ZICOS NE W PROJE CT F OR NE UT RINOL E SS DOUBL E BE T - - PowerPoint PPT Presentation

ZICOS – NE W PROJE CT F OR NE UT RINOL E SS DOUBL E BE T A DE CAY E XPE RI ME NT USING ZIRCONI UM COMPL E X IN ORGANI C L IQUI D SCINT I L L AT OR –

Re ve aling the history of the unive rse with unde rground partic le and nuc le ar re se arc h 2016

Koshiba Hall, T

• kyo

11 May, 2016 Miyagi Unive r sity of E duc ation

• Y. F

ukuda, Nar e nge r ile , A.Obata Kamioka Obse r vator y, ICRR, Univ. of T

• kyo S. Mor

iyama F ukui Unive r sity I. Ogawa T

• kyo Unive r

sity of Sc ie nc e T . Gunji, S. T sukada, R. Hayami Supported by Grant-in-Aid for Scientific Research on Innovative Areas No.24104501 and No.26105502

Requirement : Low BG, Large target mass, High energy resolution

[T

1/ 2 0ν(0+ ->0+)]-1 = G 0ν(E 0,Z)|M0ν| 2<mν>2 / me 2

T

1/ 2~a (Mt/ ∆E・B)1/ 2

a : a b unda nc e M: ta rg e t ma ss t: me a suring time ∆E : e ne rg y re so lutio n B: BG ra te

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Ma y 11, 2016

Ne utrino le ss do ub le b e ta de c a y

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~tons of target and ~zero BG detector will be necessary for next generation 0νββ experiment.

F uture 0νββ e xpe rime nts

1027~28 y

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Ba c kg ro unds a ro und 3.35Me V

I.Shimizu@Neutrino2014

0νββ signal region for 96Zr Measured by KamLAND-Zen

208Tl

In balloon

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3.0m 10m

Goals for development of LS ： (1) Zr should be solved highly in

• rder to make detector small.

(2) 3.5% at 3.35MeV of energy resolution, if ZICOS has PMTs with 40% photo coverage and long attenuation length (~10m)

Inner detector with 40% photo coverage 10” PMT including Zirconium loaded 113 tons LS Pure water surrounding inner detector in order to veto muons and external backgrounds.

10.0m

ZI COS- Zirc o nium Co mple x in Org a nic L iq uid Sc intilla to r fo r ne utrino le ss do ub le b e ta de c a y

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Ne utrino ma ss se nsitivity o f ZI COS e xpe rime nt

Results from NEMO-3 (96Zr) : T1/2

0ν > 9.2 ×1021y

<mν> 7.2 – 10.8 eV (gA=1.25,gpp=1.11,QRPA) Assuming same energy resolution, BG rate and measurement time as KamLAND-Zen (T1/2

0ν > 2.6 ×1025y )

Mass : 113 ton 10wt.% Zr(iprac)4 = 12.６ton includes 1.7ton of Zirconium = 45 kg of 96Zr (natural abundance 2.6%) ( 64kg of 136Xe = 0.2 ×KL-Zen)

(Ref: M.B.Kauer Doctor thesis for UCL(2010)) (Ref: I.Shimizu arXiv:1409.0077 (2014))

T1/2

0ν > 1.2 ×1025y ← Not enough for 0νββ search

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1) Zr enrichment 58.5% enrichment of 96Zr (e.g. 57.3% for NEMO-3) then 96Zr will be 1 ton (4.4 times 136Xe 320kg) T1/2

0ν > 5 ×1025y ; <mν> < 0.09 – 0.15 eV (QRPA)

2) Lowering BG (208Tl /214Bi) i.e. < 1/20 ×KL-Zen (~1.0events/ton/year) T1/2

0ν > 5 ×1025y

Ne utrino ma ss se nsitivity o f ZI COS e xpe rime nt

Electromagnetic isotope separation is expensive… Maybe we can……

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Zr(CH3COCHCOOCH(CH3)2)4 : Zr(iprac)4 tetrakis (isopropyl acetoacetate) zirconium mw : 663.87

Solid crystal or powder

De ve lo pme nt o f Zr lo a de d L S

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

So lub ility o f Zr(ipra c )4 fo r a niso le

Solubility > 31.2 wt.%

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

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Absorption peaks of Zr(iprac)4 was found around at 278nm. However, overlapped region with emission

• f anisole was existed.

Ab so rb a nc e spe c tra fo r Zr(ipra c )4

Zr(iprac)4 works as a quencher for the liquid scintillator system.

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Light yield = L0 × σ1Nppo σ1Nppo + σ2NZr L0 : Light yield of anisole Nppo : Number of PPO molecular in mole NZr : Number Zr complex molecular in mole σ1 : absorbance of PPO (mol-1) σ2 : absorbance of Zr complex (mol-1)

L ig ht yie ld q ue nc hing b y Zr(ipra c )4

PPO would help the recovering light yield.

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Re c o ve ring the lig ht yie ld

Measured at several conditions of PPO concentration 5wt.% PPO helps actually recovering the scintillation light yield. 48.7±7.1% light yield to standard cocktail was obtained at 10wt.% concentration.

