Bubble Chambers for Direct Dark Matter Searches in...

Bubble Chambers for Direct Dark Matter Searches in COUPP

Eric Vazquez Jauregui

SNOLAB

8th Patras Workshop on Axions, WIMPs and WISPs

Chicago IL, USA; July 22, 2012

Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012

COUPP bubble chambers

• Target material:superheated CF3I

spin-dependent/independent

• Particles interactingevaporate a smallamount of material: bubblenucleation

• Cameras record bubbles

• Piezo sensors detect sound

• Recompression aftereach event



• The ability to reject electron and gamma backgrounds byarranging the chamber thermodynamics such that theseparticles do not even trigger the detector

• The ability to suppress neutron backgrounds by having theradioactively impure detection elements far from the activevolume and by using the self-shielding of a large device andthe high granularity to identify multiple bubbles

• The ability to build large chambers cheaply and with achoice of target fluids

• The ability to increase the size of the chambers withoutchanging the size or complexity of the data acquisition

• Sensitivity to spin-dependent and spin-independent WIMPcouplings


Bubble nucleation

Dependence of bubblenucleation on the total

deposited energy and dE/dx

• Region of bubble nucleationat 15 psig

• Backgrounds:electrons, 218Po, 222Rn

• Signal processes ofIodine, Fluorine and Carbonnuclear recoils insensitive to

electrons and gammas



• Alpha decays:Nuclear recoil and40 µm alpha track1 bubble

• Neutrons:Nuclear recoilsmean free path ∼20 cm3:1 single-multiple ratioin COUPP 4kg

• WIMPs:Nuclear recoilmean free path > 1012 cm1 bubble


COUPP-4kg


COUPP at SNOLAB

SNOLAB

deepest and cleanestlarge-space internationalfacility in the world

• 2 km undergroundnear Sudbury, Ontario

• ultra-low radioactivitybackground environmentClass 2000

• Physics programme focusedon neutrino physicsand direct dark mattersearches


COUPP at SNOLAB


COUPP-4kg features

• Energy: threshold detector

• Background suppression:

– UG at SNOLAB

– Water shielding

– Clean materials: almostthere

• Background discrimination:

– Neutrons:multiples bubblesNuclear recoil, l ∼ 20 cm

– α: acoustic parameterNuclear recoil, 40 µm track

• Large target mass:getting there


COUPP-4kg more features

• Thermodynamics: two temperature sensors and pressuretransducers

• Fast AC-coupled pressure transducer for bubble growth

• Four lead zirconate piezoelectric acoustic transducers

• Two VGA resolution CCD cameras(20-degree stereo angle, 100 frames per second)

• Main trigger: frame-to-frame differences

– compression within 20 ms of a bubble nucleation

– 500 secs of expansion without a bubble −→

compress to 215 psia for 30 secs

– live-time: starts 30 secs after an expansion


COUPP-4kg at SNOLAB

• Installation in summer 2010

• Physics run begins Nov. 3,2010

• Run settings (P=30.5 psia):

– 17.4 days at 8 keV (39oC)

– 21.9 days at 10 keV (36oC)

– 97.3 days at 15 keV (33.5oC)

• 4.048 kg of CF3I

• Calibrations:

– 12 neutron calibration runs:AmBe and 252Cf

– Continuous source of 222Rn


COUPP-4kg at SNOLAB: data analysis

• Examination of images:algorithm searching forclusters among pixels thatchanged between consecutiveframes

• Examination of pressure rise:fit to the rate of pressurerise by a quadratic timedependence for bubbles inthe bulk

• Examination of the acousticsignal

hand-scanned toresolve disagreement

overall efficiency for all data qualityand fiducial volume cuts is 82.5 ± 1.9%


COUPP-4kg at SNOLAB

Acoustic transducer signalsdigitized with a 2.5 MHz

sampling rate and recordedfor 40 ms for each event

3 ways of counting:

