October 8th, 2009 Sujeewa Kumaratunga 1/27 Recent Progress in PICASSO Sujeewa Kumaratunga for the...
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Transcript of October 8th, 2009 Sujeewa Kumaratunga 1/27 Recent Progress in PICASSO Sujeewa Kumaratunga for the...
Recent Progress in
PICASSO
Sujeewa Kumaratunga
for
the PICASSO collaboration
October 8th, 2009 Sujeewa Kumaratunga 2/22
Outline
PICASSO Introduction Neutron Beam Calibration Data Analysis Results
October 8th, 2009 Sujeewa Kumaratunga 3/22
PICASSO
Project In CAnada to Search for Supersymmetric Objects
or in French
Projet d'Identification de CAndidats Supersymétriques
SOmbres
Université de Montréal - Queen’s University, Kingston - Laurentian
University, Sudbury - University of Alberta - Saha Institute Kolkata, India – SNOLAB - University of Indiana, South Bend - Czech
Technical University in Prague – Bubble Technology Industry, Chalk
River.SNOLAB
October 8th, 2009 Sujeewa Kumaratunga 4/22
CASD : Spin dependent interaction <Sp,n>2
F(q2) : nucl. form facor important for large q2 and large A
Neutralino Nucleon Interaction Crosssections
)(4 2
2
2 qFCMM
MMG A
A
AFA
Enhancement factor General form of cross sections:
CASI : Spin independent – coherent interaction A2
Spin-dependent Spin-independent
How does PICASSO detect Neutralinos (WIMPs)?
October 8th, 2009 Sujeewa Kumaratunga 6/22
How to detect Neutralinos
Weakly Interacting particles Use bubble chamber principal
Minimize background Go underground: shield from Cosmic Rays
(SNOLAB) Use water boxes to shield radioactivity from rock
October 8th, 2009 Sujeewa Kumaratunga 7/22
A bubble forms if:
• particle creates a heat spike
• with enough energy Emin
• deposited within Rmin
The Seitz Theory of Bubble Chambers
Rmin
Pext Pvap
« proto-bubble » minmin ERdx
dEEdep
)(
)(2min TP
TR
2
3
min ))((
)(
3
16
TP
TE
P(T) = superheat (T) = Surface tension = critical length factor = energy convers. efficiency
F. Seitz, Phys. Fluids I (1) (1958) 2
Top
Pvap
Liquid
Tb
Pext Vaporp = Superheat
October 8th, 2009 Sujeewa Kumaratunga 8/22
PICASSO detectors Super heated C4F10 droplets
200μm, held in matrix in polymerized gel act as individual bubble
chambers When neutron interactions
cause 19F recoils or ionizing particle deposits energy Superheated liquid vaporizes
forming small bubbles Bubbles grow explosively (50μs) Turns entire C4F10 droplet to
vapour that resonates Resulting acoustic signal
registered by piezo electric sensors
October 8th, 2009 Sujeewa Kumaratunga 9/22
PICASSO Detector Status
Now Complete 32 detectors, 9 piezos each total active mass of 2248.6g 1795.1g of Freon mass Temperature & Pressure
control system 40 hr data taking 15hr recompression
Neutron Beam Calibration
October 8th, 2009 Sujeewa Kumaratunga 11/22
Calibration with mono-energetic neutrons
neutron induced nuclear recoils similar to WIMPS
n-p reactions on 7Li and 51V targets at 6 MV UdeM-Tandem
threshold measurements in the several keV region
Test Beam Calibration
5 keV
40 keV
50 keV
61 keV
97 keVPro
ba
bili
ty o
f d
ete
ctio
n
Temperature (C)
Theory => detector efficiency
October 8th, 2009 Sujeewa Kumaratunga 12/22
Test Beam Calibration
Detection efficiency (T) Neutralino response (T)
October 8th, 2009 Sujeewa Kumaratunga 13/22
PICASSO detector responses
226Ra spike (200 μm Ø)
AmBe neutrons( data + Monte Carlo)
Recoil nuclei from 50 GeV/c2 WIMP
γ MIP &response
226 Raspike 200)μ mØ(
AmBe neutrons( data + Monte Carlo)
Recoil nuclei from 50 GeV/c2 WIMP
γ MIP &response
PICASSO Data Analysis
October 8th, 2009 Sujeewa Kumaratunga 15/22
PICASSO events
raw signalhigh pass filtered signal
neutrons
noise
different amplitude scales
Take power of signal and integrate to get energy : PVar
October 8th, 2009 Sujeewa Kumaratunga 16/22
PVar Distributions for Calibration Runs
Distributions are temperature dependant
October 8th, 2009 Sujeewa Kumaratunga 17/22
PVar Distributions for neutron and alpha
background
neutronsalphas
Neutrons and alphas well separated
signal
October 8th, 2009 Sujeewa Kumaratunga 18/22
FVar Distributions for neutron and background
Noise
Neutrons (WIMPs) & alphas
Fracture
Blast
October 8th, 2009 Sujeewa Kumaratunga 19/22
Null HypothesisAlpha Rate Fitted: Detectors 71,72
• Rates have been normalized to 19F
72
71
15.171
2
ndf
25.172
2
ndf
PICASSO New Results
October 8th, 2009 Sujeewa Kumaratunga 21/22
PICASSO New Results
σp = - 0.0051pb ± 0.124pb ± 0.007pb (1σ)
90%C.L. limit of σp = 0.16 pb for a WIMP mass of 24 GeV/c2.
