ジルコニウム96を用いたニュートリノを放出しない
二重ベータ崩壊事象の探索XIX～ベータ線とガンマ線によるチェレンコフ光の位相幾何学情報の測定～
日本物理学会2022年秋季大会

September 7, 2022

Grant-in-Aid for Scientific Research on Innovative Areas
19H05093 and 20H05241
Scientific Research (B) 22H01243
Miyagi University of Education

Y. Fukuda, T. Shimizu*

Kamioka Observatory, ICRR, Univ. of Tokyo S. Moriyama, K. Hiraide
University of Fukui I. Ogawa
Tokyo University of Science T. Gunji, S. Tsukada, R. Hayami
Institute for Materials Research, Tohoku University S. Kurosawa

Conceptual design of ZICOS detector
Phys.Rev.Lett. 117 (2016) 0825030𝜈𝜈NEMO3 : 𝑇𝑇1/2> 9.1 × 1021 yrs

96Zr : 45 kg (nat.) → 865 kg(50 % enrich)→1/20 BG0𝜈𝜈𝑇𝑇1/2> 4 × 1025 yrs → 2 × 1026 yrs → ~1 ×1027yrs

日本物理学会 2022年秋季大会

Sep 7,2022

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Discrimination of signal and BG
0νββ evente-

Reconstructed vertex byescintillation light

β decay
2.6 MeV γ
Reconstructed vertex
by Cherenkov light
Balloon or
surface ofdetector
日本物理学会 2022年秋季大会

e-Sep 7,2022

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Verification of 208Tl background reduction
using Cherenkov lights
1. Selection of PMTs which receive Cherenkov
lights among huge Scintillation lights.
• Pulse shape discrimination
2. Confirm topology of Cherenkov lights• Directionality of Cherenkov lights• Direct measurement of topological information
averaged angle
3. Demonstrate BG reduction using beta-gamma
sources with topological information (averagedangle) of Cherenkov light.
日本物理学会 2022年秋季大会

Sep 7,2022

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Pulse shape of Cherenkov and scintillation
arbitary scale• Pulse shape of 90Sr using
H2431-50 measured by
V1751 with DES mode
(2GS/s)• Decay time of scintillation :4.57 ns and 8.38 ns• Rise time of scintillation :1.45 ns• Rise time of Cherenkov :0.75 ns
Use the charge ratio Qtime/Qtotal. Here, Qtimeis FADC
count in each time, and Qtotalis sum count of FADC
between 55 ns and 80 ns.
日本物理学会 2022年秋季大会

Sep 7,2022

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Demonstration of 208Tl BG reduction using
UNI-ZICOS detector

Due to the earthquake in March, we lost 5 PMTs.

日本物理学会 2022年秋季大会

Sep 7,2022

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Topological information of Cherenkov lights
Average direction =Σ- di (di : unit vector)
eVertexpositiondi θiAveragedangle= Σ θiNhit
Topological information (averaged angle) of Cherenkov
lights should be different between β and β + γ event.
日本物理学会 2022年秋季大会

Sep 7,20227

Setup for measurement with UNI-ZICOS

Source holder has
a hole, and it canbe covered by Alplate (0.3mm and2mm) to terminate
betas.
The vertex position could be reconstructed by assuming that all PMTs should havesame effective charge which is corrected by the distance between PMT and vertex.
日本物理学会 2022年秋季大会

Sep 7,2022

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Observed averaged angle using FDFE events•••••
日本物理学会 2022年秋季大会

The vertex position was reconstructedby charge information as explained.
Extracted PMTs which include
Cherenkov light by PSD technique.
Using those PMTs and the vertex, theaveraged angle of fixed direction fixedenergy (1.484MeV) electron from 88Y
source was measured, and a peak
was found around 50 degree.
The averaged angle obtained by MC
simulation has a peak around 48degree. Within the statistical error, thepeak position was almost reproduced.
Measurement time was limited byMarch earthquake in Japan.
Sep 7,2022

9Events selection for β+γ rich samples(Al 2mm)(Al 2mm)γ events(E<1.48MeV)(Al 2mm)γ events

γ events(E<1.48MeV)

γ events

日本物理学会 2022年秋季大会(Al 2mm)(E<1.48MeV)

