recent results of the cogent dark matter experiment · • geometry: low capacitance, low noise;...

Recent results of the CoGeNT Dark Matter experiment

Michael G. MarinoCoGeNT Collaboration

Technische Universität München

Moriond EW 20125 Mar 2012

Michael G. Marino Moriond EW, 5 Mar 2012

Outline

• Physics

• CoGeNT - Experiment + Technology

• Analysis, recent results

2

Michael G. Marino Moriond EW, 5 Mar 20123

DM Signals

• Convincing signatures could include:

• Preferred scattering direction

• mass peak (non-WIMP)

• Annual rate modulation

P. Fisher

}sensitivity with P-PC/CoGeNT

Michael G. Marino

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

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

Luke et al., IEEE trans. Nucl. Sci. 36 , 926(1989).

4 Moriond EW, 5 Mar 2012

Michael G. Marino

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

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


Michael G. Marino

P-PC Detector Physics Reach

• Low noise, low threshold (< 1keV)

• Excellent energy resolution

• Low-energy physics (<1 - 10s keV)

6

Aalseth, et al., PRL 101, 251301 (2008)

Moriond EW, 5 Mar 2012

http://dx.doi.org/10.1103/PhysRevLett.101.251301


Michael G. Marino

Dark Matter Limits

7

CDMS, 612 kg-d

CoGeNT, 8.4 kg-d

CDMS Collaboration, arXiv:0912.3592; Aalseth, et al., PRL 101, 251301 (2008); DAMA Collaboration, EPJ C56 (2008), 333, arXiv:0804.2741Edelweiss-II, arXiv:1103.4070

DAMA, 820 kg-yr, 3σ allowed region




Michael G. Marino

CoGeNTCoherent Germanium Neutrino Technology

(and then Dark Matter)

8

• 1st detector - DM(Tunnel and Reservoir Plan, TARP)

PRL 101, 251301 (2008)

• 2nd detector (R&D) -Soudan

• 3rd (current) detector (DM) - Soudan PRL 106, (2011) 131301




http://prl.aps.org/abstract/PRL/v106/i13/e131301


Michael G. Marino 9

E. Fuller, J. OrrellMoriond EW, 5 Mar 2012

Michael G. Marino

NIM Crate

Detector Preamp

777 (fast)Amp

Spec (shaping)

Amp

NI Digitizer

High gain

Low gain

Low gain

High gain

Muon Veto

10

What do we read out?

Only charge!


Michael G. Marino 11

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

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

310!

AD

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

310!

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-0.01

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-0.006

-0.004

-0.002

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0.002

0.004

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0.008


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

310!

AD

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

310!

AD

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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)0 400

AD

C c

ount

s

Unshaped: Pulse-shape analysis

Shaped: Trigger, energy


Michael G. Marino Moriond, 5 Mar 201212

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Energy (keV)2 4 6 8 10 12 14

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Energy (keV)1 1.5 2 2.5 3

Two energy channels

• Peaks in data arise from L-/K-electron-capture decays of cosmogenics

• Peaks are centered at the L/K characteristic energies of the daughter nuclei

Data output

Michael G. Marino

Analysis cuts

• Three cuts:

• Liquid Nitrogen fills

• Microphonics cuts - analyze ratios of shaped channels (Morales, et al., NIM A 321 (1992) 410)

• Rise-time cuts - Previous results indicated slow-pulse ‘contamination’


Michael G. Marino

Rise-time vs. Energy

14

Energy (keV)0 10 20 30 40 50 60 70 80

s)µ

10-9

0 R

iset

ime

(

0

1

2

3

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6

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8

9

10

1

10

210

310

410

510

Incomplete charge collection near the dead layer

t [ns]0 5000 10000 15000 20000 25000

Volta

ge (V

)

-0.03

-0.025

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

s): 1.164833, Amplitude (keV): 0.855480µRise time (

t [ns]0 5000 10000 15000 20000 25000

Cur

rent

(a.u

.)

-0.0014

-0.0012

-0.001

-0.0008

-0.0006

-0.0004

-0.0002

0

Savitzky-Golay Derivative Moriond EW, 5 Mar 2012

Michael G. Marino

Extracting Physics

• Energy spectrum (e.g. WIMP exclusion)

• PRL 106, (2011) 131301.

• Time (+ energy) spectrum, look for modulation

• Subtraction analysis (U Chicago)

• 2-D ML fit analysis (U Washington)




Michael G. Marino

Data set

• 4 Dec 2009 - 6 Mar 2011 (just before Soudan fire)

• 442 live days, 458 days span

• 3 periods of down time (lab-scheduled maintenance)


Michael G. Marino

Time analysis

17

• 2-D time vs. energy analysis across both channels

• Constrain L/K electron-capture peaks by their well-measured ratios

• Add floating oscillation PDF in low-energy channel


Ev

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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

68Ge65Zn

All the rest


Ev

en

ts

10

210

310

High Energy

Energy (keV)4 6 8 10 12 14

73As

68Ge68Ga65Zn

58Co

55Fe54Mn

49V

Energy Channel

Prelim


Michael G. Marino

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

Time channel


Michael G. Marino

Phase vs. Period

21

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

Fit summary

• ML fit

• Min 23 Oct, Period: 339.5 d, Ampl: 17.7 ± 6.5 %, significance 94.6%

• Subtraction (PRL 107 (2011) 141301)

• Min 16 Oct ± 12 d, period 347 ± 29 d, Ampl: 16.6 ± 3.8 %, significance 99.4%




Michael G. Marino

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.


