ZICOS - Neutrinoless Double Beta Decay experimentusing Zr-96 with an organic liquid scintillator The European Physical Society Conference on High Energy Physics (EPS-HEP 2019)10 – 17 July 2019 Ghent, Belgium
Y.Fukudaa , D.Anzaia, Y.Kameia,e, K.Hiraideb, S.Moriyamab, Narengerilea, A.Obataa, I.Ogawac, T.Gunjid, S.Tsukadad , R.Hayamid, S.Kurosawafa Miyagi Univ. of Education b Kamioka Observatory, ICRR, Univ. of Tokyo c Univ. of Fukui dTokyo Univ. of Science eRCCN Tohoku Univ. fIMR Tohoku Univ.

Supported by Grant-in-Aid for Scientific Research on Innovative Areas 19H05093 and Scientific Research (C) 18K03664

1.

96
ZICOS ( Zr DBD experiment)

3. Development of reduction technique◆ Reduction of 208Tl events using Topological information fromCherenkov Lights◆ Neutrinoless double beta decay

Vertex position obtainedby scintillation● 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 rateAveraged
direction = Σ diedi θi

Simulated by EGS5

The averaged angle
distribution for single
electron has a peakat ~48 degree, whichis almost same value
as Cherenkov angle
in Anisole.

Averagedangle= Σ θiNhit

Low background rate, Large target mass and High energy resolution
Simulated by EGS5

◆ Detector design for ZICOS experiment
Simulated by EGS5

Vertex position
Double beta decay events sample

93%
cut

Vertex position

Detector :1)180tons LS : 1.5 wt.% Zr and5wt.% PPO in Anisole .
2)Need 500 of 20” PMT with highQE ~0.4 and TTS ~300ps@1pe for
64% photo coverage.

Expected performance :1)Energy resolution ~2.8%@3.35MeV
2)T1/2(0νββ) > 1027years if both 1/20
BG reduction and 50% 96Zr
enrichment could be achieved.
3)Start experiment ~2027.

78%
remainPossible to reduce
208Tl BG to be order of
1/20, if we can extract
Cherenkov lights fromscintillation.

4. How to extract Cherenkov lights◆ Pulse shape discrimination using fast FADC and fast PMTCAEN V1751
digitizer
Specification• 4channel• 10bit ADC• 2GS/s sampling• Auto/Externaltrigger◆ Neutrino mass sensitivity for ZICOS experiment・Total mass : 180ton (fiducial volume : 113ton)
・Measurement time: 2years
・10wt.% of Zr(iPrac)4 = 12.6ton of Zr(iPrac)4 includes 1.7ton of
Zirconium = 45 kg of 96Zr (using natural abundance 2.6%)
T1/20ν > 4×1025y ← Not enough for 0νββ search

The averaged angle of208Tl decay is smaller
than that of DBD.

Hamamatsu H243150
Specification• Line focus 8 steps• HV : 3000V• Gain :2.5×106• TTS : 0.37ns• Rise time : 0.7ns◆ Cherenkov lights observed by cosmic muons (Anisole with UV cut filter) Requirements in order to realize 0νββ GEN-III experiment1) 50% enrichment of 96Zr (e.g. 57.3% for NEMO-3)
then 96Zr will be 865kg
T1/20ν > 2 ×1026y
2) 208Tl background reduction
BG level < 1/20 ×KL-Zen
T1/20ν > 1 ×1027y◆ Development of Zr loeaded Liquid Scintillator(subtracted)

Fall time of Cherenkov lights is quite
different from that of scintillation
lights. (cf. PMTs were not H2431-50)◆ Cherenkov lights observed by electrons from 90Sr/90Y source using
tetrakis (isopropylacetoacetate)
Zirconium : Zr(iPrac)4
MW : 663.87

PMT H2431-50

Zr-LS: Zr(iPrac)410wt.%, PPO 5 wt.%
and POPOP 0.2wt%
solved in Anisole.
Shorter wavelength ofabsorption for Zr(iPrac)4
and amount of PPO
recover both light yieldand energy resolutionof Zr-LS .

1) Light yield : 48.7 ±7.1% of BC5052) energy resolution :13.0±2.0%√(64%/9.2%)X(3.35MeV/1.03MeV)= 2.7±0.4% at 3.35MeV (6.4% FWHM)
Need to measure real energy resolution

2. How to reduce backgrounds◆ Conceptional idea using Cherenkov lights

Reconstructed vertex
by scintillation light e-β decay
2.6MeV γ
Event generated
Surface of position
Balloon
208Tl decay event

Pulse shape discrimination will
make the identification of PMT
which receives Cherenkov lights
real using 2GS/s sampling. (Thiswill be checked within this year)

5. Present status and Future plan0νββ event
e-

There is clear difference for bothrise and fall time between
Cherenkov and Scintillation lighteven though 1GS/s sampling.

e~1/20 BG reduction could beachieved by using a topology
information of Cherenkov light.

Cherenkov light could be used for tool of 208Tl BG reduction.

 Conceptual design of ZICOS detector with 10 wt.% Zr(iPrac)4 loaded Liquid
Scintillator has 2.7% @3.35MeV energy resolution assuming 64% photo
coverage of 20” Photo-multiplier.
 A technique further 1/20 reduction of 208Tl backgrounds using PMT hit patternof Cherenkov lights was developed.
 Direct measurement of pulse shape of
Cherenkov and Scintillation light using
electrons from 90Sr/90Y beta source wasdone, and both rise and fall time werequite different from each others.
 Pulse shape discrimination could be
used for the identification of PMT
which receives Cherenkov lights.
 Averaged angle distribution will bemeasured by the dedicated detector
HUNI-ZOCOS in the next year.