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Re c o ve ring the e ne rg y re so lutio n

Measured at several conditions of PPO concentration 5wt.% PPO helps again the energy resolution 35% → 13%. at 10wt.%

• f Zr(iprac)4.

13.0±2.0%

√(40%/9.2%)X(3.35MeV/1.03MeV)

= 3.5±0.5% at 3.35MeV Achieved goal !

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Sta b ility o f liq uid sc intilla to r

• Feb. 27,2015
• Mar. 14, 2016

Keep transparent liquid and no precipitate is found.

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Me a sure me nt o f b a c kg ro unds fro m L S

Using subtracted # of events around 2.6MeV and 2.2MeV

214Bi < 4.9x10-20g/g 208Tl < 2.7x10-22 g/g

(238U < 6.4x10-6 g/g) (232Th < 7.4x10-7 g/g) (c.f. KL 10-18g/g)

2.615MeV (208Tl) 2.204MeV (214Bi) 1.765MeV (214Bi) 1.120MeV (214Bi) 0.609MeV (214Bi)+ 0.583MeV (208Tl)

Measured by lowBG CsI

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Ma in b a c kg ro unds fo r ZI COS

Main backgrounds evaluated by KamLAND-Zen are mainly 208Tl inside the balloon film. Need additional technique except energy spectral shape obtained by scintillation light in order to reduce those backgrounds drastically. Can we use Cherenkov lights for background reduction ?

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Pro pe rty o f Che re nko v lig ht

 Refractive index of anisole : n=1.518  Cherenkov angle is determined by cosθ= 1/n’β (Ee>0.7MeV) n’>n  Assuming 1.65MeV electron, then β=0.972 and Cherenkov angel θ=47.3 degree are expected.  Number of Cherenkov photon : 100 photon/MeV (400nm – 600nm)

c.f. Light yield of Scintillation : ~12000photon/MeV

Cherenkov light = ~1% of scintillation light

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Cherenkov light yield (λ>400nm) Scintillation light yield of std. LS 159/0.15/0.95 255/0.046/0.098

Me a sure me nt o f L Y fo r Che re nko v lig hts

400nm 500nm 600nm 90% 50% SC-37 filter

= = ~0.02

Consistent with expectation.

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Sig nific a nt b a c kg ro unds

• No Cherenkov lights (scintillation only)
• α-particle and low energy e/γ
• Observed Cherenkov lights
• Can we check the consistency of vertex position
• btained by scintillation and Cherenkov? (if we can

reconstruct vertex position using Cherenkov lights.)

208Tl : β and 2.6MeV γs 214Bi :β and multi γs (609keV,1.12MeV)

164µs

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208T

l b a c kg ro unds

Balloon film e- 2.6MeV γ e- e- Real position Reconstructed vertex by scintillation only Reconstructed vertex by Cherenkov 0νββ event

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E le c tro n kine tic e ne rg y spe c trum

For calculation of 2νββ, ki, electron momenta εi =sqrt(ki

2+me 2) : electron energy

W0=Q+2me : total release energy Q : Q value me: electron mass θ : opening angle F : Fermi func. εi can generate independently within energy conservation. For calculation of 0νββ, Same calculation but εi can only generate with ε1+ε2=W0.

2e emit Cherenkov lights

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Multiple sc a tte ring o f e le c tro ns

In fact, electrons should be scattered by multiple scattering, however Cherenkov light looks have some clusters in direction.

Event direction

Simulated by EGS5

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Me a sure me nt o f Che re nko v lig ht

Comparison of light yields with several angle with respect to direction of incident gamma.

50 deg

47deg 60Co

NaI detector LS

γ γ

Electron (~1MeV)

Cherenkov light

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ZI COS pro to -type de te c to r

Purpose of Performance : 1) Energy resolution 2) BG reduction study using Cherenkov lights Demonstration : 1)

96Zr : 10g (same as NEMO-3)

with natural abundance of Zr. 2) Half life limits T1/2(0νββ) > 1.0 x 1022 years will be obtained , if no BG was found in 200 days’ measurement.

10-4 scale of ZICOS detector

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Simula tio n o f Hit pa tte rn o f Che re nko v

Simulated by EGS5 (kinetic energy 1.65MeV)

Np>3 Np>4 Np>5

e-

Co rre c tio n o f inc ide nt po sitio n o n PMT

tan dθmax=(s/2)/r s : radius of PMT surface r : distance between PMT and vertex position θ r Wider or narrower angle θ could be corrected by dθ .

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Average direction = Σ di di dθ

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Hit pa tte rn a fte r c o rre c tio n

Simulated by EGS5 (kinetic energy 1.65MeV) Np>3 Np>4 Np>5

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Ve rte x re c o nstruc tio n using c hi-sq ua re

Simple vertex reconstruction using multi-photon PMTs makes clusters around generated position, even though electron’s multiple scattering . Real (not proto-type) ZICOS detector will use not only hit pattern, but also light arrival time in order to reconstruct vertex correctly , so that much better vertex reconstruction resolution should be expected.

