double beta experiment using nuclear emulsions?

M. Dracos, Bologna, 01/09/2008 1

Double Beta experiment Double Beta experiment using nuclear emulsions?using nuclear emulsions?

?

Marcos DracosIPHC/IN2P3, Strasbourg


?

Double Beta DecayDouble Beta Decay

T 1/2 ~ 1019-1020 years !Observed for: Mo100, Ge76, Se82, Cd116, Te130, Zr96, Ca48, Nd150

allowed double beta

double beta without neutrino

dW-

W-d

u

e-

e-

u

_

_

dW-

W-d

u

e-

e-

u

_

T1/2= F(Q,Z) |M|2 <m>2-1

Phase space factor Nuclear matrix element

Effective mass:<m>= m1|Ue1|2 + m2|Ue2|2.ei1 + m3|Ue3|2.ei2

|Uei|: mixing matrix elements, 1 and 2: Majorana phases

5

L=2


Neutrino mass hierarchyNeutrino mass hierarchy

Goal of next generation experiments:~10 meV

Inverted hierarchy

Normal hierarchy

Degen

erate

Lightest neutrino (m1) in eV

| mee

| in

eV

Lower bounds!

m2

m12

m22

m32

Degeneratem1≈m2≈m3» |mi-mj|

Normal hierarchym3>>> m2~m1

Inverted hierarchym2~m1>>m3

?


Present detection techniques or Present detection techniques or under investigation under investigation

CalorimeterSemi-conductorsSource = detector

, E

Calorimeter(Loaded) Scintillator

Source = detector

,

Tracko-caloSource detector

isotope choice

Xe TPCSource = detector

,M

good energy resolution better background rejection

CUORE

CaF2(Pure)

CANDLES

NEMO3

EXO


IsotopesIsotopesIsotope Q(keV)116Cd116Sn 2804.74.282Se82Kr 2995.23.3100Mo100Ru 3034.86.396Zr96Mo 3350.03.5150Nd150Sm 3367.14.948Ca48Ti 4272.04.1

Bckg

sourcesthicknessmg/cm2)

82Se (0,93 kg)

isotopes used by NEMO3 experiment at Fréjus


The NEMO3 detectorThe NEMO3 detector

Sources : 10 kg, 20 m2

wire chamber(Geiger)

3m

energy and time of flight measurements

plastic scintillator blocks

2 electron tracks

+photomultipliers (Hamamatsu 3", 5")

expected sensitivity up to m~0.3 eV


Event ExamplesEvent Examples


ResultsResults932 g

389 days2750 even.

S/B = 4

82Se

82Se T1/2 = 9.6 0.3 (stat) 1.0 (syst) 1019 y116Cd T1/2 = 2.8 0.1 (stat) 0.3 (syst) 1019 y150Nd T1/2 = 9.7 0.7 (stat) 1.0 (syst) 1018 y96Zr T1/2 = 2.0 0.3 (stat) 0.2 (syst) 1019 y48Ca T1/2 = 3.9 0.7 (stat) 0.6 (syst) 1019 y

48Ca

background subtracted

Phase I + II693 days

T1/2() > 5.8 1023 (90 % C.L.) <m> <0.6-2.5 eVExpected in 2009T1/2() > 2 1024 (90 % C.L.) <m> <0.3-1.3 eV

100Mo( 7 kg )


Super NEMOSuper NEMO

• Improvements:– Energy resolution 15% E/E = 4% @ 3 MeV – Efficiency 15% 20 - 40% @ 3 MeV – Source x10 larger 7kg 100 - 200 kg

• Most promising isotopes– 82Se (baseline) or perhaps– 150Nd

• Aim: T1/2 > 2 x 1026 y M < 40 - 90 meV

R&D up to 2009, constructionbetween 2010 and 2013 (if approved)

source sheet


e

e

22 with emulsions with emulsions"veto" emulsion,

if needed(~50 m like in

OPERA?)

plastic base

"2" emulsionthick enough to detect up to 4 MeV electrons (density?)

beta source(~50 m in NEMO3

could be less for emulsions)


Tests in Nagoya using OPERA emulsionsTests in Nagoya using OPERA emulsionsA. Ariga, diploma thesis

50 m

electron spectrometer


Electron tracks in emulsionsElectron tracks in emulsions1 MeV e-

2 MeV e-

(A. Ariga and NIM A 575 (2007) 466)

simulation

simulation100 m


22 with emulsions with emulsions• NEMO3 surface: 20 m2

•Super-NEMO surface: 10x20 m2

• To cover the same isotope source surface with emulsions (both sides to detect the 2 electrons) we need an emulsion surface: 2x200=400 m2.

• Just for comparison, one OPERA emulsion has a surface of about 0.012 m2 and one brick 0.680 m2. So 400 m2 is about the equivalent of 600 OPERA bricks over 150000 (but not with the same thickness of course, taking into account the thickness this could be the equivalent in emulsion volume of about 25000 OPERA bricks).

• Use the same envelops like the OPERA changeable sheets by introducing at the middle of the two emulsions (or stack of emulsion sheets) a double beta source sheet.

• Keep all these envelops for some time (e.g. 6-12 months) in the experiment and after this period start scanning them one after the other. They could be replaced by new envelops during 5 years in order to accumulate something equivalent to what Super-NEMO could do: 5*400 year*m2

• Experiment volume: <5 m3 very compact experiment!


