Upgrade and progess on the COBRA double beta detector Sudbury, 26. August 2010 Kai Zuber

K. ZuberSudbury, SNOLAB Introduction to COBRA - Current experimental status -Physics results -The pixel option -COBRA Upgrade -Summary

K. ZuberSudbury, SNOLAB 2010 COBRA Use large amount of CdZnTe Semiconductor Detectors K. Zuber, Phys. Lett. B 519,1 (2001) Focus on 116 Cd

K. ZuberSudbury, SNOLAB 2010 Technical University Dresden Technical University Dortmund Laboratori Nazionali del Gran Sasso University of Bratislava Washington University at St. Louis Material Res. Centre Freiburg University of Erlangen-Nürnberg University of Hamburg University of Jyvaskyla University of La Plata Czech Technical University Prague JINR Dubna COBRA collaboration More welcome ? Other institutes: Louisiana State University, University of MIchigan

K. ZuberSudbury, SNOLAB 2010

K. Zuber Isotopes nat. ab. (%)Q (keV)Decay mode

K. ZuberSudbury, 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 116 Cd above MeV Advantages

K. ZuberSudbury, SNOLAB 2010 Beyond MeV background a priori much lower Background S. Pirro, Milano

K. ZuberSudbury, 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 onlyEnergy measurement and tracking Two options

K. ZuberSudbury, SNOLAB 2010 Setup at Gran Sasso Lab

K. ZuberSudbury, SNOLAB 2010 LNGS spectrum

K. ZuberSudbury, 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 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, (2009) six half-life limits above years, one world best, six limits within factor 3 of world best

K. ZuberSudbury, SNOLAB 2010 Coincidence events

K. ZuberSudbury, SNOLAB 2010 The power of coincidences.. Leads to massive background reduction, but at the moment low efficiency Limits obtained not yet competitive with single detector results -> planned upgrade

K. ZuberSudbury, SNOLAB 2010 Background at 2.8 MeV around 5 counts/keV/kg/yr ! Data taking with 16 red crystals finished, about 18 kg*d statistics Major background: Red paint on surface, radon 116 Cd peak region Measured spectrum Actions: Colourless painting (4 + 4 detectors, nitrogen atmosphere with radon trap)

K. ZuberSudbury, SNOLAB 2010 Region of 116 Cd peak Region of interest – Raw data Data cleaning, analysis ongoing

K. ZuberSudbury, 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, SNOLAB 2010 Pixel size ( 130 Te) Reasonable range For 200  m 130 Te and 116 Cd would hit about 7-10 pixel

K. Zuber 20x20x5 mm 3 systems 8x8 pixels (running at LNGS Jan. –May 2010) 32x32 pixel system 100x100 pixel system Timepix system: 14x14x0.3 mm 3 Si ( 2 systems) 14x14x1 mm 3 CdTe (2 systems) 256x256 systems 128x128 systems World largest CZT detector = 36 grams collaboration with Zhong He (Univ. of Michigan) 20x20x15 mm 3 11x11 pixel system Up to 40 slices in z by pulse information Running at LNGS from Sep Jan One system running in Felsenkeller Lab since Sep. 2009, one running at LNGS since May 2010, before Modane COBRA – Pixel CZT Sudbury, 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 z up to 40 slices due to drift time Polaris system (U Mich)

K. Zuber Polaris system The power of pixels! Together with University of Michigan (group Zhong He) Sudbury, SNOLAB 2010 Running at LNGS from Sep Jan. 2010

K. Zuber No survivor after 125 days of data taking!!! Corresponds to a background between keV of 0.9 counts/keV/kg/yr Detector not tuned for low background Polaris system 116Cd peak region Sudbury, SNOLAB 2010

K. Zuber Timepix It reacts on environment, ie. not completely dominated by internal background 55 μm pixel Si Timepix device

K. Zuber A nice muon... A nice muon

K. ZuberSudbury, SNOLAB 2010 Timepix Electrons Particle identification as background reduction tool works! 256x256 pixels, 55  m MuonsAlphas

K. ZuberSudbury, SNOLAB 2010 Picture show NO event in days in energy range between 2.7 and 3 MeV which looks like 1(2) electrons

K. ZuberSudbury, SNOLAB 2010 Idea: Massive background reduction by particle identification 200 μm pixel simulation Bi-214 = Time coincidence of both alphaelectron 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. Bush Yes we can! B. Obama

K. ZuberSudbury, SNOLAB 2010 COBRA Upgrade 2010/11 Upgrade to 64 CZT 1 cm 3 detectors, about 0.42 kg (all detectors at hand) Single grid readout, i.e. pulse shaping Improved shielding, readout (new DAQ), material selection Active veto (CsI), strongly enhances physics potential Aim : Background below 1 count/keV/kg/yr Running CZT in LSci Produce enriched CZT detectors Running a larger scale Polaris system and pixel systems

K. ZuberSudbury, SNOLAB 2010 Pulse shape Much more information in pulse shape CPG detector works like a Frisch grid in wire chambers P. Luke, IEEE Trans. NS 42, 207 (1995) 60 Co pulse Experiment TCAD simulation Single site eventMultiple site event J. McGrath et al., NIM A 615,57 (2010) Modification of preamps necessary... Done First new preamps and two FADCs installed at LNGS this week

K. ZuberSudbury, SNOLAB 2010 COBRA Upgrade Aim : Improve excited state and positron decay sensitivity by factor Done for : NaI, CsI, BGO, CdWO 4 Exploring various readout concepts Note: Can tolerate some impurities because of coincidence requirement 128 Te 1st excited state 116 Cd 1st excited state

K. ZuberSudbury, SNOLAB 2010 Material screening (DLB) Factor of 1000 reduction with respect to unshielded

K. ZuberSudbury, 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, SNOLAB 2010

K. ZuberSudbury, SNOLAB 2010 King Cobra Measurement of 50 meV neutrino mass would require about 400 kg of CZT, isotopically enriched in Cd-116 Shielding must be able to reduce background to less than events /kg/keV/yr Plan is to have TDR by end of 2012

K. ZuberCambridge, 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 next year  Unique 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