PPC Ge detectors for dark matter, neutrino-less double beta decay and CNS measurements

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1 PPC Ge detectors for dark matter, neutrino-less double beta decay and CNS measurements Ryan Martin, Queen s University Coherent Neutrino Scattering Experiment Workshop, Texas A&M 12 November 2015 R. Martin, Queen's University 1

2 Outline PPC detectors an introduction Coherent neutrino scattering with PPCs Dark Matter Searches with PPCs Neutrinoless double-beta decay with PPCs Slow pulse backgrounds Recent developments using PPC detectors: Segmentation Low noise charge readout Phonon readout R. Martin, Queen's University 2

3 First (n-type) PC detector: P.N. Luke, 1989 First point contact detector Identified as a means to achieve large mass with low energy threshold to search for WIMPs Detector was 800g n-type with depleted capacitance of 1pF FWHM electronic noise = 270eV Electron trapping (n-type crystal) resulted in poor energy resolution at higher energies Pulse shapes show ability to distinguish single and multi-site events R. Martin, Queen's University 3

4 First PPC Collar and Barbeau Motivated to improve on the results of Luke to build a detector for coherent neutrino scattering: Low footprint, good potential for monitoring applications Partnered with CANBERRA Meriden Used ~450g p-type: Better energy resolution (less charge trapping) Thick n+ outer contacts to reduce backgrounds Careful selection of electronics to lower noise Achieved 170eV FWHM electronic noise Showed good charge collection R. Martin, Queen's University 4

5 PPC detectors P-type Point Contact HPGe First one developed by Collar and Barbeau (2008) Small point contact to readout charge, low capacitance, low noise Thick outer contact (n+, lithium diffused), strongly attenuates alphas Large variation in drift times across the detector volume Semi coaxial detector Weighting potential Point contact detector R. Martin, Queen's University 5

6 Properties of PPC detectors PRL (2008) 1332 kev multi-site event in a PPC detector Sharp weighting potential allows multisite events to be identified Gamma rays at 2MeV typically scatter more than once Small capacitance results in low noise and excellent performance at low energies R. Martin, Queen's University 6

7 The CoGeNT neutrino scattering experiment Experiment at San Onofre (SONGS) 30 mwe shielding Very close to seeing the signal! R. Martin, Queen's University 7

8 The CoGeNT dark matter experiment Moved CoGeNT detector underground (Soudan Mine), to characterize backgrounds and to search for dark matter Excess at low energies, time modulation of the excess PRL (2008) PRL (2011) PRD (2013) R. Martin, Queen's University 8

9 CoGeNT future? Some recent developments working with CANBERRA Meriden: Large mass (1.2kg, more??) Significant improvements in low noise readout (~160eV threshold ) PNNL designed an ultra low background cryostat with careful attention to minimizing stray capacitance (98eV FWHM pulser) Dark Matter and/or CENNS? J. Orrell (2013) P. Barbeau (2013) R. Martin, Queen's University 9

10 Dark matter searches with PPCs: MALBEK Almost identical detector to CoGeNT (CANBERRA modified-bege) Deployed by MAJORANA Collaboration at KURF: Develop DAQ for MJD Validate MC Understand backgrounds over a broad energy range DM search No significant excess at low energies Phys Proc (2015) R. Martin, Queen's University 10

11 Dark matter searches with PPCs: TEXONO and CDEX Taiwan and China collaboration TEXONO have a long-standing program to study neutrinos at reactors CDEX China Dark Matter experiment at CJPL (world s deepest lab) CDEX-0 (4 *5g), CDEX-1 (1kg PPC), CDEX-10 (10kg PPCs), CDEX-200 PRD (2014) Complete program to fabricate Ge detectors and electronics by collaboration Funded for 200kg CJPL R. Martin, Queen's University 11

12 0νββ with (germanium) PPC detectors 76 Ge 0νββ Q-value of 2039keV Can be enriched to >87% in 76 Ge (nat. abundance ~ 8%) Good gamma rejection, high purity, 1 channel per detector KKDC 2004 GERDA P EXO CUORE KamLAND-ZEN 2014 Planck 2013 J. Detwiler Probing the inverted hierarchy requires exposures of tonne years for background rates of 1 count per tonne per year in the region of interest! R. Martin, Queen's University 12

