Takasumi Maruyama (KEK)

Caveat: there are many experimental
results so far. I cannot cover all of them.
1 Sterile

neutrinos could give an insight for
the questions beyond the standard model.
 Nostrong, electro-magnetic, weak interactions.
 Introduced to explain both results of LSND and LEP
experiments.
 Observed by mainly neutrino oscillations
 Could be nR (Majorana) or new particle
 Oscillated by the beyond PMNS matrix.
 LSND, MiniBooNE, reactors, Ga (and BEST)
experiments indicate the existence.

3•Anomalies, which cannot be explained by standard neutrino
oscillations for ~20 years are shown;
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

4.7s

MicroBooNE had new results
Ga (calibration)e capturene → nx

2.7s<3,10Reactors

Beta decay

ne → nx

3.0s

3,10-100BEST had new results•••

Excess or deficit do really exist?
The new oscillation between active and inactive (sterile)
neutrinos?
4Direct tests are being examined for the anomalies.

LSND (appearance)

1998 at LANL
LSND

mc43e Signal

600ms 120Hz
target+beam stop
configuration
DIF, n bkg.
p → m + nm
m→ e + ne + nm

² + # m +! m nee +! e! mOscillations?

!ep-, m-LSND
absorbed
before decayn’s
in conjunction
with theinto
atmospheric
and-4
there solar
shouldnot beresults
ne atneeds
the level
7x10
oscillation
moreofthan
3 n’sÞ Models developed with 1 or 2 sterile n’s

Signal : ne p→e+n

np→d g(2.2MeV)

Saw an excess of:
87.9 ± 22.4 ± 6.0 events.
With an oscillation probability of(0.264 ± 0.067 ± 0.045)%.
3.8 s evidence for oscillation.

A direct test is being done by JSNS2/JSNS2-II.
See pages later.

MiniBooNE results
8GeV
fromFNAL Booster

Mineral oil
Cherenkov• Significant low energy events excess is observed. (4.5 s)• They claimed that this excess is due to the same
phenomena as LSND experiment.
• Concerns are– Systematic uncertainties (neutrino interactions, backgroundunderstandings)• MicroBooNE is checking the results. See next page.
– LArTPC can distinguish gammas and electrons.

Neutrino2018
En-Chuan Huang

170t LAr detector at
the neighborhood siteof MiniBooNE withbetter electron PID.
No observation of similar low
energy electron excess (eLEE) tothe MiniBooNE (right plots).
MiniBooNE and MicroBooNE need tocheck their results each other.

Hanyu Wei’s talk in
Neutrino 2022

Daya-Bay

Daya-Bay experiment(reactor + liquid
scintillator detector)
pointed out thatneutrino flux from 235U
has smaller flux thanthe prediction,especially.
 BEST experiment

A 3.414-MCi 51Cr ne source
was placed at the center oftwo nested Ga volumes
 They observed 20-24%
deficit of the ne rates.
 They claimed that the results
are consistent with theprevious measurements.
(>5s significance)
BESTP(ne→ne)ne disappearance
by reactor
experiments

Dm2>0.1, sin22q>0.05 → Losc = [1-10] m
10110

102

103

104

L (m)

STEREO(arXiv:1912.06582)

Neutrino-4 has an interesting
results.

DANSS(Neutrino 2020)

PROSPECTS(Neutrino 2020)

Neutrino-4(Neutrino 2020)

ClaimedOscillation
w/ (Dm2,sin22q)=(7.0eV2, 0.4)

Georgia Karagiorgi, Columbia Univ.
(NuFact2022 talk)Current situation / what to do• Currently, 3+1 oscillation model cannot explain all experimental results.
– I didn’t cover at all, but nm→nm disappearance is not seen. (e.g.: OPERA, NOvA,T2K, MINOS/MINOS+, MicroBooNE, Super-K, IceCube, ..)• Results of the LSND, MiniBooNE, BEST experiments have crucial
significance, thus it is time to test their results directly under thissituation. (with improved methodologies)• The direct tests are being and will be examined by experimentalists.
– MicroBooNE (results are being shown) / SBN (SBND+MicroBooNE+ICARUS) for
MiniBooNE anomaly. → MicroBooNE has results, and further investigation willbe done.
– JSNS2 / JSNS2-II check the LSND anomaly directly.
– How to interpret the BEST experiment? Other direct test?
– Many reactor experiments are on-going, and they can check further.

Peter Wilson’s talk @ WINP workshop

3 LArTPC detectors(100-600tons)

Liquid Argon TPC

Ionization electrons• Principle

ElectricField– Quasi-free electrons from ionized tracks aredrifted.

