COBRA

Kai Zuber University of Sussex

5th SNOLAB Workshop, 22.8.2006

Contents

• Introduction• Current status of

COBRA• The 64 detector

array• Longer term

planning• Summary

C0BRA

Use large amount of CdZnTe Semiconductor Detectors

Array of 1cm3

CdTe detectors

K. Zuber, Phys. Lett. B 519,1 (2001)

COBRA 2006

some are missing...

Isotopes

Zn70 0.62 1001 ß-ß-Cd114 28.7 534 ß-ß-Cd116 7.5 2805 ß-ß-Te128 31.7 868 ß-ß-Te130 33.8 2529 ß-ß-Zn64 48.6 1096 ß+/ECCd106 1.21 2771 ß+ß+Cd108 0.9 231 EC/ECTe120 0.1 1722 ß+/EC

nat. ab. (%) Q (keV) Decay mode

COBRA: CdZnTe semiconductors

++ - modes

• (A,Z) (A,Z-2) + 2 e+ (+2e) ++ • e- + (A,Z) (A,Z-2) + e+ (+2e ) +/EC

• 2 e- + (A,Z) (A,Z-2) (+2e) EC/EC

Important to reveal mechanism if 0 is discoveredEnhanced sensitivity to right handed weak currents

(V+A)

n

n

p

pe

eIn general:

Q-4mec2

Q-2mec2

Q

Double charged higgs bosons,R-parity violating SUSY couplings,leptoquarks...

Advantages

• Source = detector

• Semiconductor (Good energy resolution, clean)

• Room temperature

• Tracking („Solid state TPC“)

• Modular design (Coincidences)

• Industrial development of CdTe detectors

• Two isotopes at once

• 116Cd above 2.614 MeV

Contents

• Introduction• Current status of

COBRA• The 64 detector

array• Longer term

planning• Summary

The 2x2 prototype

4 naked 1cm3 CdZnTe

more than 4.3 kg x days of data,stopped March 2006

Setup installed at Gran Sasso Underground Laboratory

NeutronsWorry (if not enriched in 116Cd): 113Cd (nth,)114Cd

MCNP simulation of the full set-up

Physics - 113Cd

T1/2 = (8.2 ± 0.2 (stat.) +0.2-1.0 (sys)) 1015 yrs

113Cd one of only three 4-fold forbidden -emitters known in nature

C. Goessling et al., Phys. Rev. C 72, 064328 (2005)

Latest Limits

worldbest

PRELIMINARY

Contents

• Introduction• Current status of

COBRA• The 64 detector

array• Longer term

planning• Summary

The first layer

Installed at LNGS about three month ago

Coincidences – 214Bi

T1/2 = 162 ± 19s

Can exclude backgrounds through timing coincidence214Bi 214Po 210Pb

7.7MeV alpha half-life = 164.3s

Beta withendpoint 3.3MeV

Strategies

• We started a long term R&D with eV-Products to find another passivation (they have alternatives)

• Alternative providers not using the paint(Freiburg Material Research Centre)

New passivation

Raw data

Very preliminary: At least a factor 10 better, lot of construction workaround COBRA at LNGS, no coincidences, no nitrogen flushing...

Cd116

Contents

• Introduction• Current status of

COBRA• The 64 detector

array• Longer term

planning• Summary

Back of the envelope

1/2 = ln2 • a • NA• M • t / N (T) ( Background free)

50 meV implies half-life measurements of 1026-27 yrs

1 event/yr you need 1026-27 source atoms

This is about 1000 moles of isotope, implying 100 kg

Now you only can loose: nat. abundance, efficiency, background, ...

Cd116- Matrix elements

<m>=0.4eV

V. Rodin et alV. Rodin et al., nucl-th/0503063, Nucl Phys. A 2006nucl-th/0503063, Nucl Phys. A 2006

Sensitivity

50 meV

2 - decay

€

F =8Q(ΔE /Q)6

me

= 3.7*10−10

S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002

Energy resolution important semiconductor

Fraction of 2 in 0 peak:

Signal/Background:

4331

02/1

22/1 ==

TT

FBS

yrsT 1922/1 102.3 ×=

yrsT 2602/1 102×=

2 is ultimate, irreducible background

Energy Resolution

• Only electron signal read out (CPG technology)• Possible improvements: cooling, new grids• Better detectors are available

E = 1.9% @ 2.8MeV

=2.9% @ 662keV

Resolution of =0.8% at 2.8 MeV

Dimension it right!

116Cd

116In

116Sn

A real time low-energy solar neutrino experiment?

Threshold energy: 464 keV

7Be contribution gs. alone: 227 SNU

= 14s

K. Zuber, Phys. Lett. B 571,148 (2003)

e

ee

Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd

The solid state TPCEnergy resolution Tracking

Pixellated CdZnTe detectors

• Massive backgroundreduction• Positive signal information

Pixellisation - I• Massive BG reduction by particle ID , 200m pixels (example simulations):

• eg. Could achieve nearly 100% identification of 214Bi events (214Bi 214Po 210Pb)

.

00

1-1.5mm1-1.5mm

~15~15mm

3 MeV 3 MeV

7.7MeV life-time = 164.3s

Beta withendpoint 3.3MeV

= 1 pixel, and = several connected pixel, = some disconnected p.

Pixellisation - II Tests of 16×16 1.6mm pixel detectors

crystal

ASIC readout

122 keV

136 keV

Pixellated detectors

3D - Pixelisation:

We have two 2D pixellated detectors running

Nobody said it was going to be easy, and nobody was right

George W. Bush

Shielding and Veto• Simulated LNGS neutron flux

• ~3x10-7 counts/year/kg/keV in the crystals.

• <1 neutron per year! <1 neutron per year! (in 64000 detectors)

Size = 18.4 m3

Mass = 64964 kg

D. Stewart et al., submitted to Nucl. Inst. Meth. AD. Stewart et al., submitted to Nucl. Inst. Meth. A

detectorsdetectors

And many more things going on

Red = 24°C

Blue = 10°C

T-measurement

Pulse shape analysis

Thermal n-capture

PL: Zn-content

nm

Summary• COBRA plans to use a large amount of CdZnTe

semiconductors for double beta searches• Collaboration of about 25 people established• Currently preparing a 64 detector array (about 0.5 kg),

installation at LNGS started spring 2006• Design changed to allow easy upgrade to larger scales• Work on signal enhancer and pixellated detectors has

started• New german grant application successful, UK and US

grant applications in preparation• Around 2009/10 TDR for large experiment