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Recent Progress in PICASSO

Sujeewa Kumaratunga for the PICASSO collaboration. Recent Progress in PICASSO. Outline. PICASSO Introduction Neutron Beam Calibration Data Analysis Results. SNOLAB. PICASSO. P roject I n CA nada to S earch for S upersymmetric O bjects or in French

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Recent Progress in PICASSO

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  1. Sujeewa Kumaratunga for the PICASSO collaboration Recent Progress in PICASSO Sujeewa Kumaratunga

  2. Sujeewa Kumaratunga Outline • PICASSO • Introduction • Neutron Beam Calibration • Data Analysis • Results

  3. SNOLAB 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. Sujeewa Kumaratunga

  4. Sujeewa Kumaratunga Spin-dependent Spin-independent Enhancement factor Neutralino Nucleon Interaction Crosssections General form of cross sections: CASI :Spin independent – coherent interactionA2 CASD : Spin dependent interaction<Sp,n>2 F(q2) : nucl. form facor  important for large q2 and large A

  5. How does PICASSO detect Neutralinos (WIMPs)? Sujeewa Kumaratunga

  6. Sujeewa Kumaratunga 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

  7. Sujeewa Kumaratunga Rmin Liquid Pvap Pext Pvap p = Superheat Pext Vapor « proto-bubble » Tb Top The Seitz Theory of Bubble Chambers • A bubble forms if: • particle creates a heat spike • with enough energy Emin • deposited within Rmin P(T) = superheat  (T) = Surface tension  = critical length factor  = energy convers. efficiency F. Seitz, Phys. Fluids I (1) (1958) 2

  8. 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 Sujeewa Kumaratunga

  9. 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 Sujeewa Kumaratunga

  10. Neutron Beam Calibration Sujeewa Kumaratunga

  11. Sujeewa Kumaratunga 50 keV Probability of detection Theory => detector efficiency 40 keV 5 keV 97 keV 61 keV Temperature (C) Test Beam Calibration • 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

  12. Sujeewa Kumaratunga Detection efficiency (T)‏ Neutralino response (T)‏ Test Beam Calibration

  13. Sujeewa Kumaratunga 226Ra spike (200 μm Ø)‏ 226Ra spike (200 μm Ø)‏ 226Ra spike (200 μm Ø)‏ 226Ra spike (200 μm Ø)‏ 226Ra spike (200 μm Ø)‏ Recoil nuclei from 50 GeV/c2 WIMP Recoil nuclei from 50 GeV/c2 WIMP Recoil nuclei from 50 GeV/c2 WIMP Recoil nuclei from 50 GeV/c2 WIMP Recoil nuclei from 50 GeV/c2 WIMP γ & MIP response γ & MIP response AmBe neutrons (data + Monte Carlo )‏ γ & MIP response AmBe neutrons (data + Monte Carlo )‏ γ & MIP response AmBe neutrons (data + Monte Carlo )‏ γ & MIP response AmBe neutrons (data + Monte Carlo )‏ AmBe neutrons (data + Monte Carlo )‏ PICASSO detector responses 226Ra spike (200 μm Ø)‏ Recoil nuclei from 50 GeV/c2 WIMP γ & MIP response AmBe neutrons (data + Monte Carlo )‏

  14. PICASSO Data Analysis Sujeewa Kumaratunga

  15. high pass filtered signal raw signal different amplitude scales neutrons noise PICASSO events Take power of signal and integrate to get energy : PVar Sujeewa Kumaratunga

  16. Sujeewa Kumaratunga PVar Distributions for Calibration Runs Distributions are temperature dependant

  17. Sujeewa Kumaratunga neutrons alphas PVar Distributions for neutron and alpha background Neutrons and alphas well separated signal

  18. Sujeewa Kumaratunga FVar Distributions for neutron and background Neutrons (WIMPs) & alphas Noise Blast Fracture

  19. Sujeewa Kumaratunga Null HypothesisAlpha Rate Fitted: Detectors 71,72 71 72 • Rates have been normalized to 19F

  20. PICASSO New Results Sujeewa Kumaratunga

  21. 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 Sujeewa Kumaratunga

  22. Sujeewa Kumaratunga 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

  23. backup Sujeewa Kumaratunga

  24. Sujeewa Kumaratunga • 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 • 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  - CDM ? • 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

  25. Sujeewa Kumaratunga Only 5% of matter is “visible” 22% of “invisible” universe => Dark Matter Dark Matter - Introduction • What is visible matter? • Baryons and radiation (things that interact electromagnetically)‏ • 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

  26. Sujeewa Kumaratunga Superheated Liquids For Particle Detection - timeline 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 & Dark Matter: SIMPLE, COUPP, PICASSO

  27. 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)‏ Sujeewa Kumaratunga

  28. Target selection Lithium (7Li)‏ Previous measurements: 7Li target 200 keV < En < 5000 keV. Vanadium (51V)‏ 528 keV 40 keV New measurements: 51V target 5 keV < En < 90 KeV Sujeewa Kumaratunga

  29. neutrons alphas 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! Sujeewa Kumaratunga

  30. Detector 71 Detector 72 Run length (days)‏ 101.5 103.5 Active Mass F19 per detetctor (g)‏ 65.06±3.2 68.97 ±3.5 Exposure (kg.d)‏ 6.60 7.14 Total Number of Events selected with Pvar ,Fvar 1721 632 Some numbers… Sujeewa Kumaratunga

  31. Systematics Systematic Uncertainty Active mass (C4F10)‏ 5% Neutron Threshold Energy 3% Pressure variation 3% Hydrostatic pressure gradient inside detector 2% Energy resolution 20% Temperature 0.1C Sujeewa Kumaratunga

  32. Sujeewa Kumaratunga 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!!

  33. 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 Sujeewa Kumaratunga

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