VERIFICATION OF TL-208 BACKGROUNDSREDUCTION FOR NEUTRINOLESS DOUBLEBETA DECAY WITH HALF-LIFE 10 TO 27THYEARS USING ZR-96
研究会「ニュートリノを伴わない二重ベータ崩壊とその周辺」

12th February, 2021
Grant-in-Aid for Scientific Research on Innovative Areas
19H05093 and 20H05241
Miyagi University of Education

Y. Fukuda, Narengerile, A. Obata,Y. Kamei, D. Anzai

Kamioka Observatory, ICRR, Univ. of Tokyo S. Moriyama, K. Hiraide
Fukui University I. Ogawa
Tokyo University of Science

T. Gunji, S. Tsukada, R. Hayami

Institute for Materials Research, Tohoku University S. Kurosawa

Neutrinoless double beta decay[T1/20ν]-1 =G0ν(E0,Z)|M0ν|2<mββ>2 /me2
T1/2~a(Mt/∆E・B)1/2

a: abundance

M: target masst: measuring time ∆E: energy resolution B: BG rate

Requirement : Low BG, Large target mass, Good E-resolution
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Future Neutrinoless double beta decay
experiments

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Current limits and future goal

J.Detwiler@nu2020

 To cover IH region, measure T1/2≧1027 years
 To reach NH region, need T1/2~1028 years measuring
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Techniques for Neutrinoless double beta
decay experiment

MTD

J.Detwiler@nu2020
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J.Detwiler@nu2020

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Sensitivity for some experiments

J.Detwiler@nu2020

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ZICOS experiment for neutrinoless double
beta decay using 96Zr
Liquid Scintillator：(1) 10 wt.% Zr(iprac)4 loaded in
Liquid Scintillator(2) 3~4% at 3.35MeV of energy
resolution with 64% photocoverage and long attenuation
length.

3.5m

Pure water surrounding innerdetector in order to veto muons andexternal backgrounds.
Inner detector with ~64% photo
coverage 20” PMT including 1.7ton
Zirconium loaded 113 tons LS in
fiducial volume. (Total vol. : 180tons)
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10m

10m

Purpose:① Direct measurement of 0νββ
② Confirm parameter of nuclear
matrix element modelFeb 12th, 20218

Liquid Scintillator solving Zr(iPrac)4Zr(CH3COCHCOOCH(CH3)2)4= Zr(iPrac)4mw : 663.87

Zr(iprac)4 2242mg, PPO999mg and POPOP 10mg
solved in 20mL Anisole> 70g/L of Zirconium could be solved in anisole.
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Performance of liquid scintillator
Measured at several conditions of PPO concentration

48.7±7.1% light yield tostandard cocktail wasobtained at 10wt.%
concentration.
ニュートリノを伴わない二重ベータ崩壊とその周辺13.0±2.0%√(64%/9.2%)X(3.35MeV/1.03MeV)= 2.7±0.4% at 3.35MeV
Feb 12th, 2021

10Measurement for energy resolution by 20%
photo coverage

σ/E=7.0%@982
keV&20%photocoverage
2.2%@3.35MeV&60% photocoverage
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Conceptual design of ZICOS detector
Phys.Rev.Lett. 117 (2016) 082503

0𝜈𝜈
NEMO3 : 𝑇𝑇1/2> 9.1 × 1021 yrs

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

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

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Decay scheme of 208Tｌ

The vertex position reconstructedby scintillation might be within
fiducial volume due to gammas.
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Discrimination of signal and BG0νββ event
e-Reconstructed vertex byescintillation light

β decay
2.6MeV γ
Reconstructed vertex
by Cherenkov light
Balloon or
surface ofdetector
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Topological info : averaged angle
Average directione- = Σ didi θi

Averagedangle= Σ θi
Nhit

Average angle with respect to averaged direction
for single electron seems to have a peak at 48
degree which is almost same as Cherenkov angle.
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BG reduction using topological information
Simulated by EGS5Simulated by EGS578%
remainVertex position
Double beta decay event sample
Simulated by EGS593%
cut

