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The PicassoExperiment
Plans and Results
The PicassoExperiment
Plans and ResultsCarsten Krauss
Queen s UniversityCarsten Krauss
Queen s University
January 24, 2006University of Pennsylvania
January 24, 2006University of Pennsylvania
Overview
Dark Matter
Superheated Droplet Detector
Prototype run results
SNOLAB
PICASSO 32
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PICASSO
Project In CAnada to Search forSupersymmetric Objects
Detect recoils of spin-dependentinteractions with dark matter particles
Picasso Collaboration
Indiana University at South Bend
I. Levine, W. Feighery, J. Nuerenberg, E. Behnke, C. Muthusi
Université de Montréal
V. Zacek, L. Lessard, C. Leroy, G. Azuelos, J.-P. Martin, U. Wichoski, P. Doane, R. Gornea, M. Bernabe-Heider, M. H. Genest, R. Guenette, F. Aubin, Y. Landry, N. Starinski, G. Richard
Prague Technical University
S. Pospisil, I. Stekl, J. Sodomka, J. Bocan
Queen s University
A. J. Noble, C. B. Krauss, X. X. Dai, K. Clark, C. Storey, C. Hearns
University of Pisa
S. Shore
Yale University
F. d'Errico
Universita di Lisboa
T. Girard, F. Giuliani, T. Morlat, J. G. Marques, A. Fernandes, R. Martins, M. Da Costa
Paris VI, VII
G. Waysand, D. Limagne
Dark Matter
First hints aboutdiscrepancy incosmological observationsin 1933
Since then more data takenand more hints forexistence of dark matterhave been found
Dark Matter II
WMAP microwave background picture
suggests flatness of universe and thereforelarger matter density than seen
2
Dark Matter III
Cosmological pictureis consistent andpoints towards amissing piece in theunderstanding of theworld
Hardly anyone islooking for anythingbut prove for theexistence of darkmatter
Dark Matter SearchAnnihilation Signal search
Alternative to direct observations isobservation of annihilation signal which ispredicted to occur mainly at galactic cores
Satellite based gamma ray telescopes likeEGRET have not seen conclusive signals
Promising new experiment GLAST mightchange the picture
Super-Symmetry and DarkMatter
Dark matter particle can very likely be the LSPor Neutralino
Interesting convergence between interests ofSUSY theorists and cosmological dark matter
Recoil Signal
WIMP only interacts by elastic nuclear recoils
For spin dependent interactions Fluorine is the mostfavourable target material because its nuclear matrixelement is the largest
Recoil energy in keV rangeExpect less than 1 count/day/kg active mass
Superheated Droplets
Freon droplets suspended in gelmatrix
Each droplet is like a mini-bubblechamber
Nuclear recoils trigger phase transition
Fluorine recoil track
Freon dropletNucleation cores
Detector PrincipleSDDs originally developed for neutron dosimetryand are in use at nuclear facilities
Active material is C4F10 in superheated form
Only fissions, alphas and nuclear recoils are detected
Insensitive to minimally ionizing particles andgammas
Seitz bubble chamber limit:
critical energy inside critical radius leads toformation of bubble in superheated medium
3
Superheated DropletDetector
Bubble size is crucial for background rate andsensitivity
Average bubble size increased by factor of sixsince
Detector
Contains gel matrix to keepsuperheated bubblessuspendedUse CsCl to match density ofbubbles to gel
Started feasibility studies withcommercial 5ml detectors
inceased size and purity since
Signal Processing
acoustic shock-wave is picked up bypiezo
Typical bubble signal sampled with960kHz (4096 samples)
Filter & Event Selection
2 dimensional Fourier transformation used to distinguishbubbles from background noise
If enough power is concentrated in trigger window andfrequency range 20-90kHz, signal is identified as bubble
Filter Efficiency
Filter has been tested over fulltemperature range
Response is fairly high and uniform
includes trigger efficiency
Calibration
Tandem acceleratorin Montreal used tocalibrate detectorswith mono-energeticneutrons (7Li(p,n)reaction)
Beam-line upgradedto run with lowerenergy, narrowerenergy spread
4
Neutron Calibration
Neutron cross-section well known,modeled and reproduced in detectorresponse
Temperature Dependence
Threshold and response changes withtemperature
Detection Threshold
Detector only becomes sensitive to background at hightemperatures
