DIRECT MEASUREMENT OFTOPOLOGICAL INFORMATION USINGHUNI-ZICOS FOR ZR-96 NEUTRINOLESSDOBLE BETA DECAY EXPERIMENTTAUP2021 17th International Conference onTopics in Astroparticle and Underground Physics

August 31, 2021
Grant-in-Aid for Scientific Research on Innovative Areas
19H05093 and 20H05241
Scientific Research (C) 18K03664

Miyagi University of Education

Y. Fukuda, T.Shimizu, Y.Kamei,Narengeril, A. Obata, D. Anzai

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

Conceptual design of ZICOS detector
Phys.Rev.Lett. 117 (2016) 082503

0𝜈𝜈
NEMO3 : 𝑇𝑇1/2> 9.1 × 1021 yrs

96Zr : 45 kg (nat.) → 865 kg(50 % enrich)→1/20 BG

0𝜈𝜈
𝑇𝑇1/2
> 4 × 1025 yrs → 2 × 1026 yrs → ~1 ×1027yrs

Direct measurement of topological information using HUNI-ZICOS
detector for Zr-96 neutrinoless double beta decay experiment.

August 21,2022

2Discrimination of signal and BG
0νββ event
e-Reconstructed vertex byescintillation light

β decay
2.6 MeV γ
Reconstructed vertex
by Cherenkov lightBalloon orsurface ofdetector
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

e-August 21,2022

3BG reduction using topological information
Average direction=- Σ diedi θiSimulated by EGS578%
remain93%
cut

Averagedangle= Σ θi
Nhit
Topological information (averaged angle) of Cherenkov
lights could be used for reduction of 208Tl backgrounds.
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,20224

Strategy to realize 208Tl BG 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. (this autumn)
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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arbitary scale

Pulse shape of Cherenkov and scintillation• 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.
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96

August 21,2022

6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.
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96

August 21,20227

Charge ratio in rise time using ZICOS LS•••

There is difference inshape between t = 57 nsand 58 nsCharge ratio looks
depend on the energyFor 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.

Direct measurement of topological information using HUNI-ZICOS detector for Zr-96

August 21,20228

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.
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96

August 21,2022

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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

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.

Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,202210

Direct measurement of topologicalinformation using HUNI-ZICOS

2645%Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Mounting PMTs on jig for hemisphere flask

 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. August 21,2022
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96

neutrinoless double beta decay experiment.

12Setting hemisphere flask to jig and locate
on supporting stand HUNI-ZICOS was putted on flask clip and the chimney waspinched by clamp.
 Assuming e- generation position to be center of truncatedicosahedron jig (not hemisphere flask).
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,202213

Cable connection to FADC and HV
LeCroy 1182 ADC

All channels are connected
to FADC V1742 digitizer.
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Electron with fixed direction and fixedenergy using 88Y gamma source• Compton scatteringwith fixed direction
generates fixedenergy electron.
• Compton angle 100
degree corresponds
to 352 keV for
scattered γ and 1.484
MeV for electron.
• Cherenkov angle is
47 degree.
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Measurement of averaged angle using 88Y
La-GPS88Y• Scattering gammas
were detected by wellcalibrated La-GPS
scintillator through thePb collimation.

Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Event selection for scattered electron
Event selection criteria :••••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.

Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Measured averaged angle and sumulation•••

Averaged angle measured by HUNIZICOS has a peak at 40 degree. Thisis not consistent with the Cherenkov
angle. This is due to PMT geometryof HUNI-ZICOS 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.
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Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

Demonstration of 208Tl BG reduction
Al2O3(t=1.3mm)
base of Si SSD

SSD for EXT trigger

5045%

Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Demonstration of 208Tl BG reduction

SSD for EXT trigger

5045%• Data taking will start in this autumn.
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Observation of 2νββ signal using 2ν-ZICOS• 28 cm diameter flask
using Ultra-pure quartz
and 60 low ＢＧ 2” PMT
Hamamatsu R3378-50(R2083)• 18.5cm inner balloon• 300g Zr(iPrac)4 loaded
liquid scintillator whichcontains 1.1 g 96Zr
• 180 2νββ events peryear is expected• Location: Kamioka mine
• Start time: FY2024
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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Observation of 2νββ signal using 2ν-ZICOS• 28 cm diameter flask
using Ultra-pure quartz
and 60 low ＢＧ 2” PMT
Hamamatsu R3378-50(R2083)• 18.5cm inner balloon• 300g Zr(iPrac)4 loaded
liquid scintillator whichcontains 1.1 g 96Zr
• 180 2νββ events peryear is expected• Location: Kamioka mine
• Start time: FY2024
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,202222

Summary•••••

Topological information (averaged angle) of Cherenkov light
was directly measured by HUNI-ZICOS using actual low
energy electron.
Averaged angle distribution using fixed direction and fixedenergy (1.484MeV) electron using 88Y source has peak at~40 degree. This is not Cherenkov angle due to hit PMT
geometry. They also agree with the simulation.
It is verified that Cherenkov light emitted from 1.484MeV
electron really maintain their topology, in other words, 208Tl
BG reduction using averaged angle is possible even for
scintillator experiment.
Demonstration of βγ BG reduction using 60Co source by UNIZICOS will be started in this autumn and the result will bereported at early next year.
Next program to observe 2νββ decay will start in FY2024
after 2 years construction and checking. Stay tuned!
Direct measurement of topological information using HUNI-ZICOS detector for Zr-96
neutrinoless double beta decay experiment.

August 21,2022

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