Topological information from
PMT position which received
PMT hit pattern of 208Tl BG and Cherenkov lights could be
used for reduction of 208Tl BG.
0νββ signal
Vertex position

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Measurement of pulse shape difference
FADC digitizer: CAEN V1751
 10 bit 2 GS/s (interleaved) – 1 GS/s ADC
 4-8 channel
 FPGA for real time Digital Pulse Processing: Pulse Shape Discrimination (DPP-PSD)
 Zero Length Encoding (DPP-ZLEplus)
 0.2 or 1 Vpp input dynamics single ended or 1 Vpp differential
 16-bit programmable DC offset adjustment: ±0.5 V / ±0.1 V
 Trigger Time stamps
 Memory buffer: up to 14.4 MS/ch (28.8 MS/ch @2 GS/s)
 Programmable event size and pre-post trigger adjustment
 Analog Sum/Majority and digital over/under threshold flags for
Global Trigger logic
 Front panel clock In/Out available for multiboard synchronisation(direct feed through or PLL based synthesis)
 16 programmable LVDS I/Os
 Optical Link interface (CAEN proprietary protocol)
 VME64X compliant interface A2818(PCI) / A3818 (PCIe) Controller available for handling up to8/32 modules Daisy chained via Optical Lin Firmware upgradeable via VME/Optical Link
 Libraries, Demos (C and LabView) and Software tools for Windows andLinuxFeb 12th, 2021
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Measurement of pulse shape difference
Photomultiplier : Hamamatsu H2431-50 (R2083)

 Spectral response ：４００K QE: 25% at peak Dynode structure : linear focused/8 dinodes
 High voltage ：３０００V
 Gain：2.5×106 dark current :100nA (H6410:10nA)
 Time response ：0.37ns(TTS) 0.7ns（rise time）
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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 :4.57ns and 8.38ns• Rise time of scintillation :1.45ns• Rise time of Cherenkov :0.75nsUse the charge ratio Qtime/Qtotal. Here, Qtimeis FADC
value in each time, and Qtotalis sum of FADC value
between 55ns and 80ns.
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Qtotal distribution for γ sources••••

60Co (1.17MeV/1.33MeV)

Compton edge： 1.04MeV
137Cs (662keV)
Compton edge： 478keV
133Ba (356keV)
Compton edge： 207keV
57Co (122keV)
Under Cherenkov threshold(169kev)

Pulse shape with charge
ratio in each FADC time.
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Charge ratio in rise time using ZICOS LS•••

There is difference ofshape between t=57nsand 58ns
Charge ratio looks
depend on the energy
For t>58.5ns, all shapes
were almost same.
Cherenkov looks dominant
between 57ns and 58ns.
Template waveform ofscintillation between 57.0ns
and 58.0ns for 57Co.

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21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.
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Measured by fixed energy fixed direction events

χ2>0.1：22events/28events=78.6%

BG events=3evets
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Fixed energy : 835keV
ADC ch~3400cn
If the events with χ2>0.1
should have Cherenkov
lights, is this inefficiency
21.4±9.6% correct?
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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

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1772/3606=49.1±1.4% for
BG sample
Inefficiency value between
Compton edge and BG
sample differs with 2.86σ.
Topology of Cherenkov
lights for O(1)MeV ewas confirmed.
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Measurement of topological information(averaged angle) using HUNI-ZICOS

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3/8” photomultiplier H3164-12(R1635)

 Sensitivity：４００K
 Dynode type : Line focus/8dynode Applied voltage：125０V
 Gain：1.0×106 Dark current: 50nA
 Time characteristics：0.5ns(TTS) 0.8ns（rise time）
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Pulse shape measurement by H3164-12

Cherenkov dominant
Scintillation dominant
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Pulse Shape Discrimination using H3164-12

