0ν - Double β Decay Experiment- DCBA -

Norio TamuraG.S. of Science and Technology, Niigata Univ.

• Introduction• 0ν-Double β Decay• DCBA Experiment

2ν-Double β Decay

Double β Decay with two neutrinos• Higher order process of a single beta decay• Positive measurement for some nulei• Important for the determination of

the Nuclear matrix element.

ye

ye

2113.011.02/1

7676

182/1

100100

1001.077.1;22SeGe

102.24.16.7;22RuMo

×±=+−+→

×+−=+−+→

+−

τν

τν

d

d

e-

e-

u

u

W

W

νν

N2ν and N0ν are sensitive to internal spin/Isospin structure of the nucleus

　　by Ejiri etal.

⇒　 N0ν　?

( ) ( ) ( )*

2**

m

fmNmiNfiN∆

→⋅→=→ νν

ν

0ν-Double β Decay (1)

Most typical 0ν-Double β Decay is　　

　N(Z,A) → N’(Z±2 ,A) + 2e

For the observation of this process, it is necessary thatSingle β Decay is inhibited !

-+

n

n

A-2

e-

e-νp

p

Se7624

As7623

Ge7622

1+

2-

0+

0+

ββ

Inhibit

Meaning of Detection of 0ν-Double β Decay

Double β Decay with no neutrinos• Definite direct evidence of Majorana neutrino

Violation of Lepton Number• Right handed interaction( Non-zero mass? )• The neutrino is left handed at one vertex,

while it is right handed at the other.

　Massive neutrino ( 0+ 0+ )　　and / or 　V+A interaction （ 0+ 0+ , 2+）

　　New physics beyond the Standard Model !

d

d

e-

e-

u

u

W

W

⇒

V-A

V+A

L

R

ν=ν

Neutrino mass and Lifetime of 0ν-Double β Decay

Rate of DβD

　Meff：　Effective mass of neutrino（ Particle physics）

　N：　　Nuclear Matrix Element(Inc. Phase Vol.)　If “no right handed current” and “small mass”

　　　Mm：　Mass eigen-value　　　UMNS(em)：　Mixing matrix element　　　ω(em)：　　Phase factor　

( ) ( ) effmmMNSm

eff MMMemUemM ≥⇒=

⇓

∑ 2ω

Example:Assume standard value for N,

and use an experimental lifetime

then　　Mm～1 eV .

Sufficiently realistic value !

Ge76

[ ] [ ] 21

24 yr011V1

⋅≅

Geeff eM τ

[ ] ,year1024Ge76 ≥τ

( )21

0

21

2022

01

νββ

νββνββ

τ⋅=

=⇒⋅=

NN

AMNMA effeff

Lifetime of 0ν-Double β Decayand Nuclear Matrix Element (1)

( )νββ

νββτ

τ0

20

1⋅

=⇔⋅= −

NMNM effeff

Important to know the nuclear matrix elementto determine the neutrino mass.

N2β2ν　⇒　 N2β0ν ?　Progress in theoretical calculation　Calculation may be more reliable for 0ν mode rather

than for 2ν mode. ⇒ See next pageMore importantly, • 　Discovery of 0ν-Double β Decay

Discovery of Majorana neutrino• 　Mass is the next things to be determined

Lifetime of 0ν-DβD

and NME (2)

Calculated half-lives by several models

(PDG2000)

0ν-Double β Decay (2)0ν-Double β Decay with Majoron(s)　Majoron：

Comes from Violation of B(baryon number)-L(lepton number) Symmetry

　　　・　Different Eββ dist. from 2ν-mode one

82Se(’87 UCI)：τ1/2 > 4.4x1020 yr (90%CL)Majoron coupling constant　gee <=(2-30)x10-4

76Ge(’93 Heidel.)：τ1/2 > 1.66x1027 yr (90%CL)Majoron coupling constant 　gee <1.8x10-4 (90%CL)

d

d

e-

e-

u

ν

u

W

W

Mν

ββ0ν

ββ2ν ββ1M

Q

0ν-Double β Decay (3)

