The PICASSO Dark Matter Search Experiment:

1. The PICASSO Dark Matter Search Experiment: Tony Noble Queen’s University • The PICASSO Detector Technique • Overview of Phased approach to PICASSO in SNOLab • Current Status • Recent R&D Progress • Significant R&D issues to be resolved. • Anticipated Infrastructure requirements. • Personnel SNOLab Workshop #4

2. PICASSO • Superheated Droplet Detector • Detector consists of tiny (5 to 100 m) halocarbon liquid droplets (C3F8, C4F10...) embedded in a gel. • The droplets are superheated - maintained at a temperature higher than their boiling point. SNOLab Workshop #4

3. Picasso • WIMP induced nuclear recoils deposit a spike of heat into droplet. This causes droplet to evaporate rapidly. • The evaporating bubble creates a sound shock wave, which can be recorded by a sensitive piezo-electric microphone. • ~ Insensitive to β, γ, radiation, and other MIPS • Low Threshold. ~ 5 to 10 keV En SNOLab Workshop #4

4. Advantages of this Technique • Favorable spin-dependent neutralino cross section on 19F • Good connection to industry as small versions are used for n-dosimetry (BTI-Chalk River and Apfal). • Droplets superheated at ambient T & P • Threshold as low as En = 5 to 10 keV • Insensitive to ,  and cosmic  radiation at operational T & P Probe of the Spin Dependent Sector SNOLab Workshop #4

5. Overview of Run Plan • Phase 1: • Small prototype detectors (1 L). Have been running with these in SNO. First Results just published: Proof of principles demonstrated • Upgrading to larger detectors (4.5 L). 100 x Increase in active mass. Larger droplet size. • Phase 2: • Development of larger detectors. (30 L) • Improved purification • Develop New Gel • Phase 3: • Full scale PICASSO detector. • Improved purification SNOLab Workshop #4

6. PICASSO PHASES Rough outline of scheduled phases Estimated limits. Detailed calculations in progress with MC simulations SNOLab Workshop #4

7. Current Status SNOLab Workshop #4

8. PIC@SNO • Operational since fall ’02 • Rn –free facility • remote control from Montréal • 6 detectors, 2 piezos/det. SNOLab Workshop #4

9. PICASSO Results. • Recently Published • Proof in principle demonstrated. • Competitive with worlds best with ~2 Kgd Physics Paper: Physics Letters B. hep-ex/0502028. Technical Paper: Submitted to NIM. physics/0508098 SNOLab Workshop #4

10. Lessons Learned • Long term operation of complete underground experiment • Remote operation • Development of complete set of tools for analysis • Successful implementation of DAQ, slow-control… • First order purification successful • (technique adapted from SNO by • M. Di Marco in PhD work) • Published first results. Early detector: Partial purification. Later Detector: More complete purification. SNOLab Workshop #4

11. Recent R&D Progress SNOLab Workshop #4

12. The next detectors: • Currently under testing and construction • 32 detectors, each 4.5 l volume • 9 Piezo detectors each Photoshop image of array of 32 SNOLab Workshop #4

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14. Radio-purification: • Main source is α from U and Th in CsCl gel …. ~ 10-9 gU/g • Application of HTiO ion exchange technique adapted to CsCl and other ingredients has helped a lot. (Order factor of 20 reduction) done “by hand” on lab bench. • Now have clean rooms in Montreal and Queen’s. • Have built purification plant which allows large batches to be purified and assayed with multiple passes. • We are investigating the use of HZrO as a better agent for CsCl. • Tests on-going. SNOLab Workshop #4

15. Raw Salt Measured U As built detectors II, U Purified salt. U Raw Salt Measured Th Th Criteria U Criteria SNOLab Workshop #4

16. Radio-purification: • Will soon reach limit with CsCl gel and this technique. A further order of magnitude reduction should be easily possible with new plant, but eventually we will reach limit from Cs activity itself. • Gained factor of 6 to 8 reduction with new fabrication method and larger droplet size. • We are also working on the development of a much cleaner gel. • BTI have successfully made gels based on Ethylene Glycol / Glycerin mixtures. • Apfal make a similar proprietary material. • Queen’s has made a scintillating gel that shows some promise. (this would be the ideal solution, as then one has an active veto for α induced activity in the gel, and a direct measure of this background.)… Early days yet. These gels are intrinsically much cleaner. Studies are ongoing to understand how suitable they are for long lived bubble detector applications. SNOLab Workshop #4

17. Temperature and Pressure Control System: • Need to maintain temperature uniform and stable to within factor of ~0.1 C over a range of ~15 to 55 C • New temperature control system developed at Queen’s is now ready for use. Double walled thermally insulated box. Resistive heating on top and bottom plates PID block tuned to keep temperature stable and uniform. SNOLab Workshop #4

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20. Temperature and Pressure Control System: • Need to be able to “reset” the detectors by compressing at ~120 psi for ~10 hours. (Normal operation is at ambient pressure.) This puts bubbles back into superheated liquid droplet phase. • In last run, we determined a source of background events came from N2 gas dissolved in the gel. This gas would come out of solution when decompressed, producing acoustic triggers. This was the result of using radon free N2 gas as the pneumatic compression agent. • We have developed a new system which uses clean mineral oil to compress the gel hydraulically. • Other Improvements: • - Event Localization algorithms. (Queen’s & UdeM). Using GPS like stratagies the acoustic signals from 9 piezo detectors can be used to localize events. Preliminary tests and MC simulations are suggestive of a vertex resolution of < 1cm. • New DAQ system. (Montreal) • New Piezo sensor design.(IUSB) • Detector Container fabrication. (Prague) SNOLab Workshop #4

