The DEAP Experiment Dark Matter Experiment with Argon PSD Kevin Graham Queen’s University M. Boulay, M. Chen, K. Graham, A. Hallin, J. Lidgard, R. Matthew, A.B. McDonald, K. Nicolics, P. Skensved Case Western Reserve University M. Dragowsky Los Alamos National Laboratory Hime, D. Mei, K. Rielage, L. Stonehill, J. Wouters SNOLAB F. Duncan, I. Lawson Yale University D. McKinsey, J. Nikkel

Evidence for Dark Matter lensing gmeasure lens mass from multiply imaged arcs measure velocities of galaxies in cluster measure velocity of gas/stars vs radius from galactic centre v2c = G M(r) / r if light traces mass v should fall at large radii…but does not HST Abell 2218 85% of matter is dark matter! Mihos NGC 2403

Direct Detection of Dark Matter Cold Dark Matter a WIMPS (can also be LSP!) predict at the earth: dark matter energy density 0.3 GeV/cm3 Sun orbiting at 220 km/s for a given mass and interaction cross-section estimate c-n scattering rate /kg/year/keV direct measurement: look for: elastic scattering of WIMPs in detector producing nuclear recoils a low energy and falling 10-100 keV ause LAr with PSD DM signal or improve limit on scattering cross-section (expect 10’s of events/year) c 40Ar

Detection in LAr ionizing radiation forms dimers in LAr dimers produced in singlet(I1) or triplet(I3) state singlet state decay time much shorter than triplet intensity of singlet and triplet states depends on ionization density along track and hence particle type ns

g-like neutron-like

DEAP0 at LANL (Boulay and Hime) Setup Goals ~1 kg LAr viewed by single 2” PMT CsI counter used for tag calibration with tagged g’s, n’s 22Na: back-to-back 511 keV g’s AmBe: n and 4.4 MeV g demonstrate pulse shape discrimination determine b/g suppression level (expect O(108) from MC simulation) measure I1/I3 for g’s and neutrons PMT LAr CsI tag Vacuum chamber windows source Digitized Pulse Total Charge

Deap0 Calibration 22Na 511 keV g AmBe neutron a ~0.1 PE/keV PromptPE = integral in 250 ns TotalPE = integral to 10 ms FPrompt=PromptPE/TotalPE expect ~0.3 for b/g ~0.8 for n determine charge/single PE know peak for 22Na is 511 keV a ~0.1 PE/keV (sets sensitivity) 22Na 511 keV g AmBe neutron 22Na 511 keV g

Preliminary Results 22Na AmBe determine fraction of 22Na above 0.7 for 55-65 PE suppression O(105) consistent with background limits neutrons in region above 0.7 uncorrected b/g and neutron I1/I3 22Na AmBe use background data to determine real and accidental coincidence rate

DEAP1 ~10 kg of liquid argon view with 2 - 5” PMT’s use clean materials and shielding in construction calibrate detector response at Queen’s move to SNOLAB early in 2007 measure b/g suppression down to 10 keV threshold position reconstruction in “z” at SNOLAB understand background rates/types can already be competitive within a few months exposure! prepare for 1 tonne experiment

Neck connects to vacuum and Gas/liquid lines Quartz windows 11” x 6” Stainless steel tee 6” acrylic guide Acrylic vacuum chamber PMT 5” inner surface 97% diffuse reflector, covered with TPB wavelength shifter

DEAP1 Constructed! first LAr fill 2 weeks ago response looks good! begin calibrating next week

Backgrounds Type Sources Rate Suppression Method b/g a’s R&D in U/Th/K 39Ar 106 events/year clean materials PSD (108) clean Ar? a’s recoils ionizing R&D in progress position recon. PSD neutron thermal fast(a,n) muon induced 4000 /m2/day <0.27 /m2/day shielding SNOLAB depth

DM Sensitivity with LAr with 1-year exposure LAr with 10 keV (electron) threshold DEAP1

Summary initial proof-of-principle PSD (complete) calibration of DEAP1 at Queen’s (first fill so far) aPE/keV, reconstruction, b/n response at 10 keV calibrate and understand backgrounds at depth if bkg controlled competitive DM limits soon! begin design of DEAP3 (1 tonne) experiment!

