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Search for Dark Matter with Liquid Argon and Pulse Shape Discrimination

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Search for Dark Matter with Liquid Argon and Pulse Shape Discrimination Search for Dark Matter with Liquid Argon and Pulse Shape Discrimination Results from DEAP-1 and Status of DEAP-3600 Pierre Gorel for the DEAP collaboration! University of Alberta Dark matter! Experiment using liquid! Argon and ! Pulse shape discrimination Single phase WIMP detector ! (Scintillation signal & Pulse Shape Discrimination)! ! ! 3 ton-year background-free data ! (in Region of Interest) -46 2 Expected Sensitivity: σp=10 cm @Mχ= 100 GeV "2 Argon scintillation (PSD) Ionizing particle on Ar -> Dimer production! ∗ ! Ar2 → 2Ar + hν (128nm) Two states: Singlet and Triplet! ❖ Different time constant! ❖ Populated depending on Linear Energy Transfer Ionizing Singlet Triplet particle (~7ns) (~1.6#s) Electron 33% 67% Nucleus 75% 25% —>WIMP Signal "3 The prototype: DEAP-1 7kg 5 versions (2007-2011): Background & PSD "4 DEAP-1: what did we learn ? ❖ PSD strongly depending on Light Collection! P-A Amaudruz et al. (submitted to Astroparticle Physics) ! ❖ Good understanding of:! • Background in ROI: PSD leakage & Surface # ! • 222 Radon control: Rn ~16 $Bq/kg arXiv:1211.0909v2! 220Rn ~2 $Bq/kg (submitted to Astroparticle Physics) 3 ton-years background-free possible$ from extrapolation on measured PSD "5 Vale$ DEAP-3600$ Mine! Creighton Mine #9 Shaft MiniCLEAN! Airlock! ! Clean room (Class 2000) ! ! ! PICO! DEAP-1$ Damic! ! HALO! ! PICASSO! Machine Shop! COUPP Chemistry lab! Car wash! SNO+ Change rooms/Showers! Lunch room! Chiller/air filters! 2073 m Underground (6010 mwe) => 0.23 muon/m2/day A day at SNOLAB: http://www.youtube.com/watch?v=sZPLcv-ASwc! "6 "6 SNOLAB Virtual Tour: https://www.snolab.ca/facility/vr-tour Maximum light collection DEAP-3600: Background mitigation • 3600 kg of Liquid Argon! • 1000 kg Fiducial mass$ ! • 255 8”Photomultipliers! • Hamamatsu R5912, HQE! • 75% Coverage! ! • Spherical acrylic vessel ! • Cast from distilled monomer! • Inner 1mm layer removed after construction! ! • Neutron shielding against (#,n) in PMT glass! • Light guides (acrylic)! • Filler blocks (polyethylene+styrofoam)! ! • ∅7m x 7m ultra-pure water tank! • Shield against rock radioactivity! • Muon Veto (48 PMTs) "7 Construction status DAQ Rn scrubbers$ Purification systems Glove box N2 Dewar and Cryocoolers Water tank & Steel shell Acrylic vessel Filler blocks $ ! ! ! Specular reflectors$ ! Diffuse reflectors Ar Dewar "8 C. Strege et al, JCAP04 (2013) 013 Commissioning: Summer 2014$ Physics data: Fall 2014$ Leading sensitivity: 2 months of data "9 "10 Backup slides "11 DEAP-1: PSD Electric signal from PMT: Photon-electron counting: N FPrompt = prompt Nprompt + NLate Neutron (AmBe) γ(22Na) threshold Prompt : 0-150ns Late: 150ns-10µs "12 DEAP-1: PSD performance Leakage %/& into ROI (DEAP-1, measured) Leakage %/& into ROI with improved Light Collection WIMP WIMP 2.8PE/keVee! 43 keVee-86keVee 8PE/keVee! 15 keVee-30keVee Increased light Collection! => Better PSD / Lower threshold P-A Amaudruz et al. (submitted to Astroparticle Physics) DEAP-1: Background High energy spectrum, fitted with Radon daughters Low energy spectrum in ROI: Low energy cut off + improved PSD! =>NO # background in WIMP window arXiv:1211.0909 (submitted to Astroparticle Physics) AV construction September 2011$ April 2012$ October 2012$ Panel cast Panels bounding CNC machining January 2013$ Neck and shoulder July 2013$ February 2014$ bonding Light guides bonding Cleaning "15 Resurfacer ❖ Mechanical removal: 1mm acrylic! ! ❖ Flush with Ultra-Pure Water! ❖ Rn-scrubbed N2 cover gas! ! => Contamination level to bulk purity! (<10-19g/g of 210Pb) "16 DEAP-3600: Background budget Background Rate/Count Mitigation Shielding (6000 mwe, active water! Neutron! < 2 pBq/kg shield Light guides and filler block)! in 1t LAr < 0.06 count/year Material selection! %/&! < 2 pBq/kg Pulse Shape Discrimination! in 1t LAr < 0.06 count/year Material selection Material selection! Radon! < 1.4 nBq/kg SAES getter! in 1t LAr < 44 count/year Cold charcoal radon trap Material selection! Surface #! < 0.2 mBq/m Resurfacing! in 1t LAr < 0.6 count/year Fiducialization Total: <0.6 events in ROI in 3 years of data taking "17 Neutron background in DEAP-3600 # of neutrons Events in (In 3 years) (produced) ROI ! Acrylic vessel <44 (Ge &-assay) <0.096 ! ! Light guides <127 (Ge &-assay) <0.015 255 PMTs! Filler blocks <173 (Ge &-assay) <0.034 ! Light guides! PMTs 2.6x10 0.140 ! PMT mounts 7565 0. 010 Filler blocks! ! Rn emanation <44 <0.081 Acrylic vessel! Rn deposition ! ! 38 0.010 (3 months ! Otherconstruction) sources 0.04 Total <2.7x10 <0.35 "18 Calibration program Calibration Tools Optical Energy Radius$ Detector Response Reconstruction Reconstruction response and stability vs time LED, lasers, in-situ single PE tails ✔ ✔ ✔ Gamma sources (tagged ✔ ✔ ✔ 137 Neutron sources! (DD generator, ✔ ✔ ✔ AmBe) In-situ radioactivity! (39 ✔ ✔ ✔ ✔ gammas).
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