1. Recent Progress on D3 - The Directional Dark Matter Detector
Detection Principle
Motivation
Prototypes constructed
Their performance
Next steps
alpha particle track detected with latest detector prototype
Sven E. Vahsen, University of Hawaii
CYGNUS 2015
Sven Vahsen (U. Hawaii)

2. D3 - Directional Dark Matter Detector
Investigating feasibility of directional DM search w/ micro-pattern gas detectors
Technology also of interest for detecting neutrons and charged particles
Small (1-60 cm3) prototypes built at LBNL and U. Hawaii
Ongoing since ~Fall 2010
Berkeley Lab
Hawaii
LBNL Hawaii
D3 - micro
CYGNUS 2015
Sven Vahsen (U. Hawaii)

3. Team at U. Hawaii and Berkeley Lab
Peter Lewis
Postdoc
John Kadyk
Maurice Garcia-Sciveres
Kelsey Oliver-Mallory
(UC Berkeley Student)
Michael Hedges
Graduate Student
Josh Murillo
Graduate Student
Thomas Thorpe
Graduate Student
Mayra Lopez-Thibodeaux (UC Berkeley Student)
Ilsoo Seong
Graduate Student
Kamaluoawaiku Beamer
Undergraduate Student
(+rotating group)
Sven E. Vahsen
CYGNUS 2015
Sven Vahsen (U. Hawaii)

4. Detector Concept charge amplification w/ CERN GEMs
charge Detection with ATLAS pixel chips
custom metallization
perhaps electrostatic charge focusing
CYGNUS 2015
CYGNUS 2015
Sven Vahsen (U. Hawaii)
Sven Vahsen (U. Hawaii) 4

5. Charge Amplification and Detection in D3
Drift charge amplified with double layer of GEMs - gain ~20k at 1 atm
Detected with pixel electronics - threshold ~2k e-, noise ~ 100 e-
Cosmic ray track (~7mm)
Gas Electron Multiplier (GEM)
Pixel Electronics
50 μm
ATLAS FE-I3
50x400 μm pixels
Sampling at 40 MHz
~2keV + =
Note absence
of noise hits
size of each bubble shows
amount of ionization measured
Advantages of this approach
Full 3D tracking w/ ionization measurement for each space-point (head/tail sensitivity)  improved WIMP sensitivity and rejection of alpha particle backgrounds
Pixels ultra-low noise (~100 electrons), self-triggering, and zero suppressed  virtually noise free at room temperature  low demands on DAQ
High-single electron efficiency  suitable for low-mass WIMP search
New: pixel-level charge measurement enables
3D fiducialization  improved background rejection
Estimate of non-detected charge  improved energy resolution + BG rejection

6. The Case for Low Track Energy Threshold
Preliminary evaluation: 3-m3 detector could achieve directional sensitivity to (controversial) ~10 GeV WIMPS
Golden scenario - if DAMA/LIBRA were due to WIMPs:
observe ~1000s of non-directional events (can observe yearly oscillation)
use subset (~100) of these to search for daily directional oscillation, to determine if BG or WIMPs
D3 Preliminary
Estimated sensitivity to spin-independent WIMP-nucleon scattering, 3-m3 directional dark matter detector, running for 3 years with 33 cm drift length and CF4 gas, for four different track reconstruction thresholds and for non-directional analysis.
Superior S/N & track energy treshold of order 10 keV crucial for detecting 10 GeV WIMPS!
CYGNUS 2015
Sven Vahsen (U. Hawaii)

7. D3 Micro: 1 cm3 (2011) 1 cm3 cathode GEM foil circuit board that
Pixel chip:
active
ATLAS FE-I3
50 x 400 µm pixels
7.4 by 11.0 mm
circuit board that
holds pixel chip
CYGNUS 2015
Sven Vahsen (U. Hawaii)

8. D3 Micro: Example of Events
ArCO2 (70:30)
p=1 atm
HeCO2 (70:30)
p=1 atm
E~ 2 keV
E~ 1 keV
Cosmic ray events to demonstrate tracking w/ low track-energy threshold
each block: 50x400x400 μm3. Color shows measured ionization density
hit threshold ~ 30eV. Note absence of noise hits!