It’s possible but need tuning.
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Hemisphere flask and PMT fixing jig for HUNIZICOS

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Extension sharpening for hemisphere flaskand PMT

 Extension sharpening for hemisphere flask was almost done.
 Some extensions for PMT hole should be necessary.
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Flash ADC V1742 and PMT HV system

Both CAEN HV AG7030SN
and FADC V1742 32ch
(5Gs/s!) were checked andready for the measurement.
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Summary••

High Zr concentrated liquid scintillator is available.
Expected energy resolution 2.2％＠3.35ＭｅV&20% photocoverage→ need to confirm with real 60% photo coverage• To establish background reduction technique for 208Tl decay→ topological information using Cherenkov lights is useful.
① Pulse shape discrimination for selection of PMT which
receives Cherenkov lights : almost done
② Confirmation of topological information : HUNI-ZICOS will
be ready to measure soon.
③ Verification of βγ events reduction using topologicalinformation : UNI-ZICOS will start in next fiscal year.

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Verification of 208Tl BG reduction• Direct measurement using βγ events by UNI-ZICOS

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Summary••

High Zr concentrated liquid scintillator is available.
Expected energy resolution 2.2％＠3.35ＭｅV&20% photocoverage→ need to confirm with real 60% photo coverage• To establish background reduction technique for 208Tl decay→ topological information using Cherenkov lights is useful.
① Pulse shape discrimination for selection of PMT whichreceives Cherenkov lights : almost done
② Confirmation of topological information : HUNI-ZICOS will
be ready to measure soon.
③ Verification of βγ events reduction using topologicalinformation : UNI-ZICOS will start in next fiscal year.
• Physics program (measurement of 96Zr 2νββ T1/2) withZICOS-I will start soon and get results within 5 years.

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Measurement of T2ν1/2 for 96Zr using ZICOS-I• First physics program to measure T2ν1/2 for 96Zr

・20cm diameter flask
using Ultra-pure quartz
and 30 low ＢＧ 2” PMTR3378-50 (R2083)
・Synthesis Zr(iPrac)4300g which corresponds
to 96Zr isotope1g
・According to NEMO-3result, expect 200 2νββevents/year
・Location: Kamioka mine
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Stay tuned!

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Summary••

High Zr concentrated liquid scintillator is available.
Expected energy resolution 2.2％＠3.35ＭｅV&20% photocoverage→ need to confirm with real 60% photo coverage• To establish background reduction technique for 208Tl decay→ topological information using Cherenkov lights is useful.
① Pulse shape discrimination for selection of PMT which
receives Cherenkov lights : almost done
② Confirmation of topological information : HUNI-ZICOS will
be ready to measure soon.
③ Verification of βγ events reduction using topologicalinformation : UNI-ZICOS will start in next fiscal year.
• Physics program (measurement of 96Zr 2νββ T1/2) withZICOS-I will start soon and get results within 5 years.
• Future program for 0νββ search will start after ZICOS-I with
100g~1kg of 96Zr using ZICOS-II detector. (need enrichment)
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Backup slides

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Property of Cherenkov light Refractive index of anisole : n=1.518
 Cherenkov angle is determined bycosθ= 1/nβ Assuming 1.65MeV electron, then
β=0.972 and Cherenkov angel θ=47.3
degree are expected.
 Cherenkov light should be measured.
(400nm – 600nm : 100 photon/MeV )c.f. Light yield of Scintillation : ~12000photon/MeV

Cherenkov light = 1~2% of scintillation light
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Emission and absorption spectra forsolvent and solute in standard cocktailPPO absorbed mostof emission lights fromanisole.
Effectively the energy
was transferred to thesecondary scintillator.
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Absorbance spectra for Zr(iprac)4
Absorption peaks ofZr(iprac)4 was foundaround at 278nm.
However, overlapped
region with emissionof anisole was existed.
Zr(iprac)4 works as aquencher for the liquid
scintillator system.
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