DIRECT MEASUREMENT OF TOPOLOGICAL INFORMATION USING HUNI-ZICOS FOR ZR-96 NEUTRINOLESS DOBLE BETA DECAY EXPERIMENT

(1)

DIRECT MEASUREMENT OF

TOPOLOGICAL INFORMATION USING HUNI-ZICOS FOR ZR-96 NEUTRINOLESS

DOBLE BETA DECAY EXPERIMENT

TAUP2021 17 th International Conference on Topics 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. Hayami

(2)

August 21,2022 Direct measurement of topological information using HUNI-ZICOS

detector for Zr-96 neutrinoless double beta decay experiment.

2

Conceptual design of ZICOS detector

96 Zr : 45 kg (nat.) → 865 kg(50 % enrich)→1/20 BG 𝑇𝑇 1/2 0𝜈𝜈 > 4 × 10 25 yrs → 2 × 10 26 yrs → ~1 × 10 27 yrs

NEMO3 : 𝑇𝑇 1/2 0𝜈𝜈 > 9.1 × 10 21 yrs

Phys.Rev.Lett. 117 (2016) 082503

(3)

Discrimination of signal and BG

Balloon or surface of

e-

2.6 MeV γ

e-

Reconstructed vertex by e- scintillation light

Reconstructed vertex by Cherenkov light

0νββ event

β decay

(4)

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

neutrinoless double beta decay experiment.

4

BG reduction using topological information

Topological information (averaged angle) of Cherenkov lights could be used for reduction of 208 Tl backgrounds.

78% remain 93% cut

Simulated by EGS5

e - θ i

Average direction

= Σ d i d i

Averaged angle= Σ θ i

Nhit

(5)

Strategy to realize 208 Tl 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 (averaged

angle) of Cherenkov light. (this autumn)

(6)

neutrinoless double beta decay experiment

6

Pulse shape of Cherenkov and scintillation

• Pulse shape of 90 Sr 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 Q time /Q total . Here, Q time is FADC count in each time, and Q total is sum count of FADC between 55 ns and 80 ns.

ar bi ta ry scal e

(7)

Q total distribution for γ sources

• 60 Co (1.17 MeV/1.33 MeV) Compton edge ： 1.04 MeV

• 137 Cs (662 keV)

Compton edge ： 478 keV

• 133 Ba (356 keV)

Compton edge ： 207 keV

• 57 Co (122 keV which is under Cherenkov threshold

“168 kev”)

Pulse shape with charge

ratio in each FADC time.

(8)

neutrinoless double beta decay experiment

8

Charge ratio in rise time using ZICOS LS

• There is difference in

shape 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 of

scintillation between 57 ns

and 58 ns for 57 Co.

(9)

χ 2 distribution using 57 Co template

• Most of backgrounds have lower χ 2 than 1.0

• Most of backgrounds have lower energy than Cherenkov threshold, then only scintillation was seen.

It seems to events with

Cherenkov lights should

have large χ 2 value.

(10)

10

Measured by Compton edge event and BG sample

χ 2 ＜ 0.1(scintillation like)

403/3970 = 10.4 ± 0.5% for

Compton 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 - was

strongly indicated.

(11)

Direct measurement of topological information using HUNI-ZICOS

26

45%

(12)

12

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 covered

around the hemisphere flask

in this time.

(13)

Setting hemisphere flask to jig and locate on supporting stand

 HUNI-ZICOS was putted on flask clip and the chimney was pinched by clamp.

 Assuming e - generation position to be center of truncated

icosahedron jig (not hemisphere flask).

(14)

14

Cable connection to FADC and HV

All channels are connected to FADC V1742 digitizer.

LeCroy 1182 ADC

(15)

Electron with fixed direction and fixed energy using 88 Y gamma source

• Compton scattering with fixed direction generates fixed

energy electron.

• Compton angle 100 degree corresponds to 352 keV for

scattered γ and 1.484 MeV for electron.

• Cherenkov angle is

47 degree.

(16)

16

Measurement of averaged angle using 88 Y

• Scattering gammas were detected by well calibrated La-GPS

scintillator through the Pb collimation.

La-GPS

88 Y

(17)

Event selection for scattered electron

Event selection criteria :

• Number of PMT hit for BG are clustered below 5 hit.

1) Nhit ≧ 5

• Qtotal for BG are also clustered below 1000.

2) Qtotal ≧ 1000

• Observed energy of scattering gamma is clustered around 352keV.

• Due to SC-37 (UV cut) filter, we observed almost only

Cherenkov light in this time.

(18)

18

Measured averaged angle and sumulation

• Averaged angle measured by HUNI- ZICOS has a peak at 40 degree. This is not consistent with the Cherenkov angle. This is due to PMT geometry of HUNI-ZICOS detector.

• Averaged angle obtained by EGS5 simulation of Cherenkov light has a peak at 40 degree. This is consistent with above measurement.

