1. Searching for Dark Matter with the CoGeNT and C4 Detectors
Mark Kos, PNNL
PNNL-SA-92945

2. Overview Status of CoGeNT
Latest results
Current understanding of backgrounds
Steps to help reduce/eliminate the major backgrounds we see in CoGeNT
Simulation of the C4 backgrounds
Expected WIMP (Weakly Interacting Massive Particle) sensitivity of C4
Implications for future low-mass dark matter searches

3. CoGeNT results and low-mass WIMPs
Published CoGeNT analysis shows an excess of events at low energies that is inconsistent with known backgrounds, but hint at low mass WIMPs (Weakly Interacting Massive Particles)
Also, a hint of annual modulation consistent with WIMP dark matter
The CoGeNT results have sparked an interest in low-mass WIMPs
Need multiple detectors with lower backgrounds and lower thresholds to test the CoGeNT results: C-4
Phys. Rev. Lett. 107 (2011)
arXiv:

4. CoGeNT shield design
CoGeNT: 1 Ge crystal (440 g) at the Soudan mine (data taking since Dec 2009)

5. The background picture
68Ge
arXiv:
Background sum
65Zn
L-shell contribution
68Ga
Resistor gammas ~324 events, ~16% of data
49V
54Mn
55Fe
56,57,58Co
51Cr
73,74As
Tritium b-decay 150 events, 7% of data
Muon-induced neutrons 339 events, 16% of data
Cavern neutrons (from radioactivity) 54 events, 3% of data
Other sources of background simulated:
U and Th chain backgrounds in surrounding material (copper)
Muon-induced neutrons from the cavern
U and Th chain backgrounds in lead shielding
Spontaneous fission neutrons from shielding material
(a,n) neutrons from shielding material
These backgrounds are tiny

6. Muon-induced neutrons (largest background)
4/14/2017
Muon-induced neutrons (largest background)
1 cm panels do not allow muon-gamma separation
Veto operated at single photo-electron sensitivity
Generate ~12% dead time from spurious germanium detector-veto coincidences.
True coincidences are however observable and rate is in good agreement with Monte-carlo (next slide)
PNNL is a partner in education, research, and economic development.
Across Washington, both Battelle and PNNL have invested in science education in our primary and secondary schools, and we continue to host students, high-school level and above, via educational appointments.
We partner with universities and colleges to strengthen our research base and provide opportunities for the up and coming workforce:
University of Washington -- Joint institute for nano-science and technology
University of Maryland – Joint Global Climate Change Research
State of Oregon – Microproducts Breakthrough Institute
The intellectual property developed at PNNL can be designated for use in local and regional partnerships that enhance economic development:
Creates new business starts
Helps existing businesses grow through new and improved products or product lines
Attracts outside businesses into the area
These goals can only be accomplished through teamwork with local and regional economic development agencies, including the Tri-City Industrial Development Council (TRIDEC), Columbia Basin College, Washington State University, PNNL, site contractors, and other entities.
Over the past 13 years, PNNL’s economic development programs have added more than 1,100 jobs and millions of dollars to the economic base of the region. We have provided nearly 800 technology assistance projects to more than 500 technology businesses nationwide since EDO has pressed on with singular focus on our goals: to expand the economy's technology sector and create high-value jobs.
Updated October 2010 | PNNL-SA-70564

7. Muon-induced neutron simulation
4/14/2017 m-
Two independent MC simulations used to
assess neutron contributions
muon induced neutron
natural radioactivity in cavern
#1: GEANT
Soudan muon flux, E, angular distribution
to generate (m,n) in full shield.
Includes e- and g (8% of neutron contribution)
#2 MCNP-Polimi:
Neutron generation in lead shielding (largest contributor)
Reasonable agreement between simulations (they use different inputs) 339 +/- 68 events (GEANT)
GEANT
CoGeNT data
PNNL is a partner in education, research, and economic development.
Across Washington, both Battelle and PNNL have invested in science education in our primary and secondary schools, and we continue to host students, high-school level and above, via educational appointments.
We partner with universities and colleges to strengthen our research base and provide opportunities for the up and coming workforce:
University of Washington -- Joint institute for nano-science and technology
University of Maryland – Joint Global Climate Change Research
State of Oregon – Microproducts Breakthrough Institute
The intellectual property developed at PNNL can be designated for use in local and regional partnerships that enhance economic development:
Creates new business starts
Helps existing businesses grow through new and improved products or product lines
Attracts outside businesses into the area
These goals can only be accomplished through teamwork with local and regional economic development agencies, including the Tri-City Industrial Development Council (TRIDEC), Columbia Basin College, Washington State University, PNNL, site contractors, and other entities.
Over the past 13 years, PNNL’s economic development programs have added more than 1,100 jobs and millions of dollars to the economic base of the region. We have provided nearly 800 technology assistance projects to more than 500 technology businesses nationwide since EDO has pressed on with singular focus on our goals: to expand the economy's technology sector and create high-value jobs.
MCNP-Polimi
Mostly neutrons, ~8% e- and g’s
(simulation)
Less than 16% neutron fraction in CoGeNT data after L-shell subtractions
Updated October 2010 | PNNL-SA-70564