Cherenkov light• Charge (MIP)〜1fC/mm (~5500e/mm)• drift velocity = 2m/ms @ 1kV/cm– Position information from2D (x,y) anode andtiming → 3D tracking w/ 1mm resol.
– No amplification from LAr (different from Gas Ar)

Chargedparticle• Features– LAr is cheap and high density material– LAr TPC has high tracking efficiency– Low energy threshold– PID by local dE/dx (each wire or strip)– Full sampling and homogeneous calorimeter• Advantages for physics– Multi-track meas. -> exclusive meas,– Calorimetric energy measurement. (elastic events
selection is unneeded.)– Good e/p0 separation

Scintillation lightpion

40 cm
positronproton

Test-Beam
0.8 GeV/c
76 cm

data

Compared to MiniBooNE,
there is no p0 background
eventsAs shown in former of theslide, MicroBooNE showed
the first results.
ICARUS is now running.
SBND is being constructed.

Takasumi Maruyama (KEK)

Direct test of LSND.

Collaboration meeting @ J-PARC (2020/Feb)

JSNS2 collaboration (61 collaborators)- 6 Japanese institutions (29 members)- 10 Korean institutions (24 members)- 1 UK institution (1 member)- 4 US institutions (7 members)

JAEA
KEKKitasato
Kyoto
OsakaTohoku

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

BNL
FloridaMichigan
Utah

SussexSpokesperson: T.Maruyama (KEK)
Co-spokesperson: S.B.Kim (SKKU)

•••Anomalies, which cannot be explained by standard neutrino
oscillations for ~20 years are shown;
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

4.7s

Ga (calibration)e capturene → nx

2.7s<3,10Reactors

Beta decay

ne → nx

3.0s

3,10-100
We aim tohave a direct
test for thisExcess or deficit do really exist?
Note: JSNS2 uses the same neutrino source (m), target (H) anddetection principle (IBD:ne+p→e++p) as the LSND → even if
this is not due to the oscillation, we can catch this directly17JSNS2: J-PARC E56
JSNS2-II: E82
400MeV
Sterile n search@MLF
3 GeV RCS

J-PARC Facility(KEK/JAEA）
South to North
Low duty factor beam(short pulse + low
repetition rate)
gives excellent S/N ratio.

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

Neutrino Beams (toKamioka)

25Hz, 1MW (design)

Materials and Life
Science Experimental
Facility (MLF)

Hadron hall

Bird’s eye photo in January of 2008

0.6MW (Jan/12 – Apr/5 2021)
0.7MW (Apr/5 – June/22 2021)
0.7MW (Jan/29 – Apr/5)
0.8MW (Apr/7 – May/31)
beam were utilized for JSNS2.
→ Next beam
- starting from 0.8 MW- electricity costs affect to theavailable beam time afterNov.

MLF building (bird’s view)(JSNS2):1 MW x 3 y(near only)••

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

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

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

3GeV shortpulsed beamSearching for neutrino oscillation : nm → ne withbaseline of 24 m (near), and 48 m (far detector)(JSNS2-II:Far detector)
32 t GdLS(6.2 m dia x
6.2 m (h)228 10”PMTs)

Current JSNS2

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

JSNS2-IICovers theglobal fit indicatedregion nicely.

•Commissioning (2020)
First long physics run (2021)• Smooth data taking (0.5 years)• Beam Power: 600-700kW
Second long physics run (2022)• End of Jan to end of May• Beam power : 700-800kW
2.52x1022POT can be used for analysis(JSNS2-II):1 MW x 5 y• Proposed in 2020 (arXiv:2012.10807)• New far detector:
fiducial 32 tonnes and48 m location.
• Good sensitivity on low
Dm2 region.
• Two detectors with two
different baselines -> asolid conclusion on LSNDanomaly.
• J-PARC/KEK granted thestage-2 approval.
• The construction isbeing progressed rapidly.

Side-bands defined by energies of IBD
candidates will be checked before opening
the signal region.
 The rates in the side-band regions will bepredicted by the self-triggered data (forneutron background induced by cosmic rays),
the kicker triggered data (for theaccidental background), and sterile delayedtrigger.
 After application of PSD, region 1,2,3,4
will be dominated by accidental.
 If the rates in the side-band regions arematched with the prediction well (withinstat + syst. uncertainties), we will open
the signal region

Energy of IBD delayed candidate (MeV)Start tocheck
Side band1(dominatedby accidental
BKG)

12Side band3(dominatedby neutronBKG)
7signalSide band4(dominatedby neutron
BKG)

Side band2(dominatedby neutron
Start to BKG) → nearchecksignal region
2060
Energy of IBD prompt candidate (MeV)• Some of side band
regions are being
checked now20