Previous tentativePrevious tentative

• 1.28 g 96Zr (powder)• source thickness: 180 m• total exposure time: 3717 hours• scanned surface for electron pairs: 10 mm2

• estimated total efficiency: 18%

Conclusion:• T1/2(96Zr)>1017 years,• decrease the thickness of the isotope layer,• use low radioactivity emulsions,• scanning speed has to considerably be increased

(automatic scanning needed).


0.003

0.003

0.1

0.11.2

7.0

4060

140

700

0.001

0.01

0.1

1

10

100

1000

cm2 / h

TS(1994) NTS(1996) UTS(1998) SUTS(2006) SUTS(2007-)

Scanning Power Roadmap

1stagefacility

CHORUS DONUT OPERA

Emulsion scanningEmulsion scanning• How much time is needed to make a full

scan of 2000 m2 (full scan in all volume not needed, just follow tracks present in the emulsion layer near the isotope foil)?

• If the Japanese S-UTS scanning system is used with a speed of 50 cm2/hour, for one scanning table: 25 m2/year (200 working days/year). By using 16 tables and extracting 100 m2/3 months (1 year exposure at the beginning and putting back new emulsions with the same isotopes), this finally will take less than 5 years (as Super-NEMO).

• Probably the emulsion thickness needed to detect these electrons will need more scanning time and the speed would be significantly less than 50 cm2/h. On the other hand, scanning speed increases with time…

Nakamura sanNufact07


Pending questionsPending questions

• Energy resolution for NEMO: 15% for 1 MeV electrons•Required for Super-NEMO: lower than 8%

• Emulsion experiment energy resolution: ??? • Overall reconstruction efficiency for NEMO: 15-18%

•Required for Super-NEMO: >30% • Emulsion experiment reconstruction efficiency: ??• Minimum electron energy (~0.5 MeV?, 0.200 MeV for NEMO3), will

greatly influence the total efficiency.• Afforded background?• Possibility to take thinner isotope sheets (60 m for NEMO3) and have

better energy resolution (but also more scanning for the same isotope mass, find good compromise).


Possible isotopes to be usedPossible isotopes to be used

For emulsions the electron detection threshold cannot be so low than NEMO3 (200 keV, low density material gas+plastic scintillator) utilisation of high Q-value isotopes>3 MeV•advantage: low background, high efficiency•problem: low abundance


Feasibility studiesFeasibility studies

• Reconstruction efficiency: by counting the number of reconstructed electrons from both energy lines after scanning (this would help to tune the algorithms).

• Electron threshold: the reconstruction efficiency for both electrons (mainly those at 482 keV) would give a good idea about the threshold.

• Energy resolution: by counting the associated grains to the track, by measuring the track range.• Afforded background: perform the above tests with different backgrounds.

• Needed• scanning tables,• low radioactivity lab (Gran Sasso, Baksan, Fréjus…),• thick emulsions (refreshed in low radioactivity lab).

emulsion sheets 0.6 mm thick(3-4 layers)

207Bi source with well known activity(EICe-=976, 482 keV)


LimitationsLimitations• high multiple scattering for low energy electrons• de/dx fluctuations• bremsstrahlung gammas (energy lost)• lost -electrons• electron backscattering

better to use low density emulsions?

0.7 MeV e-

(10 tracks)

d=2.7 g/cm3

(Geant 3.2)


Extra IdeasExtra Ideas

ee

decreasing density

(25 m layers)

to minimize the emulsion thickness and better energy resolution at the end

of the track

e

e

emitter in powder (diluted in an emulsion layer)

better vertex and energy reconstruction?

(few isotopes are anyway in powder form)

M. Dracos, Bologna, 01/09/2008 21Electron + N ’s 208Tl (E = 2.6 MeV)

Electron crossing > 4 MeV Neutron capture Electron + delay track (164 s) 214Bi 214Po 210Pb

Electron – positron pair B rejection

BACKGROUND EVENTS OBSERVED BY NEMO-3BACKGROUND EVENTS OBSERVED BY NEMO-3and rejection in emulsionsand rejection in emulsions

end of tracks easily recognised in emulsions rejection

alpha tracks easily recognised in emulsions rejection

no vertex or very good vertex resolution in emulsions rejection

cannot be rejected in absence of magnetic field good emulsion shielding


E1+E2= 2880 keV

Run 2220, event 136.604, May 11th 2003

track(delay = 70 s)214Po 210Pb

214Bi 214Po decay IN THE GAS

-like event due to Radon from the gas (NEMO3)-like event due to Radon from the gas (NEMO3)


NEMO3 main background NEMO3 main background configurationsconfigurations

Proportion of types of events in raw data:

Type of event Rate (mHz)

1 e, 0 600

1 e, N

150

ee pairs 110

Crossing e 80

event 5.4 mHz


ConclusionConclusion• Technology allows now the investigation about observation of

double beta decays using nuclear emulsions• To prove the experiment feasibility few questions have to be

answered:• what is the energy resolution?• what is the afforded background?• what is the overall efficiency?

• The above questions could be answered with relatively low investment.


ENDEND

double beta experiment using nuclear emulsions?

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