Np>3 Np>4 Np>5

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Ho w to se pa ra te Che re nko v a nd sc intilla tio n

Separation of scintillation and Cherenkov lights in PMT signal using waveform of FADC. C.Shaomin et al. arXiv:1511.09339 Cherenkov has a faster peak than scintillation.

 L

iquid sc intillator c ontaining Zr (ipr ac )4 has be e n de ve lope d for ZICOS e xpe r ime nt.

 Suc c e e de d to obtain L

iquid sc intillator with 10 wt.% c onc e ntr ation of Zr (ipr ac )4 has 48.7±7.1% for light yie ld to BC505 and 3.5±0.5% at 3.35Me V (assuming 40% photo c ove r age ) for e ne r gy r e solution.

 We ar

e de ve loping ne w te c hnique for a bac kgr

• und

r e duc tion using Che r e nkov light for ve r te x r e c onstr uc tion. (available for L S family like KL

• Ze n, SNO+, e tc )

 ZICOS se nsitivity : T

1/ 2 0ν > ~2×1026y; and <m ν> < 0.04-

0.06e V (QRPA) if both 58.5% e nr ic hme nt and BG le ve l at 1/ 20 × KamL AND- Ze n ac hie ve d.

 We will tr

y also Nd(ipr ac )3 be c ause lar ge r Q- value (3.67Me V) and twic e lar ge r natur al abundanc e (6% ).

 We ar

e now ope n for ne w c ollabor ator s.

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Summa ry

BACK UP

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E le c tro ma g ne tic iso to pe se pa ra tio n

@ ORNL

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Ba c kg ro unds a ro und 3.35Me V

214Bi contaminates

within 1m inner volume, but most

• f events could be

removed by Bi-Po tagging. If α particle may absorbed in films, we can not use tagging. 0νββ signal region for 96Zr

I.Shimizu@Neutrino2014

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Single peak could be used even in liquid scintillator.

source

Liquid scintillator

NaI detector PMT

Ba c ksc a tte ring me tho d

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Me a sure me nt o f Che re nko v lig ht

Comparison of light yields with

• r without SC-37 filter using

back scattering method.

50 deg

47deg 60Co

NaI detector LS

γ γ

Electron (~1MeV)

Cherenkov light

15%

Simulated by EGS5

10deg 30deg 50deg 70deg 90deg 110deg 130deg 150deg 170deg 190deg 210deg 230deg

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Cro ss se c tio n o f g a mma in a niso le

Most of few MeV range γs interact with anisole via Compton scattering.

Compton scattering

At least, one event could have Cherenkov hits.

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E ve nt dire c tio n a nd a ve ra g e PMT dire c tio n

No relation between event direction and averaged PMT direction was found . Clustered PMTs should be made by longest track within multiple scattering.

AT T E NUAT I ON L E NGT H OF ANI SOL E

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Attenuation length of scintillation light from POPOP (~450nm) was

• btained as ~6m.

No problem for radius

• f ZICOS detector.

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L ig ht yie ld o f sc intilla tio n in a niso le

Relative scintillation light yield of anisole is 9.8% to standard cocktail (due to difference of quantum efficiency of PMT)

300nm 400nm

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T ha llium-208 ra dia tio n b ra nc h

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L I GHT YI E L D COMPARI SON BE T WE E N BC505 AND ST ANDARD COCK T AI L

Light yield of BC505 and our standard cocktail (100mg PPO and 10mg POPOP solved in 20mL anisole) is almost same quality.

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E missio n a nd a b so rptio n spe c tra fo r so lve nt a nd so lute in sta nda rd c o c kta il

PPO absorbed most

• f emission lights from

anisole. Effectively the energy was transferred to the secondary scintillator.

E NE RGY SPE CT RA F OR SE VE RAL CONCE NT RAT I ON OF ZR(I PRAC)4

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Peak values decreased as a function of the concentration of Zr(iprac)4. Energy resolutions are also getting worth as a function of the concentration of Zr(iprac)4.

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RE COVE RY F OR ABI L I T Y OF L I GHT YI E L D AND E NE RGY RE SOL UT I ON

PPO helps recovering the light yield and the energy resolution. Confirmed our assumption and obtained optimized real cocktail (PPO 5wt.% POPOP 0.5wt.%)

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UV sha rp c ut filte r (F uji films)

400nm 500nm 600nm 700nm 90% 80% 50%

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Physic a l c o nsta nts o f L iq uid Sc intilla to r

LY of NaI(Tl) : 4×104 photon/MeV LY of BC505 : 1.2×104 photon/MeV

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Revealing the history of the universe with underground particle and nuclear research 2016 May 11, 2016

Na tura l ra dia tive U/ T h de c a y c ha in

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Pho to c o ve ra g e

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L ig ht yie ld a nd e ne rg y re so lutio n

Zr(ipcac)4 and Zr(etac)4 have almost same performance, but LY and Eres depend strongly on concemtration.

fitted fitted

PURI F I CAT I ON OF ANI SOL E

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Attenuation length of light from POPOP was

• btained as ~6m for

current liquid scintillator. Attenuation length will be recovered ~15m by same purification method as RENO with

• Al2O3. (Ref: H.Grubbs et al.,

Org.Mat. 1996 15,1518-1520)