Single rate of the sterile prompt
Muons are rejected by veto region.
 Michel e is rejected by vetoactivities of 10us from the inner
region activities.
 Fiducial cut (R<1400 && |Z|<1000mm)
 Each component are estimated by energy
spectra.
JSNS2 TDR : 3.8x10-4/spill (9us)component

Remaining Rate (Hz)after selection
criteriaCosmic fast n

3.9+-0.7

Michel e

13.3+-0.3

Cosmic gammas

9.3+-0.6

Total

26.8+-0.1

Rate/spill(8ms)(2.14+-0.04)x10-4

PSD improvement(R<1400 && |Z|<1000mm)

21Monochromatic energy nm fromK+ Decay-At-Rest (KDAR)

KDAR n prompt signal energy

Data:(high purity
clear peakis seen)• K+ decay-at-rest (KDAR) at the mercury target(236MeV nm)• MLF gives nice environment to measure the KDAR n– Clear and high purity signal is seen. (top-right)– Currently, no systematic uncertainties for energy scale areassigned. No cross section measurements either.
– Hereafter, the nice feed-backs to understand the quasi-elastic
nm interaction will be anticipated.
n energy from K+ DAR (Km2): monochromatic
Inside liquid scintillatornm

Mercury
Targetµ+neneScintillation light(prompt)

24 m

nm

K+

µNo oscillatrion
Monochromaticenergy
nm

Message: DAR n is seen
→ n beam and detector work wellneutronprotonelectron(From µ decay)
Scintillation light(delayed)

Scintillation light(prompt)

Protonbeam~20m
Detector
location~30mBaseline is ~48m.
~Twice fiducial masscompared to 1st detector.
No detector buildings.
MLF approved to use
23
this space.

 Design:

almost identicalto the existing neardetector.
m3 Gd-LS for the neutrino
target 150 m3 no Gd-loaded LS forthe veto and gamma catcher.
Linear AlkylBenzene (LAB)
based Liquid scintillator.
 228 PMTs will be used 37

 Going

well. See slides later.

Inner s.s. tank (GC)

Outer s.s. tank (veto)in the "roofspace" with air
conditioner to keep
18-28 C Construction Status:

Spill tank

 Electronics

Roof space

Acrylic tank(Gd-LS 32tons)

24Cleanup of spill tankOuter s.s. tank is installed into the spill tankOuter s.s. tank is installed into the spill tank(14-Mar)(14-Mar)Movement of the top-lid of the outer s.s. tank (14-Mar)

the installation of the inner s.s. tank (15-Mar)

the installation of the inner s.s. tank (15-Mar)25

• 190 PMTs arrived at J-PARC on 27-June in 2022 (from Paris)→ JSNS2-II appreciates to Double-Chooz experiment→ will be installed to the inner s.s. tank soon.
• Dismantling the DC PMT jigs structure has finished.
• Dead PMTs checks have been done.

Dismantling
DC PMT jig structure

190 PMTs arrival(from Paris to J-PARC)

Dead PMT checks• Following the original schedule even under the COVID-19.
• PMT: Double-Chooz donated 190 PMTs and will donate 30 PMTs. Installation will be done soon

Sterile neutrinos are one of the hottest topics in neutrino field.
Many experiments are on-going to confirm or refute the existence.
 Significant

anomalies coming from LSND, MiniBooNE and BEST.
 The direct tests (confirming or refuting) of these results are essential.
 MicroBooNE / SBN will make a direct test for MiniBooNE.
JSNS2 and JSNS2-II aim to test the LSND anomaly directly.
use the same neutrino source (muon), target (H) and detection principle (IBD),
but much smaller accidental background due to Gd-loaded LS and low duty factor
J-PARC MLF beam.
started data taking from 2021-Jan (2.52 x 1022 POT so far).


JSNS2-II has good progress.

The sensitivity for the sterile neutrino search (especially, in the low Dm2region) are improved a lot.
 Stage-2 (out of 2) was granted by J-PARC / KEK officially.
 Daya-Bay donated the GdLS / LS for JSNS2-II. (now they are in Japan)
 The stainless steel tank was completed.
 PMTs are donated by Double-Chooz, and will be installed soon.
 Aim to start the JSNS2-II from 2023.
29

Production / Detection• Large amount of parent m+ in Hg target → nm are produced.
• If sterile n exist, nm → ne oscillation occurs with 24m.
• Oscillated ne is detected by Inverse Beta Decay (IBD): ne + p → e+ + n w/ wellestablished detector technique

3GeV
pulsedprotonbeam

Most of them
are same as
the LSND.
→ Direct ultimate
tests for LSND.