SUSY-inspired 0ν-Double β Decay　R-parity Violationd

d

e-

e-

u

u

u～

u～

γ～Z～g～

And other processes

76Ge：　2.5x1023 yr

105GeV105GeV

40 GeV300GeV104GeV

150 GeV950GeV103GeV

440 GeV3 TeV100GeV

Lower boundon mu for the Zino+Photinocase

Lower boundon mu for the gluino case

Gaugenomass ～ ～

Can give strong limits⇒

Search for Double β Decay (1)1. Geo-chemical measurement　Measurement of daughter nuclei, noble gas, accumulated for more

than 109 years in the ore.　(1) The ore must be a closed system. (no In/Out of daughter nuclei)　(2) Independent determination of the oldness of the ore.

(3) Double β decay is the predominant process for the production of the daughter nuclei in the ore.

　★No separation between 0ν and 2ν !

Assumption

41Kirsten832.60±0.28>800

130Te→130Xe128Te→128Xe

36Bernatowicz922.7±0.17200±400

130Te→130Xe128Te→128Xe

Kawashima930.039±0.00996Zr→96Mo31Takaoka960.79±0.10130Te→130XeDocument(PDG2k)Half-life（0ν+2ν）1021yearNuclide

Search for Double β Decay (2)

2. Radio chemical method　☆Decay from radio-active nucleus:

Measurable in shorter term, 2-3yrs

3. Direct measurementEvent by event measurement of double β decay　☆ Discrimination between 0ν，2ν events

Less assumption, Suppression of background　★Difficult to get sufficient statistical significance

Enrichment and large amount of source

39Turkevich912.0±0.6238U→238PuDocument(PDG2k)Half-life（0ν+2ν）1021yrNuclide

Search for Double β Decay (3)Progress of half-life measurements　　3x1015(“48)⇒ 5x1023(“87) ⇒ 2～3x1025(“00)

• Active source：　Source = Detector　⇒　CaF2，Ge，GdWO4，Xe• Passive source： Source = Detector

1) TPC(Time Projection Chamber)2) ELEGANTs(Drift Chamber+Scintillation Counter+NaI)　　⇒2～3x1022yrs3) Use of 136Xe, source, gas as chambers, TPC etc. 　　Multi-cell proportional counter⇒Gran Sasso　　High Pressure proportional counter⇒Baksan(2n-mode)　　136Xe gas（ 180cm3 ）for TPC ⇒ Gottard tunnel　　136Xe gas（ 10kg ） for TPC（proposal; ITEP ） 　⇒　>1024 yr?

Search for Double β Decay (4)4) Scintillation Detector： CaF2， GdWO45) NENO detector（Frejus underground lab.）3 dims. tracking＋Cal.　　 100Mo， 116Cd， 82Se， 130Te， 96Zr， 150Nd，etc.　　⇒　<0.3-0.7 eV in 2005？6) Semiconductor Detector：　　・Sandwitch of 100Mo and Si-detector（⇒>4.4x1022を得た。）

　　・ Ge (Natural)，76Ge (Enriched)，Heidelberg-Moskow etc.7) Cryogenic Detectors：Use of bolometer　　 TeO2⇒CUORE detector （1000 TeO2 bolometer ）

1025yr in 10 years8) Kamland：By adding liq. 136Xe

⇒ achieves the sensitivity of <mn>～0.15eV ?9) GENIUS： 76Ge ⇒<mn>～0.01eV！！？

And may others

Search for Double β Decay (5)

25Desilva9726Desilva97

TPCTPC

2ν;0ν;

150Nd150Nd>1.2(90%CL)

21Alston9722Barabash97

Si(Li)γ in HP Ge

2ν;0ν +2ν;

100Mo92Mo>0.81

19Luescher9819Luescher98

Xe TPCXe TPC

0ν;2ν;

136Xe136Xe

>440 (90%CL)>0.36 (90%CL)

18Alessandrello9818Alessandrello98

Cryog. Det.Cryog. Det.