8. Backgrounds from the front end electronics (2nd largest background)
RESISTORS ARE HOT!
Description
U-238
(Bq/kg)
Th-232
K-40
Events in CoGeNT
Carbon film resistor
4.3
12.7
21.9
972 +/- 120
Metal film resistor 1
0.5
37.5
324 +/- 164
Metal film resistor 2
5.1
16.1
24.7
1208 +/- 160
Ceramic core resistor
5.9
4.6
34.3
644 +/- 131
Metal on ceramic resistor 28
40.7
25.7
4509 +/- 352
Ceramic
15.5
0.2
13.8
993 +/- 200
ILIAS database
SNOLAB

9. Most beta-spectra and gammas are a flat background in the CoGeNT analysis region
This is expected from Compton scattering of high energy photons at these low energies
A background that can be reduced by having tightly packed detectors and rejecting multiples
Without an assay we cannot be sure the flat background is from the resistors, but typical resistor backgrounds can plausibly explain most of the CoGeNT flat background

10. Tritium production in germanium (3rd largest background)
4/14/2017
Tritium production in germanium (3rd largest background)
Years of surface exposure
Tritium decays underground 1
299 2
583 3
850 4
1103 5
1342 6
1568 7
1782 8
1983 9
2174 10
2355
Cosmogenic production of tritium in Ge while detector at surface
Tritium b-decay endpoint at 18.6 keV
Half-life of yrs
Tritium production rate:
27.7 /kg-day Astroparticle phys, 31, 417 (2009)
Based on IGEX data Phys Lett, B432, 8 (2002)
Assuming a surface exposure of CoGeNT detector of 2 yrs:
150 events in 0.5 – 3.0 keVee (Geant4 simulation of 3H in CoGeNT)
CoGeNT Data
The science and technology research we conduct wouldn’t be possible without key facilities.
Pictured here is our main campus, which includes EMSL (featured on next slide), the Computational and Biological Sciences Facilities (opened in Fall 2009), and the Physical Sciences Facility complex (opening in Fall 2010).
Other key facilities:
The Bioproducts, Sciences, & Engineering Laboratory is a multipurpose research and development facility that includes operating space for all activities required to advance the science and engineering of processes for bio-based product manufacture. The building is located on the campus of Washington State University (WSU) Tri-Cities, approximately one mile south of the main campus of PNNL.
The Radiochemistry Processing Laboratory at PNNL is one of a few category II nuclear R&D facilities in the DOE complex. The facility’s mission has changed along with national priorities. It first supported the Hanford site during plutonium production days, and since then it’s been used for separating and processing waste, and developing immobilization technologies. Ownership of the facility transferred from EM to the Office of Science, and it’s is now recognized as a critical component of energy and national security research. We’re making infrastructure improvements to it that will extend its life another 20 years.
The Atmospheric Radiation Measurement mobile facility is a comprehensive set of world-class, and in some cases, unique, instruments that are available for use by the global scientific community. Key instruments include one of the few operational Raman Lidar in the world; millimeter wavelength cloud radar; radar wind profilers; and total sky imagers. More recent additions to the suite of ARM instrumentation are the microwave radiometer and the advanced rotating shadowband spectrometer.
The Electricity Infrastructure Operations Center brings together industry software, real-time grid data, and advanced computation into a functional control room. This unique integrated energy operations capability was shaped with input from utilities and researchers across the Northwest.
The Environmental Molecular Sciences Facility is a DOE national scientific user facility (featured on next slide).
Tritium (simulation)
Updated October 2010 | PNNL-SA-70564 10

