The CoGeNT Dark Matter experiment · Michael G. Marino Neutrinos/DM 24 May 2012 Muon modulation • MINOS muon ﬂux modulation measured in Soudan • Approximately +/-1.5% • Peaks

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

2


Outline

• Physics



3


Dark matter• What we know...

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Dark matter• What we know...

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Normal Matter5 %

Dark Matter23 %

Dark Energy72 %


Picture of two colliding galaxy clusters

Green - mass contours from gravitational

lensingColors - X-rays

from hot gas

5

Fig from Clowe et al., Astrophys J. Letters 648

(2006) L109

Dark matter: ‘direct observation’


What about signals?

• Convincing signatures could include:

• Preferred scattering direction

• mass peak (non-WIMP)

• Annual rate modulation

6

P. Fisher

}sensitivity with PPC/CoGeNT


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

http://www.hep.shef.ac.uk/research/dm/intro.php

http://www.hep.shef.ac.uk/research/dm/intro.php


Outline

• Physics



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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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Point-Contact Detectors• P-type Point-Contact (P-PC)

• Geometry: low-capacitance, noise; long charge drift times

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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


t [ns]0 50 100 150 200 250 300 350

310!

AD

C

0

0.01

0.02

0.03

0.04

0.05


t [ns]0 50 100 150 200 250 300 350

310!

AD

C

0

0.01

0.02

0.03

0.04

0.05


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


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


t [ns]0 50 100 150 200 250 300 350

310!

AD

C

0

0.01

0.02

0.03

0.04

0.05


t [ns]0 50 100 150 200 250 300 350

310!

AD

C

0

0.01

0.02

0.03

0.04

0.05


Time (μs)0 40011

AD

C c

ount

s

Unshaped: Pulse-shape analysis

Shaped: Trigger, energy

Detector Signals

ϒ, χ


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


grey vertical wall

Slide: J. Orrell13


Pictures: J. Orrell, E. Fuller

Initial deployment(previous detector)

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E. Fuller, J. Orrell


Outline

• Physics



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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


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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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


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


detector.

... and associated L-capture lines (low energy)

‘Low’ Energy


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


detector.

... and associated L-capture lines (low energy)

‘Low’ Energy


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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2-D Model Visualization

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Crosscheck: Lifetimes

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Co58 Ge68 Cr51 As73 Zn65

Life

time

(day

s)

0

50

100

150

200

250 Expected

Measured

Prelim


Prelim

Model with Oscillation

NULL Model

Raw data

Prelim

Livetime corrected


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


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))


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?


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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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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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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http://prl.aps.org/abstract/PRL/v107/i14/e141301





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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Documents

The CoGeNT Dark Matter experiment · Michael G. Marino Neutrinos/DM 24 May 2012 Muon modulation • MINOS muon ﬂux modulation measured in Soudan • Approximately +/-1.5% • Peaks