Present status of experiment for Zirconum-96 two neutrino emission
double beta decay
The XXXI International Conference on Neutrino Physics and Astrophysics (NEUTRINO 2024)
June 16 – 22 2024 Milan, Italy
Y.Fukudaa, K.Hiraideb, S.Moriyamab, I.Ogawac, T.Gunjid, S.Kurosawae and Y.Nakanofa Miyagi Univ. of Education, b Kamioka Observatory, ICRR, Univ. of Tokyo, c Univ. of Fukui, dTokyo Univ. of Science, eIMR Tohoku Univ., f Univ. of Toyama

Supported by Grant-in-Aid for Scientific Research on Innovative Areas 20H05241,19H05093 and Scientific Research (B) 22H01243, 23K22514

1.

96
ZICOS ( Zr DBD experiment)◆ Neutrinoless Double Beta Decay● Lifetime and neutrino mass

[T1/20ν(0+ ->0+)]-1 =G0ν(E0,Z)|M0ν|2<mν>2● Energy spectrum and lifetime measurement・monochromatic energy at Q-value
・T1/2~a(Mt/∆EB) a: abundance M: masst: meas.time ∆E: energy res. B: BG rate

Low background rate, Large target mass and High energy resolution◆ Detector Design for ZICOS Experiment98
4. Zr two neutrino emission DBD◆ 2ν-ZICOS Detector• 16 cm diameter round bottom flask using UltraPure Quartz (GE214) [Th 15ng/g, U 29ng/g]• 20 low ＢＧ 2” PMT Hamamatsu H3378-50• Al regular icosahedron PMT mounting jig• ZICOS liquid scintillator [Th < 50ng/g, U < 50ng/g]
1L loaded 100g Zr(iPrac)4 corresponds 0.4 96Zr.
• Expected number of 2νββ events : ~100 per year.
• Experimental site : LAB-A in Kamioka mine

entrance

Detector :1)180tons LS : 10 wt.% tetrakis(isopropyl acetoacetato)zirconium: Zr(iPrac)4 5 wt.% PPO in Anisole.
2) Fast rise time and TTS PMT with
64% photo coverage.

Expected performance :1)Energy resolution ~2.8%@3.35MeV
2)T1/2(0νββ) > 1027years if both 1/20
BG reduction using Topology ofCherenkov light and 50% 96Zr
enrichment could be achieved.

5. Present status of 2ν-ZICOS exp.
◆ Preparation of 2Little ZICOS Liquid Scintillator

208
2. How to reduce Tl BG events◆ Conceptional Idea using Cherenkov Lights
0νββ evente-

Reconstructed vertex
by scintillation light e-1β decay
2.6MeV γ
Event generatedpositione-Surface ofdetector wall
208Tl β decay event

Vertex position obtainedby scintillation
Averageddirection = Σ diAveraged
angle= Σ θi
Nhit

Averaged angle has topology ofCherenkov light and could be used fortool of 208Tl BG event reduction.

e-◆ ETFE Cubic Bag for ZICOS LSdi θi◆ Direct Observation of Averaged Angle for Cherenkov Lights

using 88Y FDFE Events

・ Averaged angle
was clusteredaround 45 deg forelectrons with
fixed direction
and fixed energy.
・ Simulation
indicates also apeak around 48
deg. as expected.
Averaged angle isreally observed.

◆ PSD using V1742 and H3378-50

Photomultiplier

3. Demonstration of BG reduction◆ Observed Averaged Angle

No difference between liquid scintillator with old Zr(iPrac)4 synthesized
by Prof. Gunji and new Zr(iPrac)4 synthesized by NARD Institute.

◆ Expected Averaged Angle
using 60Co Beta-Gamma

・ Vertex position
was reconstructedby assuming all
PMTs have same
effective charge.
・ Averaged angleof 60Co βγ events
has a peak around60 deg.
Averaged angle
could reduce
208Tl BG events.

The transparency of 100µm ETFE : 0.9566±0.0027◆ Design of Radiation Shield
Radiation
shieldconsists of450 Pb
blocks, 3mmt
OFC plates,
50 paraffinblocks andPSD to select PMT received
Al frame +Cherenkov light has beenplate on Fe
established using waveformbasis.
of V1742 and H3378 PMT.

6. Future plan

• Detector performances such as the energy resolution, the vertex
reconstruction, and the averaged angle will be measured soon.
• Accepted for ICRR Inter-University Research Program.
• Need permission from Kamioka Steering Committee.
• Construction schedule after the permission.
a. Install clean booth and setup the radiation shield in the cleanbooth at LAB-A. (~1 month)b. Install 2ν-ZICOS detector inside of Radiation shield. (~2 months)• Data taking hopefully will start in 2025