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The CoGeNT Dark Matter experiment

Michael G. Marino

23 May 2012

1

Michael G. Marino Neutrinos/DM 24 May 2012

Outline

• Physics

• CoGeNT - Experiment + Technology

• Analysis, recent results

2

Michael G. Marino Neutrinos/DM 24 May 2012

Outline

• Physics

• CoGeNT - Experiment + Technology

• Analysis, recent results

3

Michael G. Marino Neutrinos/DM 24 May 2012

Dark matter• What we know...

4

Michael G. Marino Neutrinos/DM 24 May 2012

Dark matter• What we know...

4

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

5

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

6

P. Fisher

}sensitivity with PPC/CoGeNT

Michael G. Marino Neutrinos/DM 24 May 2012

Annual Rate modulation

7

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

8

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).

9

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

10

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)

12

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)

14

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

16

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)

18

Michael G. Marino Neutrinos/DM 24 May 2012

Ev

en

ts

10

210

310

High Energy

Energy (keV)4 6 8 10 12 14

19

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

21

Michael G. Marino Neutrinos/DM 24 May 2012

2-D Model Visualization

22

Michael G. Marino Neutrinos/DM 24 May 2012

Crosscheck: Lifetimes

23

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

25

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

26

/ 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.

28

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

29

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

30

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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