• Images: cameras

• Pressure rise: transducer

• Acoustic parameter: piezos

The nuclear recoil acceptanceof the AP cut 95.8 ± 0.5%

0 0.5 1 1.5 2 2.5 3 3.5 4 4.50

1

2

3

4

5

6

7

8

Bubble Number (pressure rise)A

cous

tic P

aram

eter

Background data, nbub = 1

AmBe data, nbub = 1

AmBe data, nbub = 2

AmBe data, nbub = 3

AmBe data, nbub = 4

Single bubble, recoil−like events

Alphas


COUPP-4kg at SNOLAB: calibrations

Neutron calibrations:

• AmBe

•252Cf

100 150 200 250 300 3500

20

40

60

80

100

120

140

160

180

Days since start of run

Cou

nts/

kg/d

ay

AmBe source data stability

One bubbles

Two bubbles

Three bubbles

Recoil−like events

50 100 150 200 250 300 3500

2

4

6

8

10

12

Days since start of run

Cou

nts/

kg/d

ay

Alpha data stability

One bubblesRecoil−like events

Alpha calibration: 222Rn

• Test Seitz model threshold

• Absolute bubble nucleationefficiency

• Characterize acousticsignature of α decays



Radon fraction = 0.95 ± 0.05

222Rn (101 keV)218Po (112 keV)214Po (146 keV)

100

101

102

103

10−5

10−4

10−3

10−2

10−1

Time between bulk singles (minutes)

Cou

nt r

ate

(nor

mal

ized

to 1

)

34 C data

Best fit simulation (Radon fraction = 0.95 ± 0.05)

Radon fraction = 0

0 50 100 150 200 2500

2

4

6

8

Seitz threshold (keV)

0

10

20

30

40

Rat

e (c

ts/d

ay)

Alpha data (34 C)Alpha pairsRadon model prediction



GEANT and MCNPsimulations

• Bubble rate is 50% higher

• Multiple bubbles rate alsohigher

x1 x2 x3 x4 x1 x2 x3 x4 x1 x2 x3 x4

100

101

102 15.5 keV11.0 keV7.8 keV

Bubble MultiplicityE

vent

s / k

g / d

ay

AmBe Data‘Flat’ best fit

Seitz Model‘Exp’ best fit



• Lower efficiency for 19F and12C recoils

• Seitz model for 127I recoils

SRIM → TRIM calculation



Seitz model:

• 6 keV 19F recoils in C4F10(PICASSO)

• 101 keV 218Po recoils inC4F10 (PICASSO)

• 101 keV 218Po recoilsin CF3I

Understand efficiency for15 keV recoils in CF3I

Measurements havebeen performed


COUPP-4kg at SNOLAB: results

456 kg-days

2474 alphas1733 alphas (15 keV data)

5.3 alpha decays/ kg-day95% from radon

> 98.9% α rejection> 99.3% (15 keV data)



20 WIMP candidates

• 6 events at 8 keV

• 6 events at 10 keV(2 triples)

• 8 events at 15 keV(1 double)

Neutrons from rock:< 1/year



Some events with high AP



Clustered:3 high-AP events

in one hourat 8 keV

Significant fractioncorrelated in time



Internal neutron background

• View-ports:0.5 ppm 238U and 0.8 ppm232Th(∼ 5 events)

• Piezos:4.0 ppm 238U, 1.9 ppm 232Thand 210Pb(∼ 2 events)

Fission and (α,n)on light elements


COUPP-4kg at SNOLAB: upgrades

New piezos built(low background salts)

New view-ports(synthetic silica)

Physics run restarted last month!


COUPP-4kg at SNOLAB: sensitivity

WIMP Mass (GeV)

Spi

n−de

pend

ent p

roto

n cr

oss−

sect

ion

(cm

2 )COUPP (J

an. 2011)

KIMS (2

007)

PICASSO (2009)

(χχ→

W+W−

)

(χχ→

bb)

SIMPLE (2

010)

SIMPLE (2011)

COUPP (this r

esult)

IceCub

e

Super−K (hard)

CO

UPP

(Jan. 2011)PICASSO

(2012)

cMSSM

(χχ→

W+W−

)

(χχ→

bb)

SIMPLE (2011)

COUPP

(this r

esult)

Super−K (soft)

CDF (A−V Eff. theory)

CDF (A−V 100 GeV med.)