13 The MAJORANA DEMONSTRATOR Funded by DOE Office of Nuclear Physics, NSF Particle Astrophysics, NSF Nuclear Physics with additional contributions from international collaborators. Goals: - Demonstrate backgrounds low enough to justify building a tonne scale experiment. - Establish feasibility to construct & field modular arrays of Ge detectors. - Searches for additional physics beyond the standard model. Located underground at 4850 Sanford Underground Research Facility Background Goal in the 0νββ peak region of interest (4 kev at 2039 kev) 3 counts/roi/t/y (after analysis cuts) Assay U.L. currently 3.5 scales to 1 count/roi/t/y for a tonne experiment 44-kg of Ge detectors 29 kg of 87% enriched 76 Ge crystals 15 kg of nat Ge Detector Technology: P-type, point-contact. 2 independent cryostats ultra-clean, electroformed Cu 20 kg of detectors per cryostat naturally scalable Compact Shield low-background passive Cu and Pb shield with active muon veto R. Martin, Queen's University 13

14 Assembled Detector Unit and String Electroformed Copper PTFE PFA + fine Cu coaxial cable Front-End Elec. String Assembly R. Martin, Queen's University 14

15 R. Martin, Queen's University 15 Front-End Board Shipping Restraint Epoxy Feedback Resistor Clean Au+Ti traces on fused silica, amorphous Ge resistor, FET mounted with silver epoxy, EFCu + low-bg Sn contact pin FET Spring Clip

16 The GERDA experiment European search for 0νββ in germanium at LNGS Combination of co-ax and CANBERRA BEGe detectors (14.5kg + 3kg) Bare detectors in LAr Phase 1 results, getting ready for phase 2 T > yr (90%) PRL (2013) R. Martin, Queen's University 16

17 GERDA Phase 2 Additional 20kg of BEGe Instrument LAr active veto Expect to run in Dec 15 TPB coated nylon mini-shrouds R. Martin, Queen's University 17

18 Slow pulse backgrounds in PPCs PRL 106, (2011) CoGeNT first identified slow pulse background Exponentially rising at low energies R. Martin, Queen's University 18

19 Slow pulses in all PPC detectors CDEX, hep-ex v1 MALBEK Seen in CDEX, MALBEK MALBEK had a clear excess from non-ancient Pb shims that held the detector CoGeNT, MALBEK, CDEX apply cuts based on pulse shapes: Difficult to apply pulse shape based cuts on noisy waveforms at low energies R. Martin, Queen's University 19

20 Understanding the transition layer PPC detectors have a lithium diffused outer n+ contact for HV This is not a sharp transition between dead contact and active bulk In the transition layer, diffusion competes with electric field drift and charges can be lost (e.g. recombination), leading to characteristically slow and degraded waveforms At LBNL, we showed that we can measure the fractional energy loss as a function of depth for a detector NIMA 701, 176 (2013) R. Martin, Queen's University 20

21 PPC Detectors: New designs with segmentation for position reconstruction Amman et al. (2009) MPI Munich NIMA 665, 25 (2012) R. Martin, Queen's University 21

22 Recent Developments: CANBERRA ultra low noise detectors CANBERRA France have developed arrays of PPC detectors in low background mounts and cryostats 3x1kg detectors, each with <70eV FWHM pulser noise 3 strings delivered for CDEX-10, to be immersed in LN Leverage industry expertise to design and build low background detector systems R. Martin, Queen's University 22

23 Recent Developments: LBNL ultra low threshold detector Mechanically cooled detector with ASIC CMOS preamp (off the shelf CUBE from XG Labs) Wire-bonded to point contact Record noise level of 39eV at 40K Barton et al., to be published soon R. Martin, Queen's University 23

24 Recent developments: ultra-cold PPCs Simple PPC design used with Luke- Phonon amplification Demonstrated that there is no intrinsic limitation in voltage that can be applied to Ge detectors (e.g. breakdown in CDMSLite) The next frontier is detection of single electron-hole pairs Lowest possible threshold in a Ge detector! Requires a dilution fridge not quite as portable as a device with charge readout! Slow pulses still an issue, need to understand the transition layer if using Li-diffused contact Promising prototype at Berkeley, no breakdown at 400V R. Martin, Queen's University 24

25 Summary Pioneering work by Luke, Collar, Barbeau has led to an intense interest in PPC detector technologies: Dark matter Coherent neutrino scattering Neutrinoless double-beta decay Recent developments: Segmentation for position reconstruction (gamma spectroscopy, background rejections) Ultra low noise performance (CMOS electronics, careful integrated designs) Exploited with Neganov-Luke phonon amplifications Slow pulses from lithium-diffused layer need to be well-understood: Characterize the transition layer New contact technologies (e.g. age) R. Martin, Queen's University 25