Sep 7,2022

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Observed averaged angle using β−γ events• Clear averaged angle of β +γ events is obtained bysubtraction of those data.
• Obtained averaged angle
has a peak around 58 deg.
• Averaged angles ofMC(β(E<0.3MeV) + γ)
reproduce peak, but not
reproduce shape.
• Averaged angle ofMC(β(E<1.48MeV) + γ) may
help to reproduce larger
angle shape.
日本物理学会 2022年秋季大会

Sep 7,2022

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Observed averaged angle using β−γ events• Clear averaged angle of β +γ events is obtained bysubtraction of those data.
• Obtained averaged angle
has a peak around 58 deg.
• Averaged angles ofMC(β(E<0.3MeV) + γ)
reproduce peak, but not
reproduce shape.
• Averaged angle ofMC(β(E<1.48MeV) + γ) may
help to reproduce larger
angle shape.
日本物理学会 2022年秋季大会

Sep 7,2022

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Observed averaged angle using β−γ events•••••

日本物理学会 2022年秋季大会

0.3mm Al plate terminates β(E<0.3MeV) events.
Small difference between 2mm Al
on and off
Obtained averaged angle has
small peak around 60 deg.
A peak of averaged angle inprevious page is caused by mainly
β (E<0.3MeV).
MC(β(E<1.48MeV) + γ ) looks
reproduce small peak without
lower angle shape too.

Sep 7,202213

Observed averaged angle using β−γ events•••••

0.3mm Al plate terminates β(E<0.3MeV) events.
Small difference between 2mm Al
on and off
Obtained averaged angle hassmall peak around 60 deg.
A peak of averaged angle inprevious page is caused by mainly
β (E<0.3MeV).
MC(β(E<1.48MeV) + γ ) looks
reproduce small peak without
lower angle shape too.

Averaged angle could be usedfor reduction of β + γ events
such as 208Tl decay background.
日本物理学会 2022年秋季大会

Sep 7,2022

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Observation of 2νββ signal using 2ν-ZICOS• 20 cm diameter flask
using Ultra-pure quartz
and 31 low ＢＧ 2” PMT
Hamamatsu R3378-50(R2083)• Filled 3L of ZICOS-LS• Loaded 300g Zr(iPrac)4
which contains 1.1 g
96Zr• 200 2νββ events peryear is expected• Location: Kamioka mine
• Start time: FY2024
日本物理学会 2022年秋季大会

Sep 7,2022

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Observation of 2νββ signal using 2ν-ZICOS• 20 cm diameter flask
using Ultra-pure quartz
and 31 low ＢＧ 2” PMT
Hamamatsu R3378-50(R2083)• Filled 3L of ZICOS-LS• Loaded 300g Zr(iPrac)4
which contains 1.1 g
96Zr• 200 2νββ events peryear is expected• Location: Kamioka mine
• Start time: FY2024
日本物理学会 2022年秋季大会

Sep 7,2022

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Summary••••

Topological information (averaged angle) of Cherenkov
light was directly measured by UNI-ZICOS using fixed
direction / fixed energy (1.484MeV) electron from 88Y
source, and the averaged angle has a peak around 48
degree as expected by MC simulation. This isconsistent with the Cherenkov angle.
The averaged angle of β (E<0.3MeV) + γ events from60Co source was measured by UNI-ZICOS, and theaveraged angle has a peak around 58 degree as
expected by MC simulation.
We succeeded to demonstrate β + γ event reduction
such as 208Tl BG using the averaged angle!
Next program to observe 2νββ decay of 96Zr will start in
FY2024 after the screening of low BG materials, thesynthesis of Zr(iPrac)4, and the construction of low BG
environment using Pb shield. Stay tuned!

日本物理学会 2022年秋季大会

Sep 7,202217

backup

日本物理学会 2022年秋季大会

Sep 7,2022

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Observed averaged angle using β−γ events•••

preliminary•

Averaged angle is obtainedby z>0 and by subtracting γ+βand γ dominant data.
Obtained averaged angle hastwo peaks around 50 and 60deg.
Events consists not only γ+β
events but β and γ onlyevents.
Averaged angles of MC forγ+β and β and γ only events
may reproduce those data.