0ν;0ν;

130Te128Te

>56 (90%CL)>17 (90%CL)

16Arnold9916Arnold99

NEMO-2NEMO-2

2ν;0ν;

96Zr>1.0

15Aalseth9917Baudis99

Enriched HP GeEnriched HP Ge

0ν;0ν;

76Ge>8000(90%CL)>16000 (90%CL)

Document(PDG2k)MothodModeNuclideτ1/2(1021yr)

002.0021.0 008.0004.0 ±+

−

( ) 36.7 2.24.1 −+

− E

( ) 368.075.6 37.042.0 −±+

− E

And may others

Evidence of 0ν-Double β Decay (1)

“Evidence !!?? for Neutrinoless Double Beta Decay”Heidelberg-Moscow Double Beta Decay Experiment :

Modern Physics Letters A 16 (2001) 2409-2420

Enriched(86%) High Purity Ge-detector at Gran Sasso U.L.Aug.1990-May2000; 54.9813kgy

( )ν227676 ++→ −eSeGe

Sum spectra of the 76Ge detectors

“All” “Single Site Events”( ) ( )CLT %951007.3580.0 250

21 ×−=ν ( ) ( )CLT %951033.1875.0 25021 ×−=ν

Evidence of 0ν-Double β Decay (2)

Analyzed by two methods1) Bayesian method and 2) PDG methods

“All”

“Single SiteEvents”

Evidence of 0ν-Double β Decay (3)

Results

Evidence of 0ν-Double β Decay (4)Impact of this result

Characteristics of 0ν-Double β Decay

Tβ(1)+Tβ(2)= Q-value(const.)

Best limit obtainedby HP Ge detector is

yeSeGe 252/1

7676 106.1;2 ×>−+→ τ

DCBA Experiment

Drift Chamber Beta Analyzer　・Search for 0ν-Double β Decay　　　Of course, 2ν-Double β Decay , too.Collaborators:N.Ishihara, T.Inagaki, T.Ohama, K.Omata, S.Takeda, Y.Yamada;

INPS, High Energy Accelerator Research Organization (KEK)

S.Miyamoto, Y.Nagasaka; Hiroshima Institute of Technology

F.Fujiwara, Y.Kato, T.Nishi, N. Tamura; Niigata Univ.

S.Kitamura; Tokyo Metropolitan University of Health Science

R.Ito, T.Emura, Y.Kunimi; Tokyo Univ. of Agriculture and Technology

Y.Sakamoto; Rikkyo Univ.

Sources of double β decay

31.78687.77・10242.63・1024128Te→128Xe

0.1874,27148Ca→48Ti

2.83,3505.30・10231.08・101996Zr→96Mo17.41,1453.97・10256.93・102294Zr →94Mo9.22,9956.03・10231.09・102082Se→82Kr

5.63,3673.37・10227.37・1018150Nd→150Sm8.92,4792.21・10244.64・1021136Xe→136Ba

34.52,5334.89・10231.84・1021130Te→130Xe

5.62,2881.36・10245.25・1021124Sn→124Te7.52,8024.87・10236.31・1019116Cd→116Sn9.63,0341.27・10241.13・1018100Mo→100Ru

7.82,0402.33・10242.99・102176Ge→76Se

P[%]Qββ[keV]T0ν1/2 <mν>2 [y・eV2]T2ν

1/2[y]Nucleus

DCBA Experiment(1)Source： (Neodymium)Expected life time:

• Relatively short life time (expected)• Large Q-value ( =3.367MeV)

・ Relatively easier measurement especially for a drift chamber

224222

.

202/1

1818.

22/1

eVyr1005.1oreVyr1037.3

yr100.6oryr1037.7

⋅×⋅×=⋅

××=

calc

calc

mT

T

νν

ν

Nd15060

DCBA Detector (1)

4×10243.8×1022Expected sensitivity

T1/2lim[yr]

～ 100 (Assumed)～ 100 (Assumed)Energy resolution [keV]

～ 0.1 (Assumed)-> 60 for 2.8-3.4MeV

～0.1(Assumed)-> 200 for 1.0-3.0MeV

Background [keV-1yr-1]

Nd2O3

(～90%, 150Nd)Natural Nd

(5.6%, 150Nd) Source

4.5×10253.8×1022Number of Nucleus0νββ2νββMain target mode

0.70.4Detection EfficiencyDCBA-ⅡDCBA-Ⅰ

DCBA Detector (2)

DCBA-I

DCBA-II

DCBA-T DCBA-T

¼ model of DCBA-IFor engineering testStructureGas, Source plateResolutionR&D of

DAQ & Analysisetc.

