Erice, 20.9.2009Kai Zuber 1

Status of the COBRA Experiment

K. Zuber, TU Dresden

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Contents

• General introduction

• Low background issues

• Pixel activities

• Summary and Outlook

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COBRA

Use large amount of CdZnTe Semiconductor Detectors

large array of CdZnTe detectors

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

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COBRA collaboration

Supporting institutes: Jagellonian University (Poland), Los Alamos Nat. Lab. (USA)

TU Dresden TU Dortmund

Laboratori Nazionali del Gran Sasso

University of Bratislava

Washington University at St. Louis

Mat. Res. Centre FreiburgUniversity of ErlangenUniversity of Hamburg

More welcome

University of Jyvaskyla

University of La Plata

Czech Technical University Prague JINR Dubna

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Isotopes

70Zn 0.62 1001 ß-ß- 114Cd 28.7 534 ß-ß- 116Cd 7.5 2809 ß-ß- 128Te 31.7 868 ß-ß- 130Te 33.8 2529 ß-ß- 64Zn 48.6 1096 ß+/EC 106Cd 1.21 2771 ß+ß+ 108Cd 0.9 231 EC/EC 120Te 0.1 1722 ß+/EC

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

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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

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Background

COBRA

beyond 2.614 MeV background a priori much lower

S. Pirro, Milano

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It‘s all about background

1024 pixel, pixel size: 625 m

Background from: natural radioactivity, cosmogenic produced radioisotopes,

cosmic rays, neutrons

energy measurement only energy measurement and tracking

two options

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Gran Sasso (Italy)

COBRAGERDA

CUORE

It‘s all about background reduction

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COBRA Set-up at LNGS

Designed for 64 detectors (at hand)

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Results: Cd-113

We have more than 10 independent measurements

now...

first time theoretical model based on nuclear

structure calculation(thanks to J. Suhonen)

4-fold non-unique beta decay (1/2+9/2+)

first time histogram of 1016 yrs half-life measurements

Q-value:

J. V. Dawson et al., Nucl. Phys. A 818,264 (2009)

Spectral shape fits better with unique 3-fold forbidden than non-unique transition

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Results: 0νDBD

based on 18 kg days of data,J.V. Dawson et al., Phys. Rev. C 80,025502 (2009)

six half-life limits above 1020 years, one world best, six limits within factor 3 of world best, coincidence analysis ongoing

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Current status

Background at 2.8 MeV around 5 counts/keV/kg/yr

still options to improve

Data taking with red crystals finished, now running 4 (8) clear painted detectors in a nitrogen atmosphere

Cd-116peak range

Major background: Red paint and radon in the air

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The solid state TPC

energy resolution tracking

pixelated CdZnTe detectors

• massive background reduction• positive signal identification

Semiconductor Tracker

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Pixelisation

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.

• idea: massive background reduction by particle identification

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Pixel detectors

Pixel detector with 200 m pixels

(10000 pixel) produced!

1024 pixel, pixel size: 625 m

two options: Timepix , CZT ASICs

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Option 1: ASICs for CZT

Detectors: 2x2x0.5 cm3

One 32x32 pixels sent for bonding to 1024 channel ASIC

Second one 55x55 pixels sent for bonding to 2048 channel ASIC

64 pixel detectors

Installation at LNGS winter 2009

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Option 2: Timepix Medipix2 coll.

• Timepix Si, 300μm thick (data shown)

• TimePix CdTe detector

1mm thick Both systems

256x256 Pixel, 55μm pitch, 1.4x1.4 cm2

1mm

Myon candidate

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snapshot...214Bi alpha-beta coincidence candidate

Unfortunately I can‘t show you a double beta event ...

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Event pool surface-u/g

It reacts on environment, ie. notcompletely dominated by internal

background

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Particles....

Alphas Betas Muons

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A nice muon...

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

Yes we can! B. Obama

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Needed Sensitivity

50 meV

T1/ 2 M t /E B

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KING COBRA - Below 50 meV

116Cd

116In

116Sn

A real time low-energy solar neutrino and Supernova experiment?

Threshold energy: 464 keV

7Be contribution g.s. alone: 227 SNU

= 14s

K. Zuber, Phys. Lett. B 571,148 (2003)K Balasi, P. Divari, T.Kosmas, J. Suhonen, E. Ydrefors,K. Zuber, in prep.

e

ee

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

Down to 10 meV you might be ...

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Summary• COBRA is a rather new approach making use of

CZT room temperature semiconductors.

• First background sources have been identified and removed, working towards larger array (64), lower background. Major upgrade spring in 2010.

• The solid state TPC (semiconductor tracker) can be the major and unique step forward. First underground datataken.

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