of the acrylic=> ~93% @ 400~600nm.

- 190 PMTs were donated from Double-Chooz.
- Installation of 172 PMTs for inner detector
is nished!!!
- The calibration system was installed.
-> LED / Temperature sensors
24

2
Schedule of JSNS -II
2021
1-3
s.s.tank

4-6

2022

7-9

10-12

1-3

bid

construction

Acrylic
vessel

2023

4-6

7-9

bid

construction

10-12

1-3

4-6

7-9

Transp.

Installation (inner)

PMTs
DC dismantle/ shipping (190PMTs)(Gd)LS

donation

2024
10-12

1-3

4-6

7-9

10-12

installation
Installation (veto)
shipping (30PMTs)

Storage / keep

electronics

Delivery
Filling
Data taking

Dongha Lee

Final step of the construction-> Close to data taking!!!

25

Summary- There have been 1st (2021), 2nd (2022) and 3rd (2023) long physics run.
(JSNS2 single 24m detector)- Analyses are on-going with the data.
=> 252Cf 3D calibration is developed.
-> Good reconstruction performances in ducial volume.
=> One side-band (prompt 60-100MeV) data are opened !!!
-> Has been studying fast neutron background (with PSD).
-> Study on the accidental background (using single rates).
Accidental study
arXiv 2308.02722 / submitted to EPJC

- JSNS2-II (2nd phase) with new far detector (48m, 32tons of GdLS)
Acrylic tank :-> Construction works are on-going rapidly. arXiv 2309.01887
accepted by JINST-> Plan to data taking in next year.
26
fiDongha LeeBACKUP

Dongha Lee

27

First comparison of the observed vs expected events~Side-band4 (prompt 60-100MeV)~ 1
Prompt E

Delayed E

JSN

S2 p

relim

inar

y

dT
Dongha Lee

After applying
Spatial correlation ΔVTXp-d < 60cm

dVtx

Total
Neutrons
Accidental

Observed
events983+- 31.4

Expectation
events988.4+- 3.2982.8 +- 3.2
5.6 +- 0.1- The observed events are comparedwith the background expectations(Cosmic fast Neutrons + Accidental)=> well agreed.
=> Cosmic fast neutrons background isdominated.
=> Pulse Shape Discrimination(PSD)
would reject them. (Goal : 99% rejection)=> Study is on-going.
=> After applying PSD,
the accidental will be dominated.
=> Understanding of accidental is much
arXiv 2308.02722
improved recently.
28

Expected visible energy and Sensitivity (1st phase)- Expected signals/bkgs for only single 24m
detector (JSNS2 TDR, arXiv:1705.08629)- Spectral t is sensitive
to the di erence of energy spectrum

1M x 3years
Globalfit indicated region
M. Dentler,etal., JHEP08010 (2018)

29
fi

ff

Dongha Lee