Upgrade and progess on the COBRA double beta detector
Sudbury, 26. August 2010
Kai Zuber
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
- Introduction to COBRA- Current experimental
status- Physics results- The pixel option- COBRA Upgrade- Summary
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
COBRA
Use large amount of CdZnTe Semiconductor Detectors
K. Zuber, Phys. Lett. B 519,1 (2001)
Focus on 116Cd
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Technical University Dresden Technical University Dortmund
Laboratori Nazionali del Gran Sasso
University of Bratislava
Washington University at St. Louis
Material Res. Centre FreiburgUniversity of Erlangen-NürnbergUniversity of Hamburg
University of Jyvaskyla
University of La Plata
Czech TechnicalUniversity Prague
JINR Dubna
COBRA collaboration
More welcome ?Other institutes: Louisiana State University, University of MIchigan
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
K. Zuber
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
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
• 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
Advantages
K. ZuberSudbury, 26. 08.2010 SNOLAB 2010
Beyond 2.614 MeV background a priori much lower
Background
S. Pirro, Milano
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
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
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Setup at Gran Sasso Lab
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
LNGS spectrum
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Results: Cd-113
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)
Deviations with theory at lower energies
K. Zuber
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
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Coincidence events
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
The power of coincidences..
130Te 130Xe 2e (536keV )
Leads to massive background reduction,but at the moment low efficiencyLimits obtained not yet competitive with single detector results-> planned upgrade
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Background at 2.8 MeV around 5 counts/keV/kg/yr !
Data taking with 16 red crystals finished, about 18 kg*d statisticsMajor background: Red paint on surface, radon
116Cdpeak region
Measured spectrum
Actions: Colourless painting (4 + 4 detectors, nitrogen atmosphere with radon trap)
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Region of 116Cd peak
Region of interest – Raw data
Data cleaning , analysis ongoing
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Idea: Massive background reduction by particle identification
200 μm pixel simulation
For example Bi-214 :Time coincidence of both
Alpha
Electron 3 MeV
200 μm pixel simulation
COBRA - Pixel
Space and time coincidences possible
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Pixel size
(130Te)
Reasonablerange
For 200 m 130Te and 116Cd would hit about 7-10 pixel
K. Zuber
20x20x5 mm3 systems8x8 pixels (running at LNGS Jan. –May 2010)32x32 pixel system100x100 pixel system
Timepix system:14x14x0.3 mm3 Si ( 2 systems)14x14x1 mm3 CdTe (2 systems)256x256 systems128x128 systems
World largest CZT detector = 36 gramscollaboration with Zhong He (Univ. of Michigan)
20x20x15 mm3
11x11 pixel systemUp to 40 slices in z by pulse informationRunning at LNGS from Sep. 2009-Jan. 2010One system running in Felsenkeller Lab
since Sep. 2009, one running at LNGSsince May 2010, before Modane
COBRA – Pixel CZT
Sudbury, 26.08.2010 SNOLAB 2010
K. Zuber
Latest development on CZT
36 gram detector,6 times larger than current COBRA detectors
preliminary
Pixelated in 11x11,Can be sliced in zup to 40 slicesdue to drift time
Polaris system (U Mich)
K. Zuber
Polaris system
The power of pixels!
Together with University of Michigan (group Zhong He)
Sudbury, 26.08.2010 SNOLAB 2010
Running at LNGS from Sep. 2009-Jan. 2010
K. Zuber
No survivor after 125 days of data taking!!! Corresponds to a background between 2700-3000 keVof 0.9 counts/keV/kg/yr
Detector not tuned for low background
Polaris system
116Cd peakregion
Sudbury, 26.08.2010 SNOLAB 2010
K. Zuber
Timepix
It reacts on environment, ie. notcompletely dominated by internalbackground
55 μm pixel Si Timepix device
K. Zuber
A nice muon...
A nice muon
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Timepix
Electrons
Particle identification as background reduction tool works!
256x256 pixels, 55m
MuonsAlphas
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Picture show
NO event in 117.5 days in energy range between 2.7 and 3 MeV which looks like 1(2) electrons
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Idea: Massive background reduction by particle identification
200 μm pixel simulation
Bi-214 =Time coincidence of both
alpha electron
alpha
electron
Alpha
Electron 3 MeV
200 μm pixel simulation
55 μm pixel real event
COBRA - Pixel
K. Zuber
Nobody said it was going to be easy, and nobody was right. George W. BushYes we can! B. Obama
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
COBRA Upgrade 2010/11
Upgrade to 64 CZT 1 cm3 detectors, about 0.42 kg (all detectors at hand)Single grid readout , i.e. pulse shaping Improved shielding , readout (new DAQ) , material selectionActive veto (CsI), strongly enhances physics potentialAim : Background below 1 count/keV/kg/yr
Running CZT in LSciProduce enriched CZT detectorsRunning a larger scale Polaris system and pixel systems
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Pulse shape
Much more information in pulse shape
CPG detector works like a Frisch grid in wire chambersP. Luke , IEEE Trans. NS 42, 207 (1995)
60Co pulse
Experiment
TCAD simulation
Single site event Multiple site event
J. McGrath et al. , NIM A 615,57 (2010)
Modification of preamps necessary... DoneFirst new preamps and two FADCs installed at LNGS this week
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
COBRA Upgrade
Aim : Improve excited state and positron decay sensitivity by factor 10-30
Done for :NaI, CsI , BGO, CdWO4
Exploring various readout concepts
Note: Can tolerate some impuritiesbecause of coincidencerequirement
128Te 1st excited state116Cd 1st excited state
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Material screening (DLB)
Factor of 1000 reduction with respect to unshielded
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
Bare crystals in LScintillator I
K. Zuber
Bare crystals in LScintillator II
K. Zuber
Crystal growing
Crystal growing done within the collaboration
Preparation for growing enriched crystal/detector
Sudbury, 26.08.2010 SNOLAB 2010
K. ZuberSudbury, 26.08.2010 SNOLAB 2010
King Cobra
Measurement of 50 meV neutrino mass would require about 400 kgof CZT, isotopically enriched in Cd-116
Shielding must be ableto reduce background to less than 10-3 events /kg/keV/yr
Plan is to have TDR by end of 2012
K. ZuberCambridge, 14.07.2010 IWORID2010
Conclusion
COBRA is a promising next generation experiment to explore double beta decay of Cd-116. First scientific results have been obtained , major upgrades planned in the nextyearUnique option would be the semiconductor tracker (solid-state TPC)in form of a pixel CZT, first measurements are very promising
The plan is to have a proposal for the large scale experiment ready by end of 2012