COUPP: Bubble Chambers for Dark Matter...

COUPP: Bubble Chambers for Dark Matter Detection

Eric Vazquez Jauregui

SNOLAB

Rencontres de Moriond 2013

La Thuille, Italy; March 9-16, 2013

COUPP bubble chambers

• Target material:superheated CF3Ispin-dependent/independent(C3F8, C4F10)

• Particles interactingevaporate a smallamount of material: bubblenucleation

•Cameras record bubbles

• Piezo sensors detect sound

•Recompression aftereach event 0 3.5 30 500 530

30

70

110

150

190

230 (a) (b) (c) (d)

Mean expansion time, 39.0oC

36.2oC

33.5oC

Max expansion timePre

ssur

e (p

sia)

Elapsed Time (seconds, linear in each region)

Eric Vazquez-Jauregui Moriond 2013 March 14, 2013


• 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 COUPP4

•WIMPs:Nuclear recoilmean free path > 1012 cm1 bubble


COUPP4


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


COUPP4 features

• Energy: threshold detector

•Background suppression:

– UG at SNOLAB

–Water shielding

– Clean materials

•Background discrimination:

– Neutrons:multiples bubblesNuclear recoil, l ∼ 20 cm

– α: acoustic parameterNuclear recoil, 40 µm track

• Large target mass:getting there


COUPP4 at SNOLAB

• Installation in summer 2010

• First Physics run begins Nov.3, 2010(second Physics run in 2012)

•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:

– Neutron calibration runs:AmBe and 252Cf

– Continuous source of 222RnEric Vazquez-Jauregui Moriond 2013 March 14, 2013

COUPP4 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%


COUPP4 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


COUPP4 at SNOLAB: calibrations

Radon fraction = 0.95 ± 0.05222Rn (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

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

100

101

102 15.5 keV11.0 keV7.8 keV

Bubble Multiplicity

Eve

nts

/ kg

/ day

AmBe Data‘Flat’ best fit

Seitz Model‘Exp’ best fit


COUPP4 at SNOLAB: calibrations

• Lower efficiency for 19F and12C recoils

• Seitz model for 127I recoils

SRIM → TRIM calculation

Seitz model:

• 6 keV 19F recoils,C4F10 (PICASSO)

• 101 keV 218Po recoils,C4F10 (PICASSO)

• 101 keV 218Po recoils, CF3I

Understand efficiency for15 keV recoils in CF3I


COUPP4 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)

• 6 events at 8 keV

• 6 events at 10 keV(2 triples)

• 8 events at 15 keV(1 double)

−1 0 1 2 30

20

40

60

80

100

120

ln(AP)

Cou

nts/

0.05

AP

AmBe data sampleWIMP search data

20 recoil− like events

2474alphas

Acousticcut, 96%acceptance

20 WIMP candidates

(Neutrons from rock: < 1/year)


COUPP4 at SNOLAB: results

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

New piezos built(low background salts)

New view-ports(synthetic silica)


COUPP4 at SNOLAB: Physics run II

•New physics run in 2012

• 8 singles, 1 double, 1 triple

Hydraulics failed

Refurbishing the detector

•Replace more components

• ICP-MS assay

Piezos detached from IV

Different target material


COUPP4 at SNOLAB: sensitivity


COUPP60 at SNOLAB


COUPP60

Engineering run at Fermilab:successful commissioning

COUPP60 moved toSNOLAB

•Ready for physics runby the end of the month


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


COUPP4-Lite

•C3F8 as target material

• spin-dependent sensitivity

• Low energy threshold

• new hydraulics

• new pressure vessel

Physics run by mid 2013


COUPP500

•> 1010 γ/β insensitivity

•> 99.3% acoustic αdiscrimination

•Multi-target capabilitySD- and SI-couplingHigh- and low-mass WIMPs

• Easily scalable,inexpensive to replicate

•Growing collaborationNewly merged withPICASSO

R&D phase


COUPP sensitivity plots

WIMP mass [GeV/c2]

SD

WIM

P−

prot

on c

ross

sec

tion

[cm

2 ]

IceCub

e

(χχ→

W+ W

−)(χχ→

bb)COUPP 2012

Super−K (hard)

Super−K (soft)

CMS (A−V)

COUPP−500

250L C 3F 8

, 3 keV

COUPP−4 Lite

PICASSO 2012

101

102

103

104

10−42

10−40

10−38

10−36

WIMP mass [GeV/c2]

SI

WIM

P−

nucl

eon

cros

s se

ctio

n [c

m2 ]

XENON10/100CDMS

CoGent

CRESST

DAMA

COUPP−500250L C3 F

8

3 keV COUPP−500

250L CF 3I, 15 keV

COUPP−60

COUPP 2012COUPP−4 Lite

PICASSO 2012

101

102

103

10−46

10−44

10−42

10−40


Conclusions

• Physics run at SNOLAB completed for COUPP4

– Results published in 2012

– Spin-dependent competitive limit achieved

– Excellent acoustic alpha rejection: > 98.9%

•COUPP family of detectors making huge improvements

– COUPP60 at SNOLAB:Physics run by the end of the month (with 38kg)

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

– COUPP4-Lite: C3F8, by mid this year

– COUPP500 is coming fast


Conclusions

• Physics run at SNOLAB completed for COUPP4

– Results published in 2012

– Spin-dependent competitive limit achieved

– Excellent acoustic alpha rejection: > 98.9%

•COUPP family of detectors making huge improvements

– COUPP60 at SNOLAB:Physics run by the end of the month (with 38kg)

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

– COUPP4-Lite: C3F8, by mid this year

– COUPP500 is coming fast

Stay tuned for more bubbles!


COUPP: Bubble Chambers for Dark Matter...

Documents

Transcript of COUPP: Bubble Chambers for Dark Matter...