the cogent dark matter experiment · michael g. marino neutrinos/dm 24 may 2012 muon modulation •...
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The CoGeNT Dark Matter experiment
Michael G. Marino
23 May 2012
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Michael G. Marino Neutrinos/DM 24 May 2012
Outline
• Physics
• CoGeNT - Experiment + Technology
• Analysis, recent results
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Michael G. Marino Neutrinos/DM 24 May 2012
Outline
• Physics
• CoGeNT - Experiment + Technology
• Analysis, recent results
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Michael G. Marino Neutrinos/DM 24 May 2012
Dark matter• What we know...
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Michael G. Marino Neutrinos/DM 24 May 2012
Dark matter• What we know...
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Normal Matter5 %
Dark Matter23 %
Dark Energy72 %
Michael G. Marino Neutrinos/DM 24 May 2012
Picture of two colliding galaxy clusters
Green - mass contours from gravitational
lensingColors - X-rays
from hot gas
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Fig from Clowe et al., Astrophys J. Letters 648
(2006) L109
Dark matter: ‘direct observation’
Michael G. Marino Neutrinos/DM 24 May 2012
What about signals?
• Convincing signatures could include:
• Preferred scattering direction
• mass peak (non-WIMP)
• Annual rate modulation
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P. Fisher
}sensitivity with PPC/CoGeNT
Michael G. Marino Neutrinos/DM 24 May 2012
Annual Rate modulation
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Figure: http://www.hep.shef.ac.uk/research/dm/intro.php
Interaction rate dependent on relative velocity between detector and DM
Michael G. Marino Neutrinos/DM 24 May 2012
Outline
• Physics
• CoGeNT - Experiment + Technology
• Analysis, recent results
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Michael G. Marino Neutrinos/DM 24 May 2012
Point-Contact Detectors• P-type Point-Contact (P-PC) Germanium
• Geometry: low-capacitance, noise; long charge drift times
Luke et al., IEEE trans. Nucl. Sci. 36 , 926(1989).
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Michael G. Marino Neutrinos/DM 24 May 2012
Point-Contact Detectors• P-type Point-Contact (P-PC)
• Geometry: low-capacitance, noise; long charge drift times
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Michael G. Marino Neutrinos/DM 24 May 2012
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
-0.01
-0.008
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
0.008
Channel: 0, Time (s): 1147.27
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0.022
Channel: 2, Time (s): 1147.27
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
0
0.01
0.02
0.03
0.04
0.05
Channel: 4, Time (s): 1147.27
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
0
0.01
0.02
0.03
0.04
0.05
Channel: 5, Time (s): 1147.27
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
-0.01
-0.008
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
0.008
Channel: 0, Time (s): 1147.27
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0.022
Channel: 2, Time (s): 1147.27
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
0
0.01
0.02
0.03
0.04
0.05
Channel: 4, Time (s): 1147.27
t [ns]0 50 100 150 200 250 300 350
310!
AD
C
0
0.01
0.02
0.03
0.04
0.05
Channel: 5, Time (s): 1147.27
Time (μs)0 40011
AD
C c
ount
s
Unshaped: Pulse-shape analysis
Shaped: Trigger, energy
Detector Signals
ϒ, χ
Michael G. Marino Neutrinos/DM 24 May 2012
CoGeNTCoherent Germanium Neutrino Technology
(and then Dark Matter)
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Located underground (2100
meters water equivalent) to
reduce background from cosmic ray
muons
Michael G. Marino Neutrinos/DM 24 May 2012
grey vertical wall
Slide: J. Orrell13
Michael G. Marino Neutrinos/DM 24 May 2012
Pictures: J. Orrell, E. Fuller
Initial deployment(previous detector)
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Michael G. Marino Neutrinos/DM 24 May 201215
E. Fuller, J. Orrell
Michael G. Marino Neutrinos/DM 24 May 2012
Outline
• Physics
• CoGeNT - Experiment + Technology
• Analysis, recent results
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Michael G. Marino Neutrinos/DM 24 May 201217
Ev
en
ts
10
210
310
High Energy
Energy (keV)4 6 8 10 12 14
Even
ts
0
20
40
60
80
100
120
140
160
180
200
220
Low energy
Energy (keV)0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
• What we have:
• Energy, Time data over two channels:
• 0.4 → 3 keV
• 0.4 → 14 keV
• 4 Dec 2009 - 6 Mar 2011
• 442 live days, 458 days span
Extracting Physics
Michael G. Marino Neutrinos/DM 24 May 2012
Extracting Physics
• Energy spectrum (e.g. WIMP exclusion)
• PRL 106, (2011) 131301.
• Time (+ energy) spectrum (modulation)
• Subtraction analysis (U Chicago)
• 2-D ML fit analysis (U Washington)
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Michael G. Marino Neutrinos/DM 24 May 2012
Ev
en
ts
10
210
310
High Energy
Energy (keV)4 6 8 10 12 14
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73As
68Ge68Ga65Zn
58Co
55Fe54Mn
49V
Peaks are from electron-capture of cosmogenic isotopes in the
detector.
