Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP bubble chambers
• 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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP bubble chambers
• 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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP at SNOLAB
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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%
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg at SNOLAB: calibrations
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg at SNOLAB: calibrations
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg at SNOLAB: calibrations
• Lower efficiency for 19F and12C recoils
• Seitz model for 127I recoils
SRIM → TRIM calculation
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg at SNOLAB: calibrations
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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)
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg at SNOLAB: results
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg at SNOLAB: results
Some events with high AP
• 4 events at 8 keV
• 2 events at 10 keV
Clustered:3 high-AP events
in one hourat 8 keV
Significant fractioncorrelated in time
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg 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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-4kg at SNOLAB: upgrades
New piezos built(low background salts)
New view-ports(synthetic silica)
Physics run restarted last month!
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-60kg
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
COUPP-60kg
Engineering run at Fermilab:successful commissioningCOUPP-60kg is moving
to SNOLAB
• Ready for physics runby the end of this year
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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, 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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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−4, 4 mo, 0 bg
COUPP−60, 4 mo, 0 bg
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012
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!
Eric Vazquez-Jauregui PATRAS 2012 July 22, 2012