11. Neutrons from radioactivity in the cavern: (a,n) + fission
4/14/2017
Use Mei-Hime neutron flux:
3.78 X 10-6 cm-2 s-1 (Phys Rev D 73 , (2006))
Use Monte-carlo neutron energy spectrum from Gran Sasso (worst case)
Simulated background for CoGeNT:
54 events in the dataset
Awards:
R&D 100 Awards – “The Oscars of Invention” (The Chicago Tribune)
The winning of an R&D 100 Award provides a mark of excellence known to industry, government, and academia as proof that the product is one of the most innovative ideas of the year. PNNL has earned 80 R&D 100 Awards, ranging from scientific instruments and novel materials to information analysis systems that help ensure the nation’s security and provide a competitive advantage to industry.
2009 R&D Awards included:
1) PowerPuck™ helps create electrical energy from the environment. Electricity can be created by processing heat associated with naturally occurring temperature differences in the environment. This essentially inexhaustible source of heat can be converted into electrical power sufficient to run compact, low-power devices like wireless sensors. PNNL’s commercial partner, Perpetua, shares this R&D 100 honor with us. Team members included John DeSteese, Larry Olsen (PNNL); Paul McClelland, Jon Hofmeister (Perpetua Power Source Technologies). [TOP PICTURE]
2) Ultrasensitive ESI-MS Source & Interface is improved electrospray ionization-mass spectrometry (ESI-MS) instrumentation that provides precise measurements of compounds in a sample, even when little material is available. The technology also provides a 40-fold increase in sensitivity, benefiting applications in human health, the environment, and pharmaceutical and petrochemical industries[BOTTOM PICTURE]
FLC Awards –Federal Laboratory Consortium (FLC) Awards for Excellence in Technology Transfer. PNNL has received 69 Laboratory Consortium awards for Excellence in Technology Transfer—by far the most of any DOE national laboratory.
Christopher Columbus Awards – Our scientists have won the prestigious Christopher Columbus Award for “scientific inventions that will change our lives.” Each year, the Christopher Columbus Foundation honors a scientist who is trying to improve the world through scientific endeavors and chooses the recipient from entries to the annual Discover Magazine Innovation Awards. [Jim Thomas (2009) in Homeland Security for his work in creating computerized visual analytics technology that can be used to predict and prevent acts of terrorism or other catastrophic events. Doug McMakin and team (2007) in Homeland Security; developed and tested innovative real-time microwave and millimeter-wave holographic-imaging systems for airport personnel screening. Aaron Diaz (2004) for research focused on ultrasonic nondestructive examination measurements, imaging, and analysis. This work has resulted in the development of the Acoustic Inspection Device, a state-of-the-art technology used by U.S. and international Customs Officers and other law enforcement officials for counterterrorism and drug interdiction activities. Dr. Richard Craig (2001) for the development of the Timed Neutron Detection (TND) of Land Mines. This device finds plastic and metal mines by locating the hydrogen atoms that make up the destructive war devices. ]
Other Distinguishing Honors:
Numerous scientific and engineering society fellowships, awards, and elected committee positions.
Noble cause for a Nobel Prize - More than 20 scientists from the Laboratory contributed to the global efforts of the Intergovernmental Panel on Climate Change, which received the 2007 Nobel Peace Prize in equal part with former Vice President Al Gore. PNNL scientists contributed to the authoritative assessments of climate change, its impacts, and the set of technological, institutional, and policy options available to mitigate and adapt to global change.
Patents – 1,778 patents issued to PNNL since 1965 (report generated October 2009 and includes 979 U.S. and 799 foreign patents). In 2008, there were 42 U.S. and 49 foreign for a total of 91 that calendar year.
Deep underground this background is higher than muon-induced neutrons
Something that experiments pushing the zero-background limit need to address
Updated October 2010 | PNNL-SA-70564

12. Radioactivity in the CoGeNT shield
SNOLAB assay of similar materials as used in CoGeNT
Material
238U (mBq/kg)
232Th (mBq/kg)
210Po (Bq/kg)
Lead sample1
0.41 +/- 0.17
0.08+/-0.08
93 +/- 19
Plastic lumber
121 +/- 4
68 +/- 3
(recycled)
115 +/- 5
80 +/- 4
Plastic lumber McMaster-Carr
15 +/- 1
1.3 +/- 0.8
Aluminum plate
7.1 +/- 2.4
986 +/- 12
Aluminum framing pieces
42 +/- 8
1348 +/- 50
210Pb  210Bi  210Po  206Pb
Ultra-low background lead around CoGeNT: Bq/kg 210Pb
Source of (a,n) neutrons

