DEAP Dark Matter Experiment with Argon PSD Mark

DEAP: Dark Matter Experiment with Argon PSD Mark Boulay Queen’s University arxiv. org: /astro-ph/0402007 Mark Boulay DEAP 29/9/05

Outline: • Dark Matter Problem • Current techniques for direct detection of dark matter • Direct detection with Liquid Argon (LAr) • Some advantages of LAr • Design of and Results from DEAP-0: 1 kg LAr cryostat at LANL (preliminary results) • Plans for DEAP-1: 10 kg LAr cryostat at Queen’s (SNOLab early space) Mark Boulay DEAP 29/9/05

The Dark Matter Problem • Rotation curves – Mass density distributed more broadly than visible objects – Non-luminous halo required to describe rotation curves -First reported in 1933 by Zwicky Mark Boulay DEAP 29/9/05

Precision WMAP measurements map. gsfc. nasa. gov • Host of precision measurements culminating in WMAP. – Interpret power spectrum data by fit to cosmology DARK MATTER PROBLEM is > 70 years old and – Cold dark matter fraction experimentally sound : do not understand origin of accurately determined large fraction of matter in universe. Mark Boulay DEAP 29/9/05

Enter Supersymmetry… (…or a new type of particle makes up the dark matter…) • SUSY provides a “natural extension” to the standard model of particle physics • “Attractive route towards unifying all four forces ” -theorists • Introduces a new symmetry (R-parity) and possible existence of a new stable particle • New particle properties could well be consistent with those needed to account for the missing dark matter • Generically, direct searches are looking for WIMPs, Weakly Interacting Massive Particles, which would make up the dark matter • So SUSY provides a particle physics solution to a cosmological problem (SUSY not motivated by DM problem) Mark Boulay DEAP 29/9/05

Direct WIMP detection in terrestrial experiment • WIMPs can elastically scatter in detector producing nuclear recoils 40 Ar c • Rate in terrestrial detector depends on WIMP mass and WIMPnucleon interaction cross-section • Energy spectrum of recoils is exponential with E ~ 50 ke. V • Experimental challenge is to detect small number of nuclear recoils with low energy threshold (order event/1000 kg/year > 10 ke. V) Mark Boulay DEAP 29/9/05

The problem with direct WIMP detection (…or why these experiments are so tough…) • Radioactive decays from materials, and cosmic rays and their byproducts, are backgrounds to recoiling nucleus signal • Even clean materials can lead to billions decays/year for kg-