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The COBRA Experiment. Henric Krawczynski (Washington Univ. in St. Louis) for the COBRA Collaboration. Introduction to COBRA. CZT Detectors. Backgrounds & Sensitivity. Plans and Requirements. COBRA Collaboration (Zuber et al.). University of Sussex. University of Bratislava.

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the cobra experiment
The COBRA Experiment

Henric Krawczynski (Washington Univ. in St. Louis)for the COBRA Collaboration

  • Introduction to COBRA.
  • CZT Detectors.
  • Backgrounds & Sensitivity.
  • Plans and Requirements.
cobra collaboration zuber et al
COBRA Collaboration (Zuber et al.)

University of Sussex

University of Bratislava

University of Warwick

University of Liverpool

Rutherford Appleton Lab.

University of Jyvaskyla

University of Birmingham

University of York

TU Dresden

University of La Plata

University of Dortmund

MRC Freiburg

Technical University Prague

Laboratori Nazionali del Gran Sasso

Still expanding.

Washington University in St. Louis

Idaho National Laboratory

Observer status: University of Surrey (UK), University of Hamburg (Germany), Jagellonian University (Poland), Louisianna State University (USA), Technical University Dresden (Germany), Daresbury Laboratory (UK), Los Alamos National Laboratory (USA).

double beta decay of 116 cd


Double Beta Decay of 116Cd

116Cd Q-value: 2.809 MeV.

Natural 116Cd abundance: 7.49% 116Cd (+ 130Te?) enrichment.

F. Simkovic, ILIAS DBD meeting, Valencia 2006, see also:E. Caurier and J. Menendez and F. Nowacki and A. Poves, nucl-th/0709.2137

cobra strengths
COBRA Strengths
  • Source = detector.
  • Semiconductor.
  • Room temperature.
  • Modular design.

• Industrial development of CdZnTe detectors.

  • 116Cd Q-value: 2.809 MeV.
  • Sub-mm Tracking („Solid state TPC“).
cobra cadmium telluride o neutrino double beta research apparatus


COBRA (Cadmium-Telluride O-neutrino double-Beta Research Apparatus)

Based on Arrays of CdZnTe

semiconductor detectors:

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





czt detectors energy resolution
CZT Detectors - Energy Resolution

1.522cm36 cm3 = 35 gr.

Zhong, Krawczynski et al.

status of cobra prototype experiment

Status of COBRA Prototype Experiment

64 Detector Array at Gran Sasso National Laboratory:

Oct. 2007

64 detectors operational!

preliminary results with 4x4 detector layer
Preliminary Results With 4x4 Detector Layer

About 8 kg days (x2 more than published, T. Bloxham et al. Phys. Rev. C, 76, 025501 (2007)

recent improvements substantial background reduction
Recent Improvements: Substantial Background Reduction
  • Problems:
  • Passivation paint.
  • Radon.

Expected background index: 150  < 1 cts keV-1 kg-1 yr-1.

background estimate

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

<1 neutron per year in 420 kg experiment.

D. Stewart et al., NIMA, 571, 651 (2007).

Background Estimate

Simulations of external, internal, cosmogenic, and  backgrounds: background index: 10-4-10-3cts keV-1 kg-1 yr-1.

cobra sensitivity

50 meV

COBRA Sensitivity

Background free:

Background limited:

czt detectors spatial resolution
CZT Detectors - Spatial Resolution

1.3mm pixel pitch

Washington Univ.

50 m squares

Development of ≥0.5 cm thick detectors with 200 micron spatial resolution and multiplexed readout.

additional background rejection through event tracking
Additional Background Rejection Through Event Tracking
  • Massive BG reduction by particle ID , 200m pixels (see e.g. Bloxham & Freer, NIMA, 572,2, 722 (2007)):




  • eg. Could achieve nearly 100% identification alphas and of 214Bi beta events (214Bi  214Po  210Pb).
cobra a solid state experiment with unique capabilties
COBRA: a solid state  experiment with unique capabilties!

Next steps (continued R&D):

  • Reduce background for 64-detector experiment.
  • Detector development:
    • Radiochemical cleaning (extraction chromatography).
    • Use of Cd enriched to >90% with 116Cd.
    • 200 m spatial resolution.
  • Full tradeoff study coplanar grid vs. pixelated detectors, test of shielding and background suppression methods in test beams and underground.

Towards a large-scale experiment:

  • 2010/2011: Finalize design.
  • 2012: Construction of experiment in layers of 40x40 detectors.

DUSEL Requirements:

  • COBRA: compact, no crygenic cooling, little liquid chemicals.
  • Multiple campuses advantageous.
  • Weekly seminar to engender interaction of scientists from different disciplines.
results from background simulations
Results from Background Simulations