ppc ge detectors for dark matter, neutrino-less double...

PPC Ge detectors for dark matter, neutrino-less double beta decay and CNS measurementsRyan Martin, Queen’s UniversityCoherent Neutrino Scattering Experiment Workshop, Texas A&M12 November 2015

R. Martin, Queen's University 1

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


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

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

• 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

Point contact detector

Weightingpotential

PPC detectors


• Sharp weighting potential allows multi-site 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

1332 keVmulti-site event in a PPC detector

PRL 101 251301 (2008)

Properties of PPC detectors


The CoGeNT neutrino scattering experiment


• Experiment at San Onofre(SONGS)

• 30 mwe shielding• Very close to seeing the

signal!

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 101 251301 (2008) PRL 106 131301 (2011)

PRD 88 012022 (2013)

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?

P. Barbeau (2013)

J. Orrell (2013)

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 61 77 (2015)

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 90 032003 (2014)

• Complete program to fabricate Ge detectors and electronics by collaboration

• Funded for 200kg phase @ CJPL

0νββ with (germanium) PPC detectors


Probing the inverted hierarchy requires exposures of tonne years for background rates of 1 count per tonne per year in the region of interest!

• 76Ge 0νββ Q-value of 2039keV • Can be enriched to >87% in 76Ge (nat. abundance ~ 8%)• Good gamma rejection, high purity, 1 channel per detector

CUORE-0 2015GERDA P1 2013 EXO-200 2014

KamLAND-ZEN 2014

KKDC 2004

Planck 2013 J. Detwiler

• 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 ≤ 3.5scales to 1 count/ROI/t/y for a tonne experiment

• 44-kg of Ge detectors– 29 kg of 87% enriched 76Ge crystals– 15 kg of natGe– 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

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.

13R. Martin, Queen's University

Assembled Detector Unit and String

14

ElectroformedCopper

PTFE

PFA + fine Cucoaxial cable

String Assembly

Front-End Elec.

R. Martin, Queen's University

Front-End Board

15

Epoxy

ShippingRestraint Feedback Resistor

FET Spring Clip

Clean Au+Ti traces on fused silica, amorphous Ge resistor, FET mounted with silver epoxy, EFCu + low-BG Sn contact pin

R. Martin, Queen's University

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

PRL 111 122503 (2013)T > 2.1 1025 yr (90%)

GERDA Phase 2


• Additional 20kg of BEGe• Instrument LAr active veto• Expect to run in Dec ‘15

TPB coated nylon mini-shrouds

Slow pulse backgrounds in PPCs


PRL 106, 131301 (2011)

• CoGeNT first identified “slow pulse background”

• Exponentially rising at low energies

Slow pulses in all PPC detectors


CDEX, hep-ex 1404.4946v1

• 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

MALBEK

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)

PPC Detectors: New designs with segmentation for position reconstruction


NIMA 665, 25 (2012) Amman et al. (2009) MPI Munich

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

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

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

Summary


• Pioneering work by Luke, Collar, Barbeauhas 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)

ppc ge detectors for dark matter, neutrino-less double...

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