Each have K-capture lines
(higher energy)...
‘High’ Energy
Michael G. Marino Neutrinos/DM 24 May 201220
Ev
en
ts
0
20
40
60
80
100
120
140
160
180
200
220
Low energy
Energy (keV)0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
Peaks are from electron-capture of cosmogenic isotopes in the
detector.
... and associated L-capture lines (low energy)
‘Low’ Energy
Michael G. Marino Neutrinos/DM 24 May 201220
Ev
en
ts
0
20
40
60
80
100
120
140
160
180
200
220
Low energy
Energy (keV)0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
68Ge
65Zn
All the rest
Peaks are from electron-capture of cosmogenic isotopes in the
detector.
... and associated L-capture lines (low energy)
‘Low’ Energy
Michael G. Marino Neutrinos/DM 24 May 2012
Time analysis
• 2-D time vs. energy analysis
• Simultaneous Max-likelihood fit over 2 channels
• Constrain L/K electron-capture peaks by their well-measured ratios
• Add oscillation PDF in low-energy channel
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Michael G. Marino Neutrinos/DM 24 May 2012
2-D Model Visualization
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Michael G. Marino Neutrinos/DM 24 May 2012
Crosscheck: Lifetimes
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Co58 Ge68 Cr51 As73 Zn65
Life
time
(day
s)
0
50
100
150
200
250 Expected
Measured
Prelim
Michael G. Marino Neutrinos/DM 24 May 201224
Prelim
Model with Oscillation
NULL Model
Raw data
Prelim
Livetime corrected
Michael G. Marino Neutrinos/DM 24 May 2012
Phase vs. Period
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Period (Years)0.5 1 1.5 2 2.5 3
Phas
e
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Prelim
Best fit point:
Phase: 49.9 d (Min ~23 Oct)
Period: 339.5 d
1 σ2 σ
Michael G. Marino Neutrinos/DM 24 May 2012
Significance
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/ ndf 2r 93.3 / 40norm 0.0052± 0.4531 k 0.024± 3.677
(A=0))max - ln Lmax2*(ln L0 2 4 6 8 10 12 14 16 18 20 22
Rel
ativ
e co
unts
-410
-310
-210
-110
/ ndf 2r 93.3 / 40norm 0.0052± 0.4531 k 0.024± 3.677
Prelim
• Generate many toy models of NULL hypothesis, fit to signal + background, calc:
Fit to χ2 dist
2 (logL(B)
max
� logL(B = 0))
Michael G. Marino Neutrinos/DM 24 May 2012
Fit summary
• ML fit (Prelim)
• Min 23 Oct, Period: 339.5 d, Ampl: 17.7 ± 6.5%, significance 94.6%
• Subtraction (U Chicago, arXiv:1106.0650)
• Min 16 Oct ± 12 d, period 347 ± 29 d, Ampl: 16.6 ± 3.8%, significance 99.4%
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But what is it?
Michael G. Marino Neutrinos/DM 24 May 2012
Muon modulation• 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 0.5-3 keVee energy range
Courtesy Alec T. Habig
Slide: M. Kos, PNNL
• The CoGeNT data set contains 2124 events in the 0.5-3 keVee energy range. A 5 event modulation of muon induced events could only produce a 0.2% modulation effect in the CoGeNT data set.
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Michael G. Marino Neutrinos/DM 24 May 2012
Radon Modulation• Radon levels modulate
underground – Measured by MINOS
• Modulation out of phase!
• Also: Look at data out to 300 keV
• Infer the maximum number of events due to Rn in the data
• 2.8 events in 0.5 – 3.0 keV
CoGeNT Data
Slide: M. Kos, PNNL
Prelim
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Michael G. Marino Neutrinos/DM 24 May 2012
Summary• Recent CoGeNT data consistent with an
annual modulation at low energies, PRL 107 (2011) 141301, this is confirmed by two fully independent analyses
• Background analyses suggest muons and Rn can not account for this modulation, still investigating other possibilities
• Longer paper in preparation detailing analysis
• Detector is back up and running, data not yet analyzed, planned to open June 2012
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Michael G. Marino Neutrinos/DM 24 May 2012
CoGeNT collaborationC.E. Aalseth,1 P.S. Barbeau,2 J. Colaresi,3 J.I. Collar,2 J. Diaz Leon,4 J.E. Fast,1 N. Fields,2
T.W. Hossbach,1, 2 M.E. Keillor,1 J.D. Kephart,1 A. Knecht,4 M.S. Kos,1 M.G. Marino,4
H.S. Miley,1 M.L. Miller,4 J.L. Orrell,1 D.C. Radford,5 J.F. Wilkerson,6 and K.M. Yocum3
(CoGeNT Collaboration)1Pacific Northwest National Laboratory, Richland, WA 99352, USA
2Kavli Institute for Cosmological Physics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA3CANBERRA Industries, Meriden, CT 06450, USA
4Center for Experimental Nuclear Physics and Astrophysics and Departmentof Physics, University of Washington, Seattle, WA 98195, USA5Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
6Department of Physics and Astronomy, University of North Carolina, NC 27599, USA
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