LAr Cryostat wall Decay in bulk detector tagged by a-particle energy 210Po on surface Decay in bulk detector tagged by a-particle energy Decay from surface releases untagged recoiling nucleus Cryostat wall LAr a Fig 6: Alpha emitters deposited on the detector surface are a potentially dangerous background.

Radon Contamination minimize exposure clean/etch surfaces 210Po on surface Decay in bulk detector tagged by a-particle energy Decay from surface releases untagged recoiling nucleus Cryostat wall LAr a minimize exposure clean/etch surfaces reconstruction suppression

Dewar Schematic liquefy purified Argon gas and maintain at 85o K vacuum chamber argon line liquid nitrogen at ~30 PSI getter

CDMS (Cryogenic Dark Matter Search) g rays Exploits difference in deposited charge versus phonon energy between b/g ‘s and nuclear recoils Collection of small detectors simultaneously measure deposited energy in charge and phonon channels ~1 kg / “tower” Current best limit neutrons (Currently instrumented 5 kg mass) ZIP detector 250 g Ge Image from cdms.berkeley.edu

Backgrounds CDMS Collab Meeting 15 Oct 2005

Direct detection prediction from SUSY NMSSM (Next-to-MSSM) Prediction from talk by David Cerdeno at SUSY 2005 (JHEP 12 (2004) 048) 10-44 cm2 (10 kg LAr) 10-45 cm2 (100 kg LAr) maybe within our reach!

SNOLAB Excavation Status DEAP Collab Mtg 10 May 2006

Evidence for Dark Matter clustering of galaxies (LSS) sensitive to amount of DM angular power spectrum of CMB sensitive to baryonic, DM, DE Virgo Consortium Add breakdown of matter content here

For almost as long as WIMPs have been around (if they DO exist!)… U, Th chains are present in all materials with 109, 1010 y lifetimes ~104decays/kg/year for ppt (1 in 10-12) impurities Removing backgrounds to WIMP particle interactions is the task of DM searchers

CDMS (Cryogenic Dark Matter Search) g rays Exploits difference in deposited charge versus phonon energy between b/g ‘s and nuclear recoils Collection of small detectors simultaneously measure deposited energy in charge and phonon channels ~1 kg / “tower” Current best limit neutrons (Currently instrumented 5 kg mass) ZIP detector 250 g Ge Image from cdms.berkeley.edu

XENON (proposed experiment) Total Xe mass 1 tonne Exploits difference in ionization signal (electrons) versus scintillation signal (photons) between b/g‘s and nuclear recoils Figure from Elena Aprile Dark Matter 2004

Background rejection with LAr (simulation) From simulation, rejection > 108 @ 10 keV (>>!) 108 simulated e-’s 100 simulated WIMPs

Triplet lifetime check

Photomultiplier tube (PMT) backgrounds in DEAP-1 For reference, 250 events/year for the ET9390 PMTs

Optimizing optics for DEAP-1 elg = 0.8 epmt = 0.25 a = 0 Y0 = 40 photons/keV Model incorporating reflective losses and absorption: Y=R[1/S-1] elgepmt(1-a)Y0 Y = yield [photons/keV] R = surface reflectivity S = surface PMT coverage elg = light guiding efficiency epmt = PMT efficiency a = absorption Y0 = photon production yield Need real model to map inputs to yield, O(10%) (Kati N.)

Dark Matter Candidates Baryonic Dark Matter - MACHOs - Brown Dwarfs Hot Dark Matter - neutrinos Non-Standard Gravity - MOND Cold Dark Matter - Axions - WIMPs - R-parity conserving supersymmetric models predict stable LSP (typically neutralino c) - can have ‘right’ properties for cold dark matter!

Evidence for Dark Matter angular power spectrum of CMB sensitive to baryons, DM, DE 85% of matter is dark matter! neutrinos ~few % of matter WMAP Three Year Results

Summary using SNOLAB facility and based on the experience and success of SNO, there is a unique opportunity for Canadians to lead experimental research in - direct search for dark matter - low-energy solar neutrinos - neutrinoless double beta decay SNO+ will have access to most interesting physics for low-energy solar neutrinos and experiment is built! DEAP can rapidly evolve from concept to leading edge dark matter experiment – simple, inexpensive, scalable!

Backgrounds expect DM small signal /keV/tonne/day background suppression crucial non-nuclear recoil events PSD nuclear recoil events (shielding, reconstruction) clean clean clean clean clean!