K. Zuber, Uni. Sussex

Status of COBRA

IDEA Meeting, Zaragoza 7 Nov. 2005

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 - The peopleC. Gößling, H. Kiel, D. Münstermann, S. Oehl, T. Villett

University of DortmundJ. Dawson, C. Montag, D. Polzaird, C. Reeve, J. Wilson, K. Zuber

University of Sussex

+ further interested institutes

Laboratori Nazionali del Gran SassoM. Junker

University of WarwickP.F. Harrison, B. Morgan, Y. Ramachers, D. Stewart

T. Bloxham, M. FreerP. Seller

B. Fulton, A. Smith, R. Wadsworth

A. Boston, P. Nolan

University of Birmingham

University of Liverpool

University of York

Rutherford Appleton Laboratory

COBRA 2005

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

Level schemes

Quite a few lines...

++ - 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...

Neutrino mass vs. right handed currents++++ +++∝ RRLRRLLL JjJjJjJjH ληκint

€

λ,η <<1

<m> (eV)

<λ>

Possible evidence

M. Hirsch et al., Z. Phys. A 347,151 (1994)

EC/ß+

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

Running periods

• Running at LNGS since February 2004• Scheme driven by money/manpower • CAMAC DAQ - 4 detector prototype• CAMAC DAQ - 4 detector prototype mod.• VME DAQ - 4 detector prototype modified

Background

• Cosmogenics

• neutrons

116Cd (Q=2805 keV)

• 2

113Cd (nth,)114Cd

Measurement: E. Porras et al., NIM B 111, 325 (1996)

• Alphas, Betas, Gammas

• muon induced neutrons

2 - decay

+ Tracking option

€

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:

43310

2/1

22/1 ==

TT

FBS

yrsT 1922/1 102.3 ×=

yrsT 2602/1 102×=

2 is ultimate, irreducible background

The 2x2 prototype

4 naked 1cm3 CdZnTe

more than 2.5 kg x days of data

Setup installed at Gran Sasso Underground Laboratory

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

MCNP simulation of the full set-up

Calibration

2.4% energy resolution at 2614 keVMuch better ones availableA little bit of cooling helps

Comparison of measurements

0.5 cm3, surface, no shielding

„old“ prototype, LNGS, no shielding

„old“ prototype, LNGS, shielding, no veto

The background modelInput: Pertinax (grid, base), detectors, paint and copper

Currently limiting background: Passivation paint on detectors

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)

Redesigned prototype

Delrin holder and kapton foilScalable design for larger masses

New versus old prototype

Measuring time: 2630 hours , about 0.71 kg x days, Det1 only

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., nucl-ex/0508016, acc. by Phys. Rev. C

First results

T1/2 close to 1020 years obtained

70Zn 1.3 x 1016 2.9x1017

116Cd 8.0 x1018 1.1x1019

130Te 3.3x1019 8.2x1019

106Cd 0+ EC 3.8x1017 1. 6x1018

64Zn 0+ EC 2.8x1016 2.6x1017

120Te 0+EC 2.2x1016 9.3x1016

0

NPA723

NPA 723

Current

Current

EC-modes

H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A 723,499 (2003)

Current results are preliminary

CoincidencesAim: Coincidences among crystals should significantly reduce gamma background

About 0.2 % ofevents are coincidences

Array too small to prove power of coincidences Larger Array

5 10 15 20 25 30

5

10

15

20

25

30

x

y

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

2000keV

2614 keV gamma (MC)

Contents

• Introduction• Current status of

COBRA• The 64 detector

array• Longer term

planning• Summary

The 64 detector arrayAim for next 2 years: The next step towards a large scale experiment,Scalable modular design, explore coincidences

Include:CoolingNitrogen flushing

Mass is factor 16 higher,about 0.5 kg CdZnTe

Physics: - Can access2ECEC in theoreticallypredicted region-Precision measurement of 113Cd- New limitsAll detectors are at Dortmund

Signatures - +/EC

High granularity

A lot of patterns,interesting to investigate

Contents

• Introduction• Current status of

COBRA• The 64 detector

array• Longer term

planning• Summary

The solid state TPC

Single electron spectra

Angular correlationcoefficient

Introduce tracking properties by using segmentedor pixellated electrodes and pulse shape analysis

First own measurementsTwo detectors: 4x4 pixel , 2mm x 2mm16x16 pixel, 1.6 mm x 1.6 mm

- plot Source location

Two pixel events

Pixellated detectors

3D - Pixelisation:

Solid state TPC

Nobody said it was going to be easy, and nobody was rightGeorge W. Bush

Back of the envelope

T1/2 = ln2 • a • NA• M • t / N (T) ( Background free)

50 meV implies half-life measurements of 1026-27 yrs1 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, ...

Dimension it right!

116Cd

116In

116Sn

A real time low-energy solar neutrino experiment?

Threshold energy: 464 keV

7Be contribution g.s. alone: 227 SNU

= 14s

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

eee

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

Sensitivity

50 meV

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), to be installed at LNGS end of 2005• Design changed to allow easy upgrade to larger scales• Work on signal enhancer/active veto and pixellated

detectors has started• Progress is fast

Einstein was right