9. What limits the Readout Plane Resolution?
Point resolution for short pixel dimension not limited by detector segmentation, but by diffusion internal to the readout plane. Don’t need much smaller pixels.
UH Manoa
Sven Vahsen

10. Angular resolution versus “track size”
I. Seong
Analytical “prediction”:
Alpha particles
Angular resolution can be predicted analytically from point resolution. Agrees well with measurement. Allows extrapolation to other energies and gas pressures
UH Manoa
Sven Vahsen

11. What Limits The Energy Resolution?
Limited by gas ionization
& avalanche processes
Limited by
analog PHA electronics
ArC02 at p=1atm
T. Thorpe
PHA
Good gain resolution for MeV-scale signals, adequate even for few-keV signals!
Expect to achieve good head-tail identification, perhaps even in keV range
UH Manoa
Sven Vahsen

12. Energy Resolution – Initial Problems
In this first prototype, the energy resolution observed with the pixel chip was however much worse than gain resolution
Due to defects in the metallization layer
Now resolved
July 2013 Sven Vahsen
ARI Grantees Conference

13. D3 Micro-5: ~2.5 cm3 (2013) Pixel chip: active ATLAS FE-I3
50 x 400 µm pixels
7.4 by 11.0 mm
CYGNUS 2015
Sven Vahsen (U. Hawaii)

14. D3 Micro-5: 3D Directional Neutron Detection
Source Absent
He-recoil measured in HeC02 gas at p=1atm
L ~ 5 mm
E ~ 350 keV/c2
Mean direction of nuclear recoils corresponds to neutron source location
Nuclear recoil
Cf-252 Source Present
Incoming neutron
Scattered neutron
neutron
source
27-sigma evidence for “neutron wind” in our lab! Recoils point back to source, in 3D.

15. D3 Micro-20: 20 cm3 (2013)
CYGNUS 2015
Sven Vahsen (U. Hawaii)

16. ~60 cm3 TPC w/ Field Cage (2014) Pixel chip: active
ATLAS FE-I4
50 x 250 µm pixels
20.3 by 19.2 mm
Prototype fast neutron detector.
Small footprint enabled by
Parylene coating on inside of pressure vessel
Latest
CYGNUS 2015
Sven Vahsen (U. Hawaii)
CYGNUS 2015
Sven Vahsen (U. Hawaii) 16

17. Final Micro-TPC Prototype Design
Sensitive volume
Field cage
Charge amplification (GEMs)
Charge Detection
(Pixel Chip)
Aluminum vacuum vessel
CYGNUS 2015
Sven Vahsen (U. Hawaii) 17

18. Micro-TPC Assembly and Testing in Hawaii Clean Room
CYGNUS 2015
Sven Vahsen (U. Hawaii) 18

19. Micro-TPC Prototype: First Events
Figures show 2-D projection of charge measured w/ pixel chip
𝛼 – particle event: Po-210 source inside vacuum vessel at z=15 cm, i.e. charge has drifted through entire detector
Neutron recoil event: Cf-252 source outside vacuum vessel, pointed at z=8 cm (middle of TPC)
𝛼 – particle
charge
no noise hits!
neutron
𝐻𝑒 – recoil
charge
Final prototype exceeds
performance objectives.
Uniformity issue also solved.
CYGNUS 2015
Sven Vahsen (U. Hawaii) 19

20. Internal Calibration Sources
Three Po-210 alpha-particle sources
source 3
source 2
source 1
in-situ, time-dependent , and z-dependent calibration of energy scale and detailed response to helium recoils
CYGNUS 2015
Sven Vahsen (U. Hawaii) 20

21. Long Term Stability Test
Continuous operation and DAQ for >1 month, summer 2014
Flow-rate controller and pressure regulator
Excellent gain stability, at ~1% level per week, pre-calibration, during stable lab conditions, as shown on right
Can be calibrated out with the calibration source data
source 1
source 2
ionization measured
source 3
time (one week total)
Sufficient stability to observe annual oscillation in WIMP rate / spectrum
CYGNUS 2015
Sven Vahsen (U. Hawaii) 21

