Status of COBRA

K. Zuber, Univ. of SussexBlaubeuren, July 2007

COBRA

Use large amount of CdZnTe Semiconductor Detectors

Array of 1cm3

CdZnTe detectors

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

Isotopes

Zn70 0.62 1001 ß-ß- Cd114 28.7 534 ß-ß- Cd116 7.5 2809 ß-ß- Te128 31.7 868 ß-ß- Te130 33.8 2529 ß-ß- Zn64 48.6 1096 ß+/EC Cd106 1.21 2771 ß+ß+ Cd108 0.9 231 EC/EC Te120 0.1 1722 ß+/EC

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

COBRA: CdZnTe semiconductors

++ - 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...

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

COBRA collaboration

University of Surrey (UK), University of Hamburg (Germany),Jagellonian University (Poland),Louisianna State University (USA)

University of Dortmund

University of Sussex

Laboratori Nazionali del Gran Sasso

University of Warwick University of BirminghamUniversity of Liverpool

University of York

Rutherford Appleton Laboratory

University of Bratislava

Washington University at St. Louis

Material Research Centre Freiburg

More welcome

University of Jyvaskyla

COBRA at LNGS

COBRASince april 20072004-march 2007

worldbest

First COBRADouble beta results

T. Bloxham et al., submitted

PertinaxCopper CZTWax

Based on 4 detectors, total of 4.34 kg x days

Redesigned prototype

Delrin holder and kapton foilScalable design for larger masses

The 64 array - the next step4x4x4 detector array = 0.42 kg CdZnTe semiconductors

Zur Anzeige wird der QuickTime™ Dekompressor „Cinepak“

benötigt.

The 64 detector arrayThe next step towards a large scale experiment,Scalable modular design, explore coincidences

Worldwide largestexperiment of 1cm3

CPG detectors

Mass factor 16 higher,about 0.42 kg CdZnTe

Physics: - Can access2ECEC in theoreticallypredicted region-Precision measurement of 113Cd- New limits70 detectors in total available/characterised

The first layer

Installed at LNGS in april 2006

The first layer - some spectraCd-113 beta decaywith half-life of about 1016 yrs

The first layer - Coincidences

Just starting to analyse/understand the power of that..

Preliminary

Coincidences around Det 7

Example:3-coincidence

Powerful tool!!!

Coincidences

Example: 130Te 1st excited state

1. 1 Detector with 2530 keV2. 1 Detector with 1994 keV3. 2 Detectors (One with

1994 keV, one with 536 keV))4. 2 Detectors (One with

1994 keV, two sum up to 536 keV)

€

130Te→130Xe∗+ 2e− + γ (536keV )

Have performed a search for mode 3 in 4.2 kg x days and foundno event !

Ex. 2: 106Cd 0ECEC with 2 photons

Signature: Triple coincidence : Middle detector (X-rays),two more detectors in a line with

E and (Q-X-rays- E )

€

2e−+106Cd→106Pd + 2γ

Very likely background free!

F. Simkovic et al.

12

New passivation (4 detectors)

Sample measurements at ICP-MS @ LNGSsuggest improvement of about 3 orders of magnitude

Monte Carloexpectation

Paint contribution at 2.8 MeV: about 0.2 counts/keV/kg/yr

Major background so far: Red paint on detector surface

New passivation

Very preliminary: At least a factor 10 better, lot of construction workaround COBRA at LNGS, no coincidences, no nitrogen flushing...

Around 10 counts/keV/kg/yr

The solid state TPCEnergy resolution Tracking

Pixellated CdZnTe detectors

• Massive backgroundreduction• Positive signal information

Pixellisation - I• Massive BG reduction by particle ID , 200m pixels (example simulations):

• eg. Could achieve nearly 100% identification of 214Bi events (214Bi 214Po 210Pb).

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.

Rejection power of pixels

First look on rejection power

Suggests a background reduction of 1000!

T. Bloxham, M. Freer,Nucl. Inst. Meth. A (2007)

Likelihood using:

-Number of pixels

- spatial separation

- energy loss (dE/dx)

Nobody said it was going to be easy, and nobody was right

George W. Bush

A. Poves (yesterday): A. Poves (yesterday): 116116Cd most convenient, TCd most convenient, T1/21/2 = 2.9 x10 = 2.9 x102626 for for 50meV 50meV

Uncertainties in nuclear matrix elements, example 116Cd

V. Rodin et alV. Rodin et al., nucl-th/0503063, Nucl. Phys. A 766,107 (2006)nucl-th/0503063, Nucl. Phys. A 766,107 (2006)

Sensitivity (conservative)

50 meV

€

T1/ 2 ∝ M × t /ΔE × BAssume BG limited from beginning

2 - decay

€

F =8Q(ΔE /Q)6

me= 3.7*10−10

S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002

Energy resolution (FWHM) important semiconductor

Fraction of 2 in 0 peak:

Signal/Background:

4331

02/1

22/1 ==

TT

FBS

yrsT 1922/1 102.3 ×=

yrsT 2602/1 102×=

2 is ultimate, irreducible background

Energy Resolution

• Only electron signal read out (CPG technology)• Possible improvements: cooling, new grids• Better detectors are available

E = 1.9% @ 2.8MeV

=2.9% @ 662keV

Resolution of =0.8% at 2.8 MeV

COBRA for solar neutrinos - King COBRA

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)

e

ee

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

SNO+ - A 150Nd double beta decay experiment

SNO+- 1st collab. meeting

More welcome!

Summary• COBRA is a new approach to double beta

decay using CdZnTe• Follows two lines: Background

identification and reduction (LNGS) and development of high resolution pixel-CZT

• Two major items for 2007:Finish the 64 array at LNGS in new locationTwo high resolution pixel detectors

• Progress is fast....

And many more things going on

Red = 24°C

Blue = 10°C

T-measurement

Pulse shape analysis

Thermal n-capture

PL: Zn-content

nm