13.75±0.48 kg.days
October 8th, 2009 Sujeewa Kumaratunga 22/22
PICASSO Future
PICASSO set up now complete Analysis of the other detectors underway New detector fabrication methods used in some
of the detectors show significant alpha background rejection
Exploit fully our new discrimination techniques to separate signal from noise and background
Scale up to larger detectors 25-100kg
32 det expected sensitivty 0.05 pb
backup
October 8th, 2009 Sujeewa Kumaratunga 24/22
- CDM ?
DIRECT SEARCHES• lab detectors interact with galactic WIMPS• fast WIMPS produce measurable recoils• probe - halo density / structure at solar system
• no signal limits on X-section
• constraints on MSSM parameter space
ACCELERATOR SEARCHES
• no signal limits on mass range
• cannot tell if WIMP is stable
• constraints on MSSM parameter space
Complementarity !!!
• Discovery of cosmol. WIMP does not prove yet SUSY accelerator searches
• LHC signal does not yet prove CDM discovery (in) direct searches
INDIRECT SEARCHES• gravitational trapping (sun, galactic centre etc)• annihilating of slow WIMPS • detection of annihil. products: pairs of , , , Z’s• probe abundance elsewhere• no signal limits on X-section
• constraints on parameter space
October 8th, 2009 Sujeewa Kumaratunga 25/22
Dark Matter - Introduction
What is visible matter? Baryons and radiation
(things that interact electromagnetically)
Only 5% of matter is “visible”
22% of “invisible” universe=> Dark Matter
• What is dark matter?• Discrepancies between
– Temperature and distribution of hot gasses in galaxies and galaxy clusters
and– Rotational speeds of galaxies and
orbital speeds of galaxies in clusters
• Gravitational Lensing
October 8th, 2009 Sujeewa Kumaratunga 26/22
1952 Donald Glaser: “Some Effects of Ionizing Radiation on the
Formation of Bubbles in Liquids” (Phys. Rev. 87, 4, 1952)
1958 G. Brautti, M. Crescia and P. Bassi: “A Bubble Chamber Detector
for Weak Radioactivity” ( Il Nuovo Cimento, 10, 6, 1958)
1960 B. Hahn and S. Spadavecchia “Application of the Bubble
Chamber Technique to detect Fission Fragments” (Il Nuovo
Cimento 54B, 101, 1968)
1993 “Search for Dark Matter with Moderately
Superheated Liquids” (V.Z., Il Nuovo Cimento, 107, 2, 1994)
Superheated Liquids For Particle Detection - timeline
Superheated Liquids & Dark Matter: SIMPLE, COUPP, PICASSO
October 8th, 2009 Sujeewa Kumaratunga 27/22
PICASSO Results
σp = - 0.0051pb ± 0.124pb ± 0.007pb (1σ)
limit of σp = 0.16 pb (90%C.L.) for a WIMP mass of 24 GeV/c2.
13.75±0.48 kg.days (Previous exposure
1.98 kg days)
October 8th, 2009 Sujeewa Kumaratunga 28/22
Lithium (7Li)
Vanadium (51V)528 keV
40 keV
Previous measurements: 7Li target
200 keV < En < 5000 keV.
New measurements: 51V target
5 keV < En < 90 KeV
Target selection
October 8th, 2009 Sujeewa Kumaratunga 29/22
Alpha Neutron Separation
Average of peak amplitudes of 9 transducers (after HP filter)
Signals carry information of the first moments of bubble formation
Why are neutron and alpha signals different in energy? Alphas create multiple nucleation
sites along tracks from ionization; also 1 nucleation at the beginning from recoiling parent nucleus and 1 at end from Bragg peak
Neutron create only 1 nucleation site from the highly localized energy deposition
Is this separation a pseudo effect? No! Neutrons from source are not
symmetrical like alphas – does this have an effect? No!
Could signal from neutrons attenuate over time due to increased vapor bubble formation? No!
neutrons alphas
October 8th, 2009 Sujeewa Kumaratunga 30/22
Some numbers…
6321721Total Number of Events selected with Pvar ,Fvar
7.146.60Exposure (kg.d)
68.97 ±3.565.06±3.2Active Mass F19 per detetctor (g)
103.5101.5Run length (days)
Detector 72Detector 71
October 8th, 2009 Sujeewa Kumaratunga 31/22
Systematics
0.1CTemperature
20%Energy resolution
2%Hydrostatic pressure gradient inside detector
3%Pressure variation
3%Neutron Threshold Energy
5%Active mass (C4F
10)
UncertaintySystematic
October 8th, 2009 Sujeewa Kumaratunga 32/22
PCut= μ− 1 . 64 σ o f G au s sian
What next with PVar?
Use neutron calibration runs to get PVar distributions for neutrons.
Fit a Gaussian and select 95% : this will be our signal
If PVar>PCut => we got particle induced event!!
October 8th, 2009 Sujeewa Kumaratunga 33/22
PICASSO New Results
σp = - 0.0051pb ± 0.124pb ± 0.007pb (1σ)
90%C.L. limit of σp = 0.16 pb for a WIMP mass of 24 GeV/c2.
13.75±0.48 kg.days