21. Main Technical Issues • Radio-purity of the gel material. • New expertise in group with ethylene-glycol/glycerine matrix. Being tested for radio-purity • New Research Scientist / Radio-chemist, Started in June at Queen’s. • Some hope for a scintillating gel, but compatibility with Freon to be determined. • With PICASSO, SIMPLE, BTI, Yale/Apfal we have ~ the worlds • expertise on developing these types of detectors • Development of Purification Plant • Development of 30 l detectors and polymerization • Increasing loading: Active mass per detector • (most recent tests show factor 2 improvement. Very promising) SNOLab Workshop #4

22. Resources and Infrastructure Needs: Phase 3 Rough ideas only at this stage! • Space: • 6m x 7m x 10m (LxWxH) when assembled • 13m x 7m x 10m (LxWxH) during access + Chilled air supply. + UPW for shielding + ~50 kW power for heating + Radon free cover gas + SNOLab Workshop #4

23. Manpower in Current Phase of PICASSO Université de Montreal: V. Zacek prof. 100%PICASSO ( project leader) L. Lessard prof. 100% PICASSO container development, test beam calibration C. Leroy prof. 25% PICASSO, ass. Director LADD, Monte Carlo simulations, analysis G. Azuelos prof. 25% PICASSO, Monte Carlo J.-P. Martin res. physicist 25% PICASSO all electronics and DAQ devel., 75% LADD U. Wichoski RA (physicist+ engineer), data analysis, detector fabrication, organisation N.N. RA to be appointed F. Aubin MSc detector calibration, data filterng, neural net analysis M. Auger MSc starting fall ‘05 P. Doane PhD purification & detector favrication R. Gornea PhD data acquistion system, filtering algorithms, piezo sensor expert M. Bernabé-Heider MSc calibration, active mass determination, backgroud measurements M.H. Genest PhD Monte Carlo simulation, active mass determination R. Guénette MSc analysis, simulations S.S. x2 2 summer students, June –Sept. 05 Y. Landry technician fabrication preamps, read out boards, available as required N. Starinski engineer 40% PICASSO, 60% LAAD G. Richard technician head of machin shop, 50% PICASSO (MFA), more if required SNOLab Workshop #4

24. IUSB: E. Behnke: Undergraduate, 100%- active since start summer 2003, piezo preamp I. Levine: prof. phys. 2/3 Picasso 1/3 SNO various aspects of acoustics program W. Feighery: prof., chem. Pb loading in detectorsC. Muthusi Undergraduate, chemistry, Pb loading Queens University: A. Noble prof. 50% PICASSO local contact to SNO, purification issues, various aspects in R&D C. Krauss: RA 50% SNO / 50% PICASSO, DAQ X.X. Dai RA 50% SNO/SNO+ / 50% PICASSO, purification issues K. Clark PhD 100% PICASSO C. Storey M.Sc 100% PICASSO N.N Expect 1 new PhD and 1 new MSc in fall 05 S.S. 2 summer students ‘05 University of Pisa: S. Shore prof. 15% PICASSO, theoretical issues related to bubble formation and detector performance, general Dark Matter issues, interpretation of results SNOLab Workshop #4

25. Prague Technical University S. Pospisil Prof. 25% PICASSO, dir. fabrication detector modules I. Stekl Prof. 25% PICASSO, dir. fabrication detector modules, radon test J. Sodomka Prof. Fabrication detector modules J. Bocan PhD 100% PICASSO, Monte Carlo simulations Yale University F. d’Errico Prof. Detector fabrication, signal form analysis. Providing detectors at cost through Apfal BTI R. Noulty + Industrial Partners. Detector development and fabrication Partners for Full “Picasso” Project. MOU Signed Paris VI, VII G. Waysand Prof. 100% SIMPLE Dir. Rustrel underground lab; System. Detector studies D. Limagne engineer 100% SIMPLE detectctor fabrication Universita di Lisboa T. Girard Prof. Group leader SIMPLE F. Giuliani RA data analysis, interpretation simulations T. Morla t RA detectector fabrication J. G. Marques neutron irradiations A. Fernandes neutron irradiations, simulations R. Martins instrumentation M. Da Costa instrumentation SNOLab Workshop #4

26. Summary • PICASSO. Moving well towards full scale detector in SNOLab. Phased approach will ensure physics results emerge along with development. Major thrust is to develop radio-purity program. • PICASSO: Technique demonstrated. Physics results emerging. • PICASSO Manpower: • 8 to 10 FTE Faculty and Postdocs • 5 to 6 PhD students • 5 to 6 MSc students • ~6 Undergraduate students • PICASSO: Large fraction of the world’s expertise in Bubble detector development exists in collaboration, including connection with two industrial partners. • Will need ongoing funding support for operations, and an MFA for capital cost of full detector. SNOLab Workshop #4