13. List of all backgrounds (we know about)
Source
Events in CoGeNT dataset
(0.5 – 3 keVee)
Resistor backgrounds
~324
Muon induced events in shielding
339 +/- 68
Tritium b-decay
<150
Cavern neutrons from radioactivity
<54
U and Th backgrounds in copper
<9
External cavern neutrons (muon-induced)
<1.4
Old lead (210Pb + daughters)
<0.6
Spontaneous fission neutrons in lead
<0.5
SF neutrons in HDPE
<0.2
HDPE (a,n)
<0.03
8B solar neutrinos
<0.014
Extensive simulations done at PNNL

14. Backgrounds that Modulate: Radon
4/14/2017
Radon levels modulate underground – Measured
Modulation out of phase!
Inner shield is inside a sealed nitrogen purged box
So far it doesn’t look like radon
Bringing grand challenges down to size.
At EMSL, a U.S. Department of Energy national scientific user facility at PNNL, researchers worldwide collaborate in person and remotely. They work together to develop a molecular-level understanding of the physical, chemical, and biological processes that underlie the most critical environmental issues facing the nation. Multi-institutional teams take on grand scientific challenges using suites of diverse, powerful instruments. (EMSL offers a comprehensive collection of unique and state-of-the-art capabilities enabling solutions to problems in the environmental molecular sciences.)
For example, biologists and chemists from six research institutions in the United States and China are investigating a new class of proteins that carry carbon and nitrogen. Harnessing this natural ability could lead to breakthroughs in alternative energy research and greenhouse gas reduction. Among the dozens of instruments applied to this quest are spectroscopy to determine protein structure, imaging techniques to reveal activity inside protein membranes, and high-performance computers to integrate data.
CoGeNT data: Dec March
MINOS data: Averaged
Updated October 2010 | PNNL-SA-70564

15. Backgrounds that Modulate: Muons
4/14/2017
MINOS muon flux modulation measured in Soudan
Approximately +/-1.5%
Peaks three months after best fit to present CoGeNT data
A 1.5% modulation of the estimated 339 +/- 68 muon-induced events in shielding predicts a modulation of 5 events in the keVee energy range
The CoGeNT data set contains 2124 events in the keVee energy range. A 5 event modulation of muon induced events could only produce a 0.2% modulation effect in the CoGeNT data set.
Courtesy Alec T. Habig
PNNL is a partner in education, research, and economic development.
Across Washington, both Battelle and PNNL have invested in science education in our primary and secondary schools, and we continue to host students, high-school level and above, via educational appointments.
We partner with universities and colleges to strengthen our research base and provide opportunities for the up and coming workforce:
University of Washington -- Joint institute for nano-science and technology
University of Maryland – Joint Global Climate Change Research
State of Oregon – Microproducts Breakthrough Institute
The intellectual property developed at PNNL can be designated for use in local and regional partnerships that enhance economic development:
Creates new business starts
Helps existing businesses grow through new and improved products or product lines
Attracts outside businesses into the area
These goals can only be accomplished through teamwork with local and regional economic development agencies, including the Tri-City Industrial Development Council (TRIDEC), Columbia Basin College, Washington State University, PNNL, site contractors, and other entities.
Over the past 13 years, PNNL’s economic development programs have added more than 1,100 jobs and millions of dollars to the economic base of the region. We have provided nearly 800 technology assistance projects to more than 500 technology businesses nationwide since EDO has pressed on with singular focus on our goals: to expand the economy's technology sector and create high-value jobs.
Updated October 2010 | PNNL-SA-70564

16. Surface events and slow pulses
Juan Collar (UC)
Surface events have degraded energy and pile up in the lowest energy bins (like WIMPs)
Surface events (background dominated) on average have slower pulses than bulk events
Rejection between bulk (fast pulses) and surface (slow pulses) gets worse at lower energies
We can estimate the contribution of slow pulses in the data by fitting for the slow and fast pulse distributions
Still looks like there is an excess of events above the expected background

