COBRA A new Approach to -Decay UK HEP Forum, Abingdon, May 11 th, 2003 Daniel Muenstermann University of Dortmund COBRA.

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A new Approach to -Decay

UK HEP Forum, Abingdon,

May 11th, 2003

Daniel Muenstermann

University of Dortmund

www.COBRA.physik.uni-dortmund.de

COBRA

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AWhat 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)

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AWhy is (0)-decay an opportunity?

It can determine the nature of the neutrino (Majorana vs. Dirac particle).

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Leptoquarks, Rp violating SUSY

It might help to disclose other modifications of weak processes like right-handed weak currentsn

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pL=2 , Eff. Majorana masses

It can reveal the rest-mass of the electron neutrino on an absolute scale.

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AMore on ++ decays

There are 3 possible modes:++: (A,Z) (A,Z-2) + 2 e+ (+2e) (Q - 4 mec2)+/EC: e- + (A,Z) (A,Z-2) + e+ (+2e ) (Q - 2 mec2)EC/EC: 2 e- + (A,Z) (A,Z-2) (+2e) (Q)

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++-ellipsoid RRLRRLLL JjJjJjJjH int

Heidelberg-Moscow evidence

++ decays are dominated by right-handed weak currents !

EC/EC is preferred byphase space!

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AWhy is CdZnTe a favourable material?

116Cd: Q-Value at 2.8 MeV, above all naturally occuring -lines

130Te: has large natural abundance (34 %)sits in „compton gap“ of 208Tldirect comparison to geochemical experiments

106Cd: ++-decay at 2.7 MeV possible, but +/EC or EC/EC decays preferred by phase space

It contains 9 -isotopes, among them

potential for a background-free experiment where mass limits grow linear inmeasurement time!

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AWhy 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

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AReality strikes back: Current Limitations of CdZnTe

Crystal growth: large quantities: 1 cm3 cubesselected detectors: 16 cm3 cubes

Large hole trapping: Use selective electron readout

Therefore: Instead of few large crystals (Heidelberg-Moscow = 1-3 kg) build an array of small detectors

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ACOBRA

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

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AEarly 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

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AEarly Achievements of COBRA

Calibration spectrum with 228Th:

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Low energy partof the spectrum:

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

Spectrum with and without shield:

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AThe 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

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ATime 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

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Aad 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)

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ASummary 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...

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ALast Words

Join the party!

Collaborators most welcome!