Search for with Liquid 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) (~1.6s) 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 α

• 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 /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 (α,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 β/γ into ROI (DEAP-1, measured) Leakage β/γ 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 α 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

β/γ < 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 α < 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 γ-assay) <0.096 ! ! Light guides <127 (Ge γ-assay) <0.015 255 PMTs Filler blocks <173 (Ge γ-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)