• Averaged angle obtained by EGS5 simulation of scintillation has a peak around 50 degree. This is quite

different from Cherenkov light.

Verified Cherenkov lights emitted

from 1.484 MeV electron really

maintain their topology.

(19)

Demonstration of 208 Tl BG reduction

50

45%

SSD for EXT trigger

Al

₂

O

₃

(t=1.3mm)

base of Si SSD

(20)

20

Demonstration of 208 Tl BG reduction

• Data taking will start in this autumn.

50

45%

SSD for EXT trigger

(21)

Observation of 2 νββ signal using 2 ν -ZICOS

• 28 cm diameter flask using Ultra-pure quartz and 60 low ＢＧ 2” PMT Hamamatsu R3378-50 (R2083)

• 1kg Zr(iPrac) 4 loaded liquid scintillator which contains 4 g 96 Zr

• 800 2 νββ events per year is expected

• Location: Kamioka mine

• Start time: FY2024

(22)

22

Observation of 2 νββ signal using 2 ν -ZICOS

• 28 cm diameter flask using Ultra-pure quartz and 60 low ＢＧ 2” PMT Hamamatsu R3378-50 (R2083)

• 1kg Zr(iPrac) 4 loaded liquid scintillator which contains 4 g 96 Zr

• 800 2 νββ events per year is expected

• Location: Kamioka mine

• Start time: FY2024

Stay tuned!

(23)

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 fixed energy (1.484MeV) electron using 88 Y 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, 208 Tl BG reduction using averaged angle is possible even for scintillator experiment.

• Demonstration of βγ BG reduction using 60 Co source by UNI- ZICOS will be started in this autumn and the result will be reported at early next year.

• Next program to observe 2 νββ decay will start in FY2024

(24)

24

Backup slides

(25)

Measured hitmap and simulation

• Most distinct feature of topology for Cherenkov lights is appeared in

PMT hitmap, because of fixed direction of incident electron.

• There seems to be structures in hitmap in case of simulation as expected.

• There was also almost same

structure in selected event data as

simulation. This is clear evidence

why the topology of Cherenkov

light maintains even for 1MeV

electron.

(26)

26

e - θ i

Average direction

= Σ d i

d i Averaged angle= Σ θ i

Nhit

Topological info : averaged angle

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.

(27)

Requirement : Low BG, Large target mass, Good E-resolution

[T 1/2 0ν ] -1 =G 0ν (E 0 ,Z)|M 0ν | 2 <m ββ > 2 /m e 2

T 1/2 ~a(Mt/ ∆ E ・ B) 1/2 a: abundance M: target mass t: measuring time ∆ E: energy resolution B: BG rate

Neutrinoless double beta decay

(28)

August 21,2022 Direct measurement of topological information using HUNI-

ZICOS detector for Zr-96 neutrinoless double beta decay

experiment.

28

3.5m

10m

Liquid Scintillator ：

(1) 10 wt.% Zr(iprac) 4 loaded in Liquid Scintillator

(2) 3~4% at 3.35MeV of energy resolution with 64% photo

coverage and long attenuation length.

Inner detector with ~64% photo coverage 20” PMT including 1.7ton Zirconium loaded 113 tons LS in fiducial volume. (Total vol. : 180 tons)

Pure water surrounding inner

detector in order to veto muons and

external backgrounds. 10m

ZICOS experiment for neutrinoless double beta decay using 96 Zr

Purpose:

① Direct measurement of 0νββ

② Confirm parameter of nuclear

matrix element model

(29)

> 70g/L of Zirconium could be solved in anisole.

Liquid Scintillator solving Zr(iPrac) 4

Zr(iprac) 4 2242mg, PPO 999mg and POPOP 10mg solved in 20mL Anisole

Zr(CH 3 COCHCOOCH(CH 3 ) 2 ) 4

= Zr(iPrac) 4

mw : 663.87

(30)

30

Measured by fixed energy fixed direction events

χ 2 >0.1 ： 22events/28events

=78.6%

BG events=3evets

Fixed energy : 835keV ADC ch~3400cn

If the events with χ 2 >0.1

should have Cherenkov

lights, is this inefficiency

21.4 ± 9.6% correct?

(31)

Check V1742 sampling waveform

• Sampling frequency of V1742 was set as

5GS/s (fastest mode)

• Sampling frequency of V1751 was set as

1GS/s due to 8ch

read.(No DES mode)

• Waveform of same

Cherenkov pulse was completely same shape.

• Detailed pulse structure analysis is available

using V1742.

(32)

32

Flash ADC V1742 and PMT HV system

Both CAEN HV AG7030SN and FADC V1742 32ch

(5Gs/s!) were checked and

ready for the measurement.

(33)

Decay scheme of 208 T ｌ

The vertex position reconstructed by scintillation might be within

fiducial volume due to gammas.

(34)

34

Property of Cherenkov light

 Refractive index of anisole : n=1.518

 Cherenkov angle is determined by cos θ = 1/n β

 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