Michael G. Marino

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


Michael G. Marino

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






Michael G. Marino

CoGeNT collaboration

26

C.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


Extra Slides


Significance

28

/ 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))


Analysis Tools

• pyWIMP - Extensions to RooFit for 1-,2-D (Energy/Time) DM fitting

• Tools - Generic oscillations, WIMP models, efficiently deal with data-taking gaps

• Available: http://github.com/mgmarino/pyWIMP

Energy (keV)

0 0.5 1 1.5 2 2.5 3 Time (years)

01

23

4

(cou

nts/

keV/

kg/y

r/pb)

-1m

dEdR 1

10

210

310

2-D PDF of 10 GeV WIMP in Ge


http://github.com/mgmarino/pyWIMP




Background estimates

Backgrounds in low-energy region (0.5 – 3 keVee)

Cavern neutrons (from radioactivity)Tritium β-decay

Muon-induced neutrons

Background sum

PRELIMINARY

Slide: M. Kos, PNNL

Muon-induced neutrons temporal variation

Muon veto cut is not applied in modulation analysis

Veto does not change energy spectrum after dead time correctionVeto efficiency fluctuations might lead to false modulation

Applying muon veto does not remove the modulation

Just reduces event rangeMINOS muon flux modulation measured in Soudan

Approximately +/-1.5%Peaks three months after best fit to present CoGeNT data.Including simulated muon-induced neutron component lessons the ~1.5% muon modulation

Courtesy Alec T. Habig

PRELIMINARY

Slide: M. Kos, PNNL

Rise-time Studies


Rise-time studies, estimating efficiencies

34

Simulate pulses (shape,

noise, etc.)

Run through Analysis

chain

Derive cut acceptances

Check against data


Check cut against data• Take cut

• Fit spectrum (peaks + exponential + flat background)

• Extract component amplitude information

35

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Energy (keV)2 4 6 8 10 12 14


Check cut against data• Take cut

• Fit spectrum (peaks + exponential + flat background)

• Extract component amplitude information

35

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Energy (keV)2 4 6 8 10 12 14

68Ge65Zn

65Zn 68Ga68Ge

73As


20% 30% 40% 50% 60% 70% 80% 90% 95% 99% LN+micro

(Rel

ativ

e Ef

ficie

ncy)

/(Est

imat

ed E

ffici

ency

)

0

0.5

1

1.5

2

2.5

3Zn (8.98 keV)65

As (11.1 keV)73

Ga (9.66 keV)68

Ge (10.37 keV)68

36

Check cuts against data


20% 30% 40% 50% 60% 70% 80% 90% 95% 99% LN+micro

(Rel

ativ

e Ef

ficie

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ffici

ency

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Ge (1.3 keV)68

Zn (1.1 keV)65


37


20% 30% 40% 50% 60% 70% 80% 90% 95% 99% LN+micro

(Rel

ativ

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ficie

ncy)

/(Est

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ency

)

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Flat bkgd component

Exponential bkgd component


38


Rise-time summary

• Sim used to derive cut acceptances

• Efficiency of cuts cross-checked using peaks, work well to at least 1 keV

• Fiducial volume cut: 0.4 → 0.33 kg active mass

39

Stability Studies


Stability

41

arXiv:1106.0650

Trigger, noise


Axioelectric Limits

42

Axion Mass (keV)1 10

eeag

-1310

-1210

-1110

-1010

-910

siSolar

Globular Clusters

DAMA (Corrected)CDMS 2009CoGeNT 2008This result

CDMS: PRL 103 (2009) 141802Solar neutrinos: PRD 79 (2009) 107301Globular clusters PRD 51 (1995) 1495

WIMP (Energy only)


Extracting WIMP limits

44

Energy (keV)0.5 1 1.5 2 2.5 3 3.5

Energy (keV)0.5 1 1.5 2 2.5 3 3.5

Cou

nts/

keV/

kg/d

0

5

10

15

20

25

30

35

40

45

• ML-based exclusion calculation

• Background uncertainty handled as nuisance pars:

Rolke, et al., NIM A 551 (2005) 493 90% CL exclusion of 8 GeV WIMP


Low-mass WIMP limits

45

WIMP Mass [GeV/c2]

Cro

ssïs

ectio

n [c

m2 ] (

norm

alis

ed to

nuc

leon

)

100 101 10210ï42

10ï41

10ï40

10ï39

10ï38

CDMS, 612 kg-d

CDMS Collaboration, arXiv:0912.3592; DAMA Collaboration, EPJ C56 (2008), 333, arXiv:0804.2741

DAMA, 820 kg-yr,3σ, 5σ allowed

region

Black (49.7 kg-d): solid 70% RT cutdashed 95% RT cut

recent results of the cogent dark matter experiment · • geometry: low capacitance, low noise;...

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