Contents. General Introduction Low background activities Pixel activities Summary and Outlook. Kai Zuber

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1 Contents General Introduction Low background activities Pixel activities Summary and Outlook

2 COBRA Use large amount of CdZnTe Semiconductor Detectors Large array of CdZnTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)

3 COBRA collaboration TU Dresden TU Dortmund Material Research Centre Freiburg University of Erlangen Washington University at St. Louis Czech Technical University Prague University of Bratislava University of Jyvaskyla University of La Plata JINR Dubna Laboratori Nazionali del Gran Sasso More welcome Supporting institutes: University of Hamburg (Germany), Jagellonian University (Poland), Los Alamos Nat. Lab. (USA)

4 Isotopes nat. ab. (%) Q (kev) Decay mode Zn ß-ß- Cd ß-ß- Cd ß-ß- Te ß-ß- Te ß-ß- Zn ß+/EC Cd ß+ß+ Cd EC/EC Te ß+/EC

5 Advantages Source = detector Semiconductor (Good energy resolution, clean) Room temperature Modular design (Coincidences) Two isotopes at once Industrial development of CdTe detectors 116 Cd above MeV Tracking ( Solid state TPC )

6 Background COBRA S. Pirro, Milano Beyond MeV background a priori much lower

7 It s all about background Background from: natural radioactivity, cosmogenic produced radioisotopes, cosmic rays, neutrons Two options Energy measurement only Energy measurement and tracking 1024 pixel, pixel size: 625 µm

8 Gran Sasso (Italy) It s all about background reduction GERDA COBRA CUORE

9 COBRA Set-up at LNGS

10 Results: Cd fold non-unique beta decay (1/2 + 9/2 + ) First half-life result published as C. Goessling et al., PRC 72:064328,2005 First time theoretical model based on nuclear structure calculation (thanks to J. Suhonen) We have more than 10 independent measurements now...

11 Cd-113 First time histogram of yrs half-life measurements Half-life: Q-value: Spectral shape fits better with unique 3-fold forbidden than non-unique transition J. V. Dawson et al., Nucl. Phys. A 818,264 (2009)

12 Results: 0 DBD Six half-life limits above years, one world best, six limits within factor 3 of world best, coincidence analysis and analysis on colourless data ongoing based on 18 kg days of data, J.V. Dawson et al., arxiv: , acc. by Phys. Rev. C

13 The power of coincidences.. Example: 130 Te 130 Xe + 2e + γ(536kev ) 1. 1 Detector with 2530 kev 2. 1 Detector with 1994 kev 3. 2 Detectors (One with 1994 kev, one with 536 kev)) 4. 2 Detectors (One with 1994 kev, two sum up to 536 kev) Should lead to massive background reduction, Results?????? Analysis ongoing

14 Measured spectrum Data taking with red crystals finished, now running 4 (8) clear painted dets. Cd-116 peak range Background at 2.8 MeV around 5 counts/kev/kg/yr

15 Needed Sensitivity T 1/ 2 M t /ΔE B 50 mev

16 KING COBRA - Below 50 mev Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd Down to 10 mev you might be... A real time low-energy solar neutrino and Supernova experiment? e Threshold energy: 464 kev ν e 116In e 7Be contribution g.s. alone: 227 SNU 116Cd τ = 14s 116Sn K. Zuber, Phys. Lett. B 571,148 (2003) K Balasi, T.Kosmas, P. Divari,KZ, subm.

17 The solid state TPC Semiconductor Tracker Energy resolution Tracking Massive background reduction Positive signal identification Pixelated CdZnTe detectors

18 Pixelisation Idea: Massive background reduction by particle identification α= 1 pixel, β and ββ= several connected pixel, γ= some disconnected p. Beta with endpoint 3.3MeV 7.7MeV α life-time = 164.3µs

19 Pixel detectors Two options: Timepix, CZT ASICs 1024 pixel, pixel size: 625 µm Pixel detector with 200 µm pixels (10000 pixel) produced!

20 Option1: ASICs for CZT 64 pixel detectors Detectors: 2x2x0.5 cm 3 One 32x32 pixels sent for bonding to 1024 channel ASIC Second one 55x55 pixels sent fo bonding to 2048 channel ASIC Installation at LNGS autumn 2009

21 Option 2: Timepix Timepix Si, 300µm thick (data shown) TimePix CdTe detector 1mm thick, 256x256 Pixel, 55µm pitch, 1mm 1.4x1.4 cm2 Myon candidate

22 snapshot Bi alpha-beta coincidence candidate Unfortunately I can t show you a double beta event...

23 Event pool It reacts on environment, ie. not completely dominated by internal background

24 Particles... Alphas Betas Muons

25 A nice muon...

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

27 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 Would be interesting to learn more about signatures of double EC/EC and beta+/ec modes! Positron energy spectra etc. The solid state TPC (semiconductor tracker) can be the major and unique step beyond existing double beta experiments