DCBA-T　Structure of the Endplate

Electric Field Simulation with Garfield

equi-potential line

(cm)

source plate

Anode wire Cathode wire

(cm)

DCBA Detector (3)　　　Structure of the Detector　　　　　　　　　Drift Chamber part

Fig. by Y.Kato

Thickness of Nd-source plate35mg/cm2 (50µm t)

Expected sensitivity

1yr

10yrs

DCBA Detector (4)

• Detection of 2 electrons with a Drift Chamber• 3-dim. Tracking

x-coordinate : Drift timey-coordinate : Hit wire positionz-coordinate : Charge division

• Wave-shape measurement by a Flash ADCAllow time- & charge-measurement for multiple hitsby looping tracks

　⇒　Determination of energy and track of electrons.

• Veto-counters: Veto of incoming charge particlesCalibration of the chamber

DAQ0: Hardware Configuration　

TKO/FADC

Board ComputerOS VxWorks

VME/SMP

Board ComputerOS Solaris

DCBA

OS PC Linux

ControlEvent

Display(PAW)

100 MbpsEthernet

100 MbpsEthernet

sampling rate : 50MHz1kword / ch. 1word : 8bit

160 ch.

Temporary DAQSystem for Test run

By T. Nishi; NU

Study on Backgrounds

Major Background sources1) 2ν-double beta decay

“Good resolution” and “single track energy cut”N. Ishihara etal.: Nucl. Instr. and Meth. A 443 (2000) 101-107

2) Background by gammasSurrounding materialsCosmic ray

3) Background by β decay followed by an internal conversion electron from Radon & thoron contamination in the air

Monte Carlo Simulation

Study on Backgrounds from γs(1)

Processes producing 2-electrons by a gamma

1C2M1Ph2M

1C2C1C2Ph

1P2M

Study on Backgrounds from γs(2)

Results of Simulation: GENBOD+EGS4

# of hit γ s is 106

Sum energy spectra of the 2e events Contributions of the five processesEe>0.5MeV, Σ Ee<4MeV

Study on Backgrounds from γs(3)• γ-ray from materials in DCBA-T (Measured with a Ge-detector)

208Tl0.090.09--2,645

214Bi7.820.011.016.801,772

40K3.370.140.582.651,463

214Bi0.290.010.28-1,120

228Ac1.240.031.21-911

27Mg / 56Mn18.190.05-18.14844

214Bi5.750.081.324.35609

208Tl1.140.081.06-583e+-annihilation6.740.400.296.05511

(x106 counts/year)(keV)γ-sourceTotalBGDG10AlEnergy

Study on Backgrounds from γs(4)

ΣEe spectra ΣEe spectra

ΣEe spectra

110m depth + 10.2cm Pb

Background from surroundings and cosmic ray

Background from radioactivematerials

Normalized to DCBA-T

Ntot=712 for DCBA-I

200 for 2ν1/5

Not a problem for 0ν

2ν(DCBA-I) : 56k

0ν (DCBA-II) : 500k

200

60

1/1,000

1/10,000

@Surface

Simulation Study on Events and Backgrounds -

By R. Ito; TUAT

• Event simulationSimulation events made by Geant4.Development of tracking program.

Vertex, Momentum resolution

• Background studiesComparison of 0νmode events

with background events of 　　　　　　214Bi and 208Tl.

Simulation Study(2)0n event simulated　　　　　　　 by Geant4

β1

VTX

β2

yy

x

B

VTXβ1

β2

x

z

VTX

β2

β1

y

z zx

Simulation Study(3)Program flow

Simulation using Geant4

PurposesEnergy resolution 　Tββ distributionVertex point resolution

Data flow of simulation

Simulation Study(4)- Analysis -

• 3 dim. tracking　　Spiral fitting　　　 x-y plane: circle fitting　　　　 parameters ; origin & radius　　 z direction: sin-wave fitting　　　parameter ; Period (Amplitude is fixed)

• Correction for the energy loss in the material　　1)Measured range of the electron Calculate ∆T (∆T-Range)　　2)Measured energy of the electron Calculate average ∆T

(∆T-Energy)

Simulation Study (5) - Energy resolution -

dT = Tcalc - Tvertex

Even

t N

umbe

r RMS = 0.3657MeV

∆T-Energy• 0νmode events.