CMS

SIMPLE (2

012)

101

102

103

10410

−40

10−39

10−38

10−37

10−36


COUPP-4kg at SNOLAB: sensitivity

http://dmtools.brown.edu/ Gaitskell,Mandic,Filippini

WIMP Mass (GeV)

Spi

n−in

depe

nden

t nuc

leon

cro

ss−

sect

ion

(cm

2 )

XENON10

CDMS

CDMS (SUF)

XENON100

COUPP (Jan. 2011)

COUPP (this result)

cMSSM

101

102

10310

−45

10−44

10−43

10−42

10−41

10−40


COUPP-60kg


COUPP-60kg

Engineering run at Fermilab:successful commissioningCOUPP-60kg is moving

to SNOLAB

• Ready for physics runby the end of this year


Calibrations

• γ and neutron calibrations

– AmBe and 252Cf

– 60Co and 133Ba

• COUPP Iodine RecoilThreshold Experiment

– Low energy Iodine recoils

– π beam andsilicon trackers

•88Y/Be calibration chamber

– Understand response to lowenergy recoils

– Monochromatic low energyneutrons


COUPP-500kg

• A tonne scale detector

• spin-independent sensitivity9 × 10−47cm2, background-free year running

• Beyond next generation (G2)device

• <5M total cost

• Possible to use alternativefluids (C4F10)

R&D phase


COUPP-60kg-500kg expected sensitivity at SNOLAB

WIMP Mass (GeV)

Spi

n−de

pend

ent p

roto

n cr

oss−

sect

ion

(cm

2 )

SIMPLE (2011)

IceCube

Super−K (hard)

COUPP (Jan. 2011)

cMSSM

(χχ→

W+ W

−)

(χχ →bb)

SIMPLE (2010)

SIMPLE (2011)

COUPP (Apr. 2012)

Super−K (soft)

COUPP−4, 4 mo, 0 bg


COUPP−60, 1 yr, 0 bg

COUPP−500, 1 yr

PICASSO (2012)

CMS

101

102

103

10410

−42

10−40

10−38

10−36


COUPP-60kg-500kg expected sensitivity at SNOLAB

WIMP Mass (GeV)

Spi

n−in

depe

nden

t cro

ss−

sect

ion

(cm

2 )

XENON10

CDMS

CDMS (SUF)

XENON100

COUPP (Jan. 2011)

COUPP (Apr. 2012)



COUPP−60, 1 yr, 0 bg

COUPP−500, 1 yr

cMSSM

101

102

10310

−47

10−46

10−45

10−44

10−43

10−42

10−41

10−40


Conclusions

• First physics run at SNOLAB completed for COUPP-4kg

– Results submitted for publication

– Spin-dependent competitive limit achieved

– Excellent acoustic alpha rejection

– Upgraded detector running

• COUPP family of detectors making huge improvements

– COUPP-60kg getting to SNOLAB,Physics run by the end of the year

– Calibrations, calibrations and calibrations:CIRTE, 88Y/Be, ...

– COUPP-500kg is coming fast


Conclusions

• First physics run at SNOLAB completed for COUPP-4kg

– Results submitted for publication

– Spin-dependent competitive limit achieved

– Excellent acoustic alpha rejection

– Upgraded detector running

• COUPP family of detectors making huge improvements

– COUPP-60kg getting to SNOLAB,Physics run by the end of the year

– Calibrations, calibrations and calibrations:CIRTE, 88Y/Be, ...

– COUPP-500kg is coming fast

Stay tuned for more bubbles!


Bubble Chambers for Direct Dark Matter Searches in...

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