It would be possible to reduce β+γ evens suchas 208Tl backgrounds using the averaged angle!
Reduction of Tl-208 background for Zr-96 Neutrinoless Double Beta Decay experiment using
topological information of Cherenkov lights

July 8,2022

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Measured by Compton edge event and BG sample

χ2 ＜0.1(scintillation like)
403/3970 = 10.4±0.5% forCompton edge event

日本物理学会 2022年秋季大会

1772/3606=49.1±1.4 %for BG sample
The difference between
Compton edge events and
BG sample is 2.9 σ.
Topology of Cherenkov
lights for ~1 MeV e- wasstrongly indicated.
Sep 7,202220

Qtotal distribution for γ sources••••

60Co (1.17 MeV/1.33 MeV)

Compton edge： 1.04 MeV
137Cs (662 keV)
Compton edge： 478 keV
133Ba (356 keV)
Compton edge： 207 keV
57Co (122 keV which is under
Cherenkov threshold“168 kev”)

Pulse shape with charge
ratio in each FADC time.
日本物理学会 2022年秋季大会

Sep 7,202221

χ2distribution using 57Co template• Most of backgrounds
have lower χ2 than 1.0• Most of backgrounds
have lower energy than
Cherenkov threshold,then only scintillation
was seen.

It seems to events with
Cherenkov lights shouldhave large χ2 value.
日本物理学会 2022年秋季大会

Sep 7,2022

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Charge ratio in rise time using ZICOS LS•••

There is difference inshape between t = 57 ns
and 58 ns
Charge ratio looks
depend on the energy
For t > 58.5 ns, all shapes
were almost same.
Cherenkov looks dominant
between 57 ns and 58 ns.
Template waveform ofscintillation between 57 nsand 58 ns for 57Co.

日本物理学会 2022年秋季大会

Sep 7,2022

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Direct measurement of topologicalinformation using HUNI-ZICOS

26
45%

日本物理学会 2022年秋季大会

Sep 7,202224

Electron with fixed direction and fixedenergy using 88Y gamma source
Average direction=- Σ diedi θiTopological information of Cherenkov lights
could be presented as averaged angle.
日本物理学会 2022年秋季大会

Averagedangle= Σ θiNhit
Sep 7,2022

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Mounting PMTs on jig for hemisphere flask

日本物理学会 2022年秋季大会

 Total 26 H3164-12 PMTs
were used for HUNI-ZICOS.
 In order to remove
scintillation light (~300nm),
SC-37 filter was coveredaround the hemisphere flask
in this time.
Sep 7,2022
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Setting hemisphere flask to jig and locate
on supporting stand HUNI-ZICOS was putted on flask
clip and the chimney was pinchedby clamp.
 Assuming e- generated position to be center of the truncatedicosahedron jig (not hemisphere flask).

日本物理学会 2022年秋季大会

Sep 7,202227

Cable connection to FADC and HV
LeCroy 1182 ADC

All channels are connected
to FADC V1742 digitizer.
日本物理学会 2022年秋季大会

Sep 7,2022

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Measurement of averaged angle using 88Y
La-GPS88Y

日本物理学会 2022年秋季大会• Scattering gammas
were detected by wellcalibrated La-GPS
scintillator through thePb collimation.
Sep 7,202229

Event selection for scattered electron
Event selection criteria :••••日本物理学会 2022年秋季大会

Number of PMT hit for BG areclustered below 5 hit.
1) Nhit ≧ 5
Qtotal for BG are also
clustered below 1000.
2) Qtotal ≧1000
Observed energy of scattering
gamma is clustered around352keV.
Due to SC-37 (UV cut) filter,
we observed almost only
Cherenkov light in this time.
Sep 7,2022

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Measured averaged angle and sumulation•••

Averaged angle measured by HUNIZICOS has a peak at 40 degree. Thisis due to PMT geometry of HUNIZICOS detector.
Averaged angle obtained by EGS5
simulation of Cherenkov light has apeak at 40 degree. This is consistent
with above measurement.
Averaged angle obtained by EGS5
simulation of scintillation has a peakaround 50 degree. This is quite
different from Cherenkov light.

Verified Cherenkov lights emitted
from 1.484 MeV electron reallymaintain their topology.
日本物理学会 2022年秋季大会

Sep 7,202231