10000 events.Calculated from 5hits.

3330 events

dT(MeV)

Simulation Study (7) - Tββ distribution -

Tββ = T1 + T2

10000 events.Calculated from 5hit.

3330 events

Total Energy

Even

t N

umbe

r RMS = 0.5020MeV

Q=3.37MeV

∆T-Energy• 0νmode events.

Tββ(MeV)

Simulation Study (8) - Vertex resolution -

Even

t N

umbe

r RMS = 1.308mm

• 0νmode events.

dV = Ycalc - Yvertex

dV(mm)

10000 events.Calculated from 5hit.

3330 events

Simulation Study (9) - 214Bi Decay channels -

0.0499Total

0.00351.421.866

0.00970.6092.665

0.003690.6091.894

0.0020.8111.863

0.02620.6091.542

0.004820.6091.421

B.R.(%)TC.E.(MeV)Tβ(MeV)• 0νββ

• 214Bi “ββ”

3254.050001627

0 ==effνββη

25 10887.5

105887 −

→ ×==effBi ββη

Simulation Study (9) - Background simulation-1 -

3.27MeV 4.99MeV

Source of Background214Bi and 208Tl

208Tl β + I.C.(e-)

214Bi β + I.C. (e-)

Simulation Study (9) - 214Bi sum energy distribution -

Q=3.37MeV

Cut

• For Eββ>2.6 MeV

28.00 =effνββη

6102.1 −→ ×=eff

Bi ββη

Simulation Study (9) - 208Tl Decay channels -

0.1532.611.808

0.6630.591.807

1.35Total

0.0660.871.526

0.011772.611.525

0.01940.591.524

0.0132.611.293

0.006580.591.292

0.4140.511.291

B.R.(%)TC.E.(MeV)Tβ(MeV)

• 0νββ

• 208Tl “ββ”

3254.050001627

0 ==effνββη

25 10438.4

104438 −

→ ×==effTl ββη

Simulation Study (9) - 208Tl-08 background events -

Q=3.37MeV

208Tl sum energy distribution

Simulation Study (9) - 0νmode and 208Tl : single electron distribution -

Even

t N

umbe

r

208Tl100000events

(4503events)

Even

t N

umbe

r

0ν

T(MeV)T(MeV)

Simulation Study (9) - 208Tl-08 single electron distribution -

Even

t N

umbe

r

T(MeV)

Beta-decay 1.80MeVConversion electron

2.61MeV

Cut Cut

• For Eββ>2.6 MeV

and 0.8<Eβ<2.2 MeV

19.00 =effνββη

5105.3 −→ ×=eff

Tl ββη

Estimation of Background- 214Bi and 208Tl-08 -

For example, at Oto Cosmo-ObservatoryRadon density ～20Bq/m3

Air in the chamber gas ～250 ppm (←O2～50 ppm )

VDCBA-T=7.2x10-6m3 (sensitive region)

⇒　Radon～1.44x10-4Bq　　　　　⇒　 214Bi : 4.54x103/y x1.2x10-6=5.22x 10-3 events/y

⇒　 208Tl : Thoron density ～1/10 of radon (Frejus U.L.)4.54x102/y x3.5x10-5=1.6x 10-2 events /y

150Nd(0.015 mol in DCBA-T) : 8.0x10-3 events/y for <mν>=0.39eVwith enriched source ⇒　12x10-2 events/y

Simulation Study (9) - Summary -

• Resolution of Energy-Sum, Tββ , in 0ν mode :　　　　RMS = 0.50MeV at 0.33 eff.