22. Angular and Energy Resolution – 2cm alpha tracks
I. Seong
I. Seong
Sub-1-degree angular resolution even after ~15 cm drift.
Energy resolution now comparable to gain resolution.
CYGNUS 2015
Sven Vahsen (U. Hawaii) 22

23. High Energy Nuclear Recoil in 3D
each block: 50x250x250 μm3
Color: ionization density He n
Ionization cloud from ~1MeV recoiling He-nucleus, measured in 3D
CYGNUS 2015
Sven Vahsen (U. Hawaii)

24. Medium Energy Nuclear Recoil in 3D
each block: 50x250x250 μm3
Color: ionization density
Ionization cloud from Eee~25 keV recoiling He-nucleus, measured in 3D
CYGNUS 2015
Sven Vahsen (U. Hawaii)

25. Absolute Position Measurement
P.Lewis
Measurement of charge-profile (not width) of track, enables accurate measurement of transverse diffusion
 obtain absolute position in drift direction
CYGNUS 2015
Sven Vahsen (U. Hawaii) 25

26. Absolute Position Measurement
P.Lewis
2-mm track segments.
8-mm track segments.
 enables 3D-fiducialization, even for very short track, presumably for more or less any gas
Charge profile analysis also enables “Energy Recovery” (unpublished)
December 18, 2014
US Belle II Project Mini Review

27. Fast Neutron Detection (preliminary, unpublished)
Extended absolute position measurement to neutron recoil events
Neutron detection w/ Cf-252 source at U. Hawaii
1 background event from internal radioactivity per week, 2x105 lower than assumed in design simulations!
Neutron Signal Selection efficiency, estimated w/ GEANT4: ~40 %
With source present
Without source present
I. Seong
CYGNUS 2015
Sven Vahsen (U. Hawaii) 27

28. Cf-252 data, recoil ionization energy spectrum, before position cut
With source present
I. Seong
Without source present
From cathode mesh. Rejected by position cut
Detector is essentially background free for high-energy neutron recoil events.
CYGNUS 2015
Sven Vahsen (U. Hawaii) 28

29. D-D neutron generator test at LBNL
Deployed from Hawaii to California
Neutrons observed, but not easily
Surprises: huge x-ray background, E&M interference, and GND line fluctuations
CYGNUS 2015
Sven Vahsen (U. Hawaii) 29

30. D-D neutron generator test at LBNL
CYGNUS 2015
Sven Vahsen (U. Hawaii) 30

31. LBNL test: Observed Neutron Signal
I. Seong
Measured neutron rate follows generated neutron rate
Max generated rate is 2x107 neutrons / second, approx. isotropic
CYGNUS 2015
Sven Vahsen (U. Hawaii) 31

32. LBNL test: observed neutron signal
Measured energy spectrum in reasonable agreement with simulation
Note: Plot shows observed ionization energy of recoils.
Further analysis needed to obtain neutron energy distribution. Must correct for detection losses & scattering angle
Rich analysis – in progress
I. Seong
CYGNUS 2015
Sven Vahsen (U. Hawaii) 32

33. Existing and Next Generation Detectors
2011
2014
2013
µD3 (1cm3 )
mD3 (~10 liters)
1 pixel chip
4 pixel chips
Ingredients
ATLAS FE-I4 pixel chips
thick GEMs
existing ATLAS DAQ
negative ion drift (potentially multiple benefits: reduced diffusion, track tomography, electron counting)
electrostatic focusing of drift charge
planned
D3 (~1m3 )
~400 pixel chips
CYGNUS 2015
Sven Vahsen (U. Hawaii)

34. Conclusion
m3-scale gas TPC w/ low energy threshold may be sufficient to investigate hints for low-mass WIMPs w/ directionality
Will require superior S/N and 10 keV track energy threshold
A TPC with charge readout via GEMS and Pixel might have the required performance characteristics
A series of prototypes have been built
Performance measured and limiting factors understood from the ground up
Excellent S/N, spatial resolution, and energy resolution
The apparently excessive spatial resolution enables new BG reduction techniques
Detectors based on this technology also of interest for precision studies of nuclear recoils
CYGNUS 2015
Sven Vahsen (U. Hawaii)