(Decay-at-Rest)
Scintillation lightp+

IBD criteria

TimingEnergy

Prompt1<Tp<10μs

20<E<60MeV

DelayedTp<Td<100μs

7<E<12MeV<T>~30ms

Scintillation light(~ 8MeV In total)

But use muchbetter beam and
Gd loaded LS.
→ Much better
S/N→ Much bettersystematics
30JSNS2

LSND

Target Mass

17 tons

167 tons

Baseline

24 meters

30 meters

Beam energy

3 GeV (larger # p+ but also p-)

0.8 GeV

Beam Duty Factor

0.8/40000 (by Synchrotron)

1/14 (by Linac)

Stopping m-/m+

1.7 x 10-3

6.5 x 10-4

Liquid Scintillator

Gd-loaded + large scint. light

Small #scinti. Light (to see
Cherenkov), no Gd

Delayed signal

Etot~8MeV, Dt~30ms

Etot~2.2MeV, Dt~200ms

DE/E

2.4% @ 45MeV

7% @ 45MeV

Fast neutron rejection

Pulse Shape Discrimination

Cherenkov# of IBD signal events(after offline cuts)~20 events / year

15 / year(LSND best fit (Dm2=1.2eV2, sin22q=0.003))

Left: Energy spectrum; （Top: Dm2=2.5eV2,Bottom; 1.2eV2 sin22q = 0.003)
 Right: Sensitivity of 3 years physics runningof JSNS2 with one detector.
JSNS2 best case

JSNS2ExploringRegion(90%)

LSND best fit

S. Ajimura et al.
arXiv:1705.08629

9990

MW x 3 years(x 1 detector)

32

Detector construction (2017-2020)• The detector construction wasfinished 2020-Feb.

• Stainless steel tank was produced by
Japanese company (2017-2018:Morimatsu) JINST 14 (2019) no.09, T09001• Acrylic tank was produced by Taiwancompany (2018-2019: Nakano).
• 10” PMTs : arXiv:2005.01599 (also accepted by JINST)• ~53% is reused from RENO.
• ~30% is newly purchased.
• ~17% is reused from Double-Chooz.

catcher vetotarget• 35 ton of pure liquid scintillator wasproduced by Korean collaborators at
RENO site (2018) JINST 14 (2019) no.09, T09010• 17 tons Gd loaded liquid scintillator
was donated by Daya-Bay (2019).
• Electronics and DAQ system: arXiv:2006.00670••••

FADCs are donated by DC – Japan.
Front End Elec. are donated by DC.
HV are reused from DC.
Elec. upgrade will be done (See backup)• New Fast LED calibration system

Very efficient experiment using reused or
donated materials from various experiments.
We do appreciate Daya-Bay, RENO and DC.

See also posters #353, 355, 444

Fast Neutrons are severe backgroundbecause it is “correlated” BKG.
Pulse Shape Discrimination separates
the IBD signals and fast neutrons.
Cosmic ray muonsConcrete, Iron, etc
Average Waveform (Data)
Difference of IBD promptRegion (20<E<60MeV)

Gd loaded LSpnn thermalized
pn Gd

Capturegammas

Recoil proton; 20-60MeV(mimics IBD prompt)• We are trying a few methods to distinguishthese waveforms.
• Likelihood / machine learning methods indicatethat we can achieve the TDR rejection factor
of fast n (~100).
34• See next page.

Selection of KDAR signal
ΔVTX vs KDAR Prompt Evis
Accidental BKG

Correlated BKGSignal•

KDAR signals and BKGs can be well separated by using ΔVTX(spatial correlation between prompt and delayed).
-> Correlated BKG (cosmic muon-ME + … ) : ΔVTX increase as cosmic muon energy.
-> Accidental BKG : no-dependent for ΔVTX.

•KDAR neutrinos rapidly decay after the beam timing.
-> From this, we can select KDAR signals, with suppressing the Beam-neutron backgrounds.

35

Analysis Result∗ 𝜟VTX : Reconstructed vertex difference

KDAR Prompt spectrum with BKG subtraction

between prompt and delayed event of KDAR
coincidence.

• ΔVTX of data and MC are clearly agreed within the error.
• It means that a high purity of KDAR signal is obtained(BKG reduction is well done),with good MC simulation (For CCQE).

BKG ID

12

Correlated/
Accidental

BKG(# of events)

Correlated

36.6 +- 34.8 5.0 +- 5.1%

Accidental

1.5 +- 0.1

KDAR Candidates
730 events

0.2 +- 0.01%

38.1 +- 38.4 5.2 +- 5.3%
36