• 214Bi background：　　　　Could be eliminated by cut in Tββ distribution

In addition, elimination with α(delayed)from following decay

double buffer in new FADC

• 208Tl background：　　　　Could be eliminated by cut in Tβ distribution

Present Status of ＤＣＢＡ (1)Engineering test run by DCBA-T(1/4 model)

Chamber in fabrication

Data Acquisition

Present Status of ＤＣＢＡ (2)- Chamber & Magnet (1) -

Present Status of ＤＣＢＡ (4)

- Magnet: Field mapping -

Uniformity of <1%in all sensitive region

V

Wire # =y Drift time=x

x

y

Time reference

Present Status of ＤＣＢＡ (5)

- Data (Cosmic ray); (1) -

Track of a cosmic ray particleFast drift speedwith saturation

Present Status of ＤＣＢＡ (5)- Data (Cosmic ray)　(2) -

Time ( x 20 ns.)Wire No.

(x 0.04 V)

With slow gas

Wir

e N

o.

Time ( x 20 ns.)

Present Status of ＤＣＢＡ (5)- Data (Cosmic ray); Drift Velocity 　(3) -

200 400 600 800 1000Time ( x 20 ns.)

coun

ts

Ar 89% CO2 10% CH4 1%

200 400 600 800 1000Time ( x 20 ns.)

coun

ts

He 60% CO2 30% CH4 10%306

Present Status of ＤＣＢＡ (6) –

–Position resolution -

（Ｚ）

（Ｘ）

XZ

Y

200mm

600mm0

0

･Signal･Noise

Y

Y

Present Status of ＤＣＢＡ (6)– X-Position resolution -

0 5-5

0 5-5 [mm]

[mm]

14 layers with large correction

Entries : 15476

Efficiency : 87.3%

RMS : 0.999 mm

26 layers with small correction

Entries : 22872

Efficiency : 79.5%

RMS : 0.680 mm

Present Status of ＤＣＢＡ (6)- Z-Position resolution -

500 mm-500 0

500 mm-500 0

500 mm-500 0

No CorrectionThreshold: 16

Amp. Gain CorrectedThreshold: 80

Amp. Gain CorrectedThreshold: 16

Entries:38348

RMS:142.0mm

Entries:38348

RMS:130.1mm

Entries:15751

RMS:83.12mm

500

500

500

Present Status of ＤＣＢＡ (7) –- Measurement with 207Bi (1)-

･ 207Bi source on the source plate･ γ decay followed by an internal conversion･ Energy: 0.5, 1.0, 1.7 MeV･ Self Trigger

･Momentum measurement in a magnetic field

λ e－

B

r = 49.0mm

cosλ= 0.908P = 1.30 MeV/c

T = 0.881 MeV

（Ｚ）

（Ｘ）

（Ｙ）

200mm

600mm0

0（Ｙ）

Present Status of ＤＣＢＡ (7) –- Meaurement with 207Bi (2)-

Present Status of ＤＣＢＡ (8)- Data (in magnetic field；Bi-source）(1) -

Track by electronfrom 207Bi

Looping electron

Present Status of ＤＣＢＡ (8) -Data (in magnetic field；Bi-source）(2) -

Knock-on electron?By cosmic muonPair Creation !

ＤＣＢＡ：Plan(Near future-1)

1. Analysis, Correction, Calibration etc.　1) Measurement of Drift speed and get “correction”

(Now in progress, by E.of March)　2) Establish of Tracking

(Now in progress, by E.of March)　3) Calibration of Momentum with 207Bi-source

Measurement of Momentum Resolution

Test run with Nd source plate (Next Fiscal Year)

2. Modification of Chamber　For more uniform electric field more uniform drift speed

ＤＣＢＡ：Plan(Near future-2)

3. Upgrade of Data Acquisition System

　1) Replace FADCs with newly developed FADC in CPCI standard.

(Now, in production)　2) Upgrade of DAQ

CPCI, Multi-CPU,Embedded LinuxJavaDAQ(Now, in progressby E. of next fiscal year)

Summary

1. 0ν double beta decay : Majorana neutrino, Neutrino-mass etc.

2. Present situation: Near(?) the finding of finite lifetime of 0ν DBD or found?

3. DCBA: Drift Chamber Beta Analyzer150Nd, Now testing with DCBA-T

Test the performance of the chamber⇒ ImprovementDCBA-I: 2ν modeDCBA-II: 0ν mode