17. The next generation of CoGeNT, CoGeNT-4 (C4)
4/14/2017
The next generation of CoGeNT, CoGeNT-4 (C4)
Four ~1 kg germanium detectors
(unfortunately 4 detectors won’t be funded)
2 inch thick veto panels
Soudan Underground Lab
New DAQ with full energy range
PNNL is a partner in education, research, and economic development.
Across Washington, both Battelle and PNNL have invested in science education in our primary and secondary schools, and we continue to host students, high-school level and above, via educational appointments.
We partner with universities and colleges to strengthen our research base and provide opportunities for the up and coming workforce:
University of Washington -- Joint institute for nano-science and technology
University of Maryland – Joint Global Climate Change Research
State of Oregon – Microproducts Breakthrough Institute
The intellectual property developed at PNNL can be designated for use in local and regional partnerships that enhance economic development:
Creates new business starts
Helps existing businesses grow through new and improved products or product lines
Attracts outside businesses into the area
These goals can only be accomplished through teamwork with local and regional economic development agencies, including the Tri-City Industrial Development Council (TRIDEC), Columbia Basin College, Washington State University, PNNL, site contractors, and other entities.
Over the past 13 years, PNNL’s economic development programs have added more than 1,100 jobs and millions of dollars to the economic base of the region. We have provided nearly 800 technology assistance projects to more than 500 technology businesses nationwide since EDO has pressed on with singular focus on our goals: to expand the economy's technology sector and create high-value jobs.
Updated October 2010 | PNNL-SA-70564

18. Reducing the Background Rate for C4
2 inch veto panels make the muon-induced neutron background negligible
Thicker water shielding reduces the cavern neutron rate + reduces (a,n) from shielding
Electroformed copper used to ease manufacture + has 10 X less background than OFHC
Redesigned frontend will significantly reduce resistor background

19. Expected Background Numbers
CoGeNT (cnts/kg/day)
C-4 (cnts/kg/day)
Resistors
6.2
<1.4
Cu cryostat
5.0 X 10-2
7.0 X 10-3
Muon-induced neutrons in Pb shield
1.9
2.6 X 10-4
Cavern neutrons
3.0 X 10-1
1.3 X 10-3
(a,n) in shielding
2.2 X 10-4
1.3 X 10-4
Total
~10 ~2

20. The background picture for C4
For C4 tritium may be the dominant background—but can be reduced by minimizing surface exposure of crystals
arXiv:

21. What about a single 1 kg crystal?
It we can use the same shield and maintain the predicted background rate things don’t look so bad:
C4 1 kg
C4 4 kg

22. Implications for a low-mass dark matter search with C4
WIMP sensitivity prediction based on likelihood fit to background + WIMP signal
Using conservative background assumptions of some resistor background remaining and 2 years of surface exposure (tritium)
C4 WIMP sensitivity will be very competitive in the low-mass region and complement other experiments in excluding WIMP parameter space
Even a modest lowering of the energy threshold can give a large increase in sensitivity at low masses

23. Future of low-mass dark matter searches
C4 will compliment other low-mass dark matter experiments such as DAMIC, CDMSLite, MAJORANA in excluding parameter space at low masses
For all these experiments it is crucial to have a low threshold and minimize backgrounds

24. Dark Matter analysis with C4
Use all possible information to get the most out of the data: PDFs for signal in energy and time dependence, PDFs for backgrounds in energy and time, constrain backgrounds with measurements outside the signal region, etc.

25. 4/14/2017
Summary
We have done an extensive simulation of the radioactive and cosmogenic backgrounds in the CoGeNT detector arXiv:
So far no explanation for excess at low energies and no candidate for the time dependence of the data
C4 will continue with this technology but increase target mass and reduce backgrounds
The next generation, C4, will address many of the current concerns…2” thick veto panels, improved low-noise design (lower energy threshold), lower background cryostat
C4 will be able to push the limit of sensitivity in the low-mass WIMP parameter space arXiv:
REVENUE NEEDS UDPATED
Mission:
PNNL performs basic and applied research to deliver energy, environmental, and national security for our Nation.
Locations:
In addition to the Richland facilities, PNNL augments its science and technology development capabilities through offices in Seattle and Portland, and at the Sequim Marine Research Operations facility on Washington’s Olympic Peninsula. 25
Updated October 2010 | PNNL-SA-70564

26. Modest neutron rejection with multiple scattering
With 4 detectors we can remove ~40% of neutron energy depositions (multiple scattering)
Neutron deposited energy distribution before coincidence cut
After coincidence cut