October 8th, 2009 Sujeewa Kumaratunga 1/27 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 P roject I n CA nada to S earch for S upersymmetric O bjects or in French P rojet d' I dentification de CA ndidats S upersymétriques SO mbres 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 C A SD : Spin dependent interaction  2 F(q 2 ) : nucl. form facor  important for large q 2 and large A Neutralino Nucleon Interaction Crosssections Enhancement factor General form of cross sections: C A SI : Spin independent – coherent interaction  A 2 Spin-dependentSpin-independent

October 8th, 2009 Sujeewa Kumaratunga 5/27 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 E min deposited within R min The Seitz Theory of Bubble Chambers R min P ext P vap « proto-bubble »  P(T) = superheat  (T) = Surface tension  = critical length factor  = energy convers. efficiency F. Seitz, Phys. Fluids I (1) (1958) 2 T op P vap Liquid TbTb P ext Vapor  p = Superheat

October 8th, 2009 Sujeewa Kumaratunga 8/22 PICASSO detectors Super heated C 4 F 10 droplets  200μm,  held in matrix in polymerized gel  act as individual bubble chambers When neutron interactions cause 19 F recoils or ionizing particle deposits energy  Superheated liquid vaporizes forming small bubbles  Bubbles grow explosively (50μs)  Turns entire C 4 F 10 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 g  g of Freon mass  Temperature & Pressure control system 40 hr data taking 15hr recompression

October 8th, 2009 Sujeewa Kumaratunga 10/27 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 7 Li and 51 V 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 keV Probability of detection 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 226 Ra spike (200 μm Ø)‏ AmBe neutrons (data + Monte Carlo )‏ Recoil nuclei from 50 GeV/c 2 WIMP γ & MIP response 226 Ra spike (200 μm Ø)‏ AmBe neutrons (data + Monte Carlo )‏ Recoil nuclei from 50 GeV/c 2 WIMP γ & MIP response 226 Ra spike (200 μm Ø)‏ AmBe neutrons (data + Monte Carlo )‏ Recoil nuclei from 50 GeV/c 2 WIMP γ & MIP response 226 Ra spike (200 μm Ø)‏ AmBe neutrons (data + Monte Carlo )‏ Recoil nuclei from 50 GeV/c 2 WIMP γ & MIP response 226 Ra spike (200 μm Ø)‏ AmBe neutrons (data + Monte Carlo )‏ Recoil nuclei from 50 GeV/c 2 WIMP γ & MIP response 226 Ra spike (200 μm Ø)‏ AmBe neutrons (data + Monte Carlo )‏ Recoil nuclei from 50 GeV/c 2 WIMP γ & MIP response

October 8th, 2009 Sujeewa Kumaratunga 14/27 PICASSO Data Analysis

October 8th, 2009 Sujeewa Kumaratunga 15/22 PICASSO events raw signal high 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 neutrons alphas 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 Hypothesis Alpha Rate Fitted: Detectors 71,72 Rates have been normalized to 19 F 72 71

October 8th, 2009 Sujeewa Kumaratunga 20/27 PICASSO New Results

October 8th, 2009 Sujeewa Kumaratunga 21/22 PICASSO New Results σp = pb ± 0.124pb ± 0.007pb (1σ) 90%C.L. limit of σp = 0.16 pb for a WIMP mass of 24 GeV/c ±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 kg 32 det expected sensitivty 0.05 pb

October 8th, 2009 Sujeewa Kumaratunga 23/27 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/ 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 = pb ± 0.124pb ± 0.007pb (1σ) limit of σp = 0.16 pb (90%C.L.) for a WIMP mass of 24 GeV/c ±0.48 kg.days  (Previous exposure 1.98 kg days)‏

October 8th, 2009 Sujeewa Kumaratunga 28/22 Lithium ( 7 Li)‏ Vanadium ( 51 V)‏ 528 keV 40 keV Previous measurements: 7 Li target 200 keV < E n < 5000 keV. New measurements: 51 V target 5 keV < E n < 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! neutronsalphas

October 8th, 2009 Sujeewa Kumaratunga 30/22 Some numbers… Total Number of Events selected with Pvar,Fvar Exposure (kg.d)‏ ± ±3.2Active Mass F 19 per detetctor (g)‏ Run 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 (C 4 F 10 )‏ UncertaintySystematic

October 8th, 2009 Sujeewa Kumaratunga 32/22 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 = pb ± 0.124pb ± 0.007pb (1σ) 90%C.L. limit of σp = 0.16 pb for a WIMP mass of 24 GeV/c ±0.48 kg.days