-particles are a problem over the entire range of operation
Alpha Response
Spiked detector gives alpha response
Identical results from Ac and Th spike
Extremely important input for understanding ofbackground
Gamma Response
Response curve modeled well
(This is the response for another type ofdetector with a different gas mixture)
Successful Purification
Development since the start ofpurification efforts
5
Internal Background
This is the most difficult challengePICASSO faces for the next steps
Currently purifying detectoringredients with methods developedby SNO and refined for PICASSO
New and more efficient methods areneeded
Radiopurity
Most critical single problem:
Internal activity from CsCl has to be purified
Two possible ways: Replacing CsCl salt - breakthrough inpurification
Raw Salt Measured U
U CriteriaTh Criteria
Raw Salt Measured Th
As built detectors II, UPurifiedsalt. U
RadiopurityStatus: Improvement by
better handling(cleanroom,procedures)
larger size handlingsystem, cover gassystem
New method ofpurification
Problem: long turn-around times
Large scale purificationsystem for SDD ingredients
in Montreal
Spacial Reconstruction
Very promisingstudies toreconstruct thelocation of theexploded bubble tobe able to suppresshot-spots andsurface events
(Here only 4 piezos,final new detectorswill have up to 9)
Sudbury
Sudbury, Ontario
Installation At SNO
SNO kindly agreed tohost PICASSO in thewater area
We re in the fortunatesituation to use to onlyfree space at the lab
Still the guest statusrequires extra thoughtand effort
6
Data Taking in 20040.27 µ/m2/day
6 1 liter detectors were operatedfor 7 months
2 independent temperaturecontrol systems
2 readout channels for eachdetector
1 foot water cubes for neutronshielding
4096 12bit samples for eachtrigger with a sampling rate of960kHz
Data taken remotely
60t tank area in the SNOwater utility area
SNO Phase Detector
1 liter containers
SNO developed polypropylen
Mineral oil between gel and pressureline
Droplet sizes between 10-100µm
Data-taking for 30h;re-pressureization for 10-15h
Two piezo-electric sensors on eachdetector
Data Analysis
Data with 3 detectors used for analysiswith an active mass of 7.45, 6.62 and5.35g
Total exposure was 1.98±0.19kg d
used local WIMP matter density of0.3GeV/c2/cm3, vrel=244km/s andvesc=600km/s (standard parameters)
Result
Count rate for 3 used detectors
Alpha rate of cleanest and older type ofdetector (with expected neutralino signalfor mWIMP=50GeV and =2pb, 5pb, 10pb)
Interpretation I
Exclusion plotfor spin-dependentneutralinos
lowest point inparameterspace
p=1.31pb andn=21.5pb for a
WIMP with29GeV mass
Interpretation II
Limits in spin-independent sector less stringent
Effective coupling strength an for neutrons and ap
for protons for a WIMP mass of 50GeV
7
Papers - in PressPublished by Phys. Lett. B 624, 3-4 (2005), 186-194
PICASSO 32 System
32 detectors
8 temperature and pressure control systems
up to 288 readout channels
sampling at 2MHz with 15.000samples/trigger
temperature stability 1/16ºC
operating range between 15º and 50ºC
switchable neutron source for calibration
Temperature and PressureControl System
Developed atQueen s
Houses 4 detectors
Operates between20 and 55ºC
Stable at 1/16 of adegree Celsius
all 8 are currently inproduction
PICASSO 324 new detectors are readyfor installation (sinceNovember)
-contamination belowsensitivity of surface lab
Purification method (withHTiO) now stable andreproduceable
New method has beenfound and is tested now
Exclusion Limit forPICASSO 32
Projected
The Area
8
Frame installation inFrame installation inJanuary at the sameJanuary at the samelocation as old setuplocation as old setup
Installation Schedule Data Taking
Future Plans SNOLAB
9
SNOLAB Plan SNOLAB Hopefuls
SNO+
Majorana (Majorana/Gerda III)
GasEXO
DEAP
SuperCDMS
PICASSO
Scaling of Picasso
Sketch for the 100kg active mass phase
Plan to move the system to the rectangular hallof SNOLAB
All of the details still have to worked out
Pending success in PICASSO 32 phase
Pending success in PICASSO 32 phase
Summary
Data taken in 2004 has been analyzed
PICASSO principle works
To be competitive background has to bereduced and system has to be scaled up
PICASSO 32 will be installed in the nextmonths
New, improved results to be ready nextyear