Recent Progress on D 3 - The Directional Dark Matter Detector Sven E. Vahsen, University of Hawaii...

Sven Vahsen (U. Hawaii)

Recent Progress on D3 - The Directional Dark Matter Detector

Sven E. Vahsen, University of HawaiiCYGNUS 2015 1

alpha particle track detected with latest detector prototype

• Detection Principle• Motivation• Prototypes constructed• Their performance• Next steps

D3 - Directional Dark Matter Detector

CYGNUS 2015 Sven Vahsen (U. Hawaii) 2

Berkeley Lab HawaiiLBNL Hawaii

• 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

D3 - micro

Team at U. Hawaii and Berkeley Lab

John Kadyk Maurice Garcia-Sciveres

Kelsey Oliver-Mallory(UC Berkeley Student)

Sven E. Vahsen

Michael HedgesGraduate Student

Ilsoo SeongGraduate Student

Thomas ThorpeGraduate Student


Mayra Lopez-Thibodeaux(UC Berkeley Student)

Kamaluoawaiku BeamerUndergraduate Student(+rotating group)

Peter LewisPostdoc

Josh MurilloGraduate Student

• charge amplification w/ CERN GEMs

• charge Detection with ATLAS pixel chips

• custom metallization• perhaps electrostatic

charge focusing

Detector Concept

CYGNUS 2015 Sven Vahsen (U. Hawaii) 4CYGNUS 2015 Sven Vahsen (U. Hawaii) 4

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

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-

Gas Electron Multiplier (GEM)

Pixel Electronics

50 μm

• ATLAS FE-I3• 50x400 μm pixels • Sampling at 40 MHz

+ =

Cosmic ray track (~7mm)

size of each bubble showsamount of ionization measured

Note absence of noise hits

~2keV

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

http://arxiv.org/abs/1110.3401

D3 P

relim

inar

y

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!

D3 Micro: 1 cm3 (2011)

• 1 cm3


ATLAS FE-I350 x 400 µm pixels 7.4 by 11.0 mm

active

Pixel chip:

cathode

GEM foil

circuit board that holds pixel chip

D3 Micro: Example of Events

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!

ArCO2 (70:30)p=1 atm

HeCO2 (70:30)p=1 atm

E~ 2 keV E~ 1 keV

What limits the Readout Plane Resolution?

Colloquium @ UH Manoa Sven Vahsen 9

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.

Angular resolution versus “track size”


Angular resolution can be predicted analytically from point resolution. Agrees well with measurement. Allows extrapolation to other energies and gas pressures

I. Seong

Alpha particles

Analytical “prediction”:

What Limits The Energy Resolution?


• 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

ArC02 at p=1atm

Limited by gas ionization& avalanche processes

Limited byanalog PHA electronics

PHA

T. Thorpe

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 12

D3 Micro-5: ~2.5 cm3 (2013)



active

Pixel chip:

Cf-252 Source Present

Source Absent

D3 Micro-5: 3D Directional Neutron Detection

27-sigma evidence for “neutron wind” in our lab! Recoils point back to source, in 3D.

He-recoil measured in HeC02 gas at p=1atm L ~ 5 mm E ~ 350 keV/c2

Incoming neutronScattered neutron

Nucle

ar re

coil

neutron source

Mean direction of nuclear recoils corresponds to neutron source location

D3 Micro-20: 20 cm3 (2013)


CYGNUS 2015 Sven Vahsen (U. Hawaii)

~60 cm3 TPC w/ Field Cage (2014)

Latest


active

Pixel chip:

16

Prototype fast neutron detector.Small footprint enabled byParylene coating on inside of pressure vessel


Final Micro-TPC Prototype Design

Sensitive volume

Charge amplification(GEMs)

Field cage

Charge Detection(Pixel Chip)Aluminum vacuum vessel


Micro-TPC Assembly and Testing in Hawaii Clean Room


Micro-TPC Prototype: First Events• Figures show 2-D projection

of charge measured w/ pixel chip– – 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)

– particle

– reco

il

neut

ron

char

ge

char

ge

Final prototype exceedsperformance objectives.Uniformity issue also solved.

no noise hits!


Internal Calibration Sources• Three Po-210 alpha-particle sources

source 1source 2source 3

in-situ, time-dependent , and z-dependent calibration of energy scale and detailed response to helium recoils


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 time (one week total)

ioni

zatio

n m

easu

red

source 1

source 2

source 3

Sufficient stability to observe annual oscillation in WIMP rate / spectrum


Angular and Energy Resolution – 2cm alpha tracks

• Sub-1-degree angular resolution even after ~15 cm drift. • Energy resolution now comparable to gain resolution.


I. Seong I. Seong


nHe

Ionization cloud from ~1MeV recoiling He-nucleus, measured in 3D

High Energy Nuclear Recoil in 3D

• each block:50x250x250 μm3

• Color: ionizationdensity

Medium Energy Nuclear Recoil in 3D


• each block:50x250x250 μm3

• Color: ionizationdensity

Ionization cloud from Eee~25 keV recoiling He-nucleus, measured in 3D

Absolute Position Measurement

• Measurement of charge-profile (not width) of track, enables accurate measurement of transverse diffusion

obtain absolute position in drift direction

P.Lewis


Absolute Position Measurement

December 18, 2014 US Belle II Project Mini Review 26

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)

P.Lewis

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 %

Without source present

With source present


I. Seong

Cf-252 data, recoil ionization energy spectrum, before position cut

With source present

Without source present

Detector is essentially background free for high-energy neutron recoil events.

From cathode mesh. Rejected by position cut


I. Seong

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


D-D neutron generator test at LBNL


LBNL test: Observed Neutron Signal

• Measured neutron rate follows generated neutron rate• Max generated rate is 2x107 neutrons / second, approx. isotropic

I. Seong


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


Existing and Next Generation Detectors

µD3 (1cm3 )

2011

2015 - 2016

planned

mD3 (~10 liters)

D3 (~1m3 )

Ingredients1. ATLAS FE-I4 pixel chips 2. thick GEMs3. existing ATLAS DAQ 4. negative ion drift (potentially multiple benefits:

reduced diffusion, track tomography, electron counting)

5. electrostatic focusing of drift charge

1 pixel chip 4 pixel chips

~400 pixel chipsCYGNUS 2015 Sven Vahsen (U. Hawaii) 33

20132014

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 technologyalso of interest for precision studiesof nuclear recoils


Recent Progress on D 3 - The Directional Dark Matter Detector Sven E. Vahsen, University of Hawaii...

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