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A new Approach to  -Decay

COBRA. A new Approach to  -Decay. UK HEP Forum, Abingdon, May 11 th , 2003 Daniel Muenstermann University of Dortmund www.COBRA.physik.uni-dortmund.de. What is COBRA about?. COBRA aims to study -decays of Cd, Zn and Te isotopes. deals with and evolves low-level physics.

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A new Approach to  -Decay

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  1. COBRA A new Approach to -Decay UK HEP Forum, Abingdon, May 11th, 2003 Daniel Muenstermann University of Dortmund www.COBRA.physik.uni-dortmund.de

  2. What is COBRA about? COBRA • aims to study -decays of Cd, Zn and Te isotopes. • deals with and evolves low-level physics. • is currently based in • the UK (Univ. of Oxford, K. Zuber, spokesperson) • Germany (Univ. of Dortmund) • Italy (LNGS)

  3. It might help to disclose other modifications of weak processes like right-handed weak currents • It can reveal the rest-mass of the electron neutrino on an absolute scale. n p n p e e n p n p Leptoquarks, Rp violating SUSY L=2 , Eff. Majorana masses Why is (0)-decay an opportunity? • It can determine the nature of the neutrino (Majorana vs. Dirac particle).

  4. <> Heidelberg- Moscow evidence <m>(eV) ++-ellipsoid More on ++ decays There are 3 possible modes: ++: (A,Z)  (A,Z-2) + 2 e+ (+2e) (Q - 4 mec2) +/EC: e- + (A,Z)  (A,Z-2) + e+ (+2e ) (Q - 2 mec2) EC/EC: 2 e- + (A,Z)  (A,Z-2) (+2e) (Q) EC/EC is preferred by phase space! ++ decays are dominated by right-handed weak currents !

  5. potential for a background-free experiment where mass limits grow linear in measurement time! Why is CdZnTe a favourable material? It contains 9 -isotopes, among them 116Cd: Q-Value at 2.8 MeV, above all naturally occuring -lines 130Te: has large natural abundance (34 %) sits in „compton gap“ of 208Tl direct comparison to geochemical experiments 106Cd: ++-decay at 2.7 MeV possible, but +/EC or EC/EC decays preferred by phase space

  6. Why are CdZnTe semiconductor detectorsadvantagous devices? • good energy resolution (compared to scintillators) • high density compared to gaseous ionisation detectors, large source masses • no cooling needed with CdZnTe • industrially available, commercial development in progress • in our case: source = detector • particle tracking is possible with pixel-devices (solid-state-TPC) • operation in cryogenic mode possible

  7. Reality strikes back: Current Limitations of CdZnTe • Crystal growth: large quantities: 1 cm3 cubes selected detectors: 16 cm3 cubes Therefore: Instead of few large crystals (Heidelberg-Moscow = 1-3 kg) build an array of small detectors • Large hole trapping: Use selective electron readout

  8. COBRA Idea: Build an array of CdZnTe detectors. Characteristics of COBRA: • minimal use of construction material close to the detectors necessary as • no cooling is needed • source = detector • 9 -isotopes measured simultaneously

  9. Early Achievements of COBRA • First „ad-hoc“ efforts with commercial 0.5 cm3 detector and MCA-based readout: • Veto and shield are working • 2 publications with new and improved limits: Muenstermann and Zuber: „An alternative Search for the Electron Capture of 123Te“, J. Phys. G: Nucl. Part. Phys. 29 (2003) B1-B4 Kiel, Muenstermann and Zuber: „A Search for various Double Beta Decay Modes of Cd, Te and Zn Isotopes“, nucl-ex/0301007, to be published in Nucl. Phys. A

  10. Early Achievements of COBRA Calibration spectrum with 228Th:

  11. Low energy part of the spectrum: Spectrum with and without shield: Early Achievements of COBRA • Background at 2.8 MeV: ~ 5 ·10-4 events/(keV g d) • 208Tl-peak at 2.6 MeV visible. Contamination in detector or surroundings?  Build own low-level mounting

  12. The Status of COBRA There is a 2 x 2 array of 1 cm3 detectors with • custom-built preamplifier electronics • (still) CAMAC-based event-by-event readout • passive copper and lead shielding • a plastic-scintillator based cosmic muon veto

  13. Time schedule • Next week: relocation of the setup into the Gran Sasso laboratory • Autumn 2003: First results due, decision about funding of 4 x 4 prototype due • Spring 2004: scalable 4 x 4 prototype and scalable readout electronics operational • Winter 2004: proposal for a competitive 0-decay based on CdZnTe

  14. ad hoc: COBRA compared to‘An Ideal Experiment‘ by Steve Elliot • large mass: CdZnTe detectors are available with m < 100 g  Array of detectors • good source radiopurity: Work in progress, no serious cosmogenic background • demonstrated technology: Again, work in progress • natural isotopes: Yes • source = detector: Yes • energy resolution (< 3 %): Yes • ease of operation: Yes, but ask us in autumn... • large Q value: Yes • event reconstruction: With pixel detectors (3D)

  15. Summary and Outlook COBRA • uses commercially available CdZnTe detectors to measure 9  isotopes simultaneously • has already improved 6  limits with comparably little effort • will move from the surface to the Gran Sasso underground lab for improved low-level measurements next week • is up to now a rather small collaboration, so...

  16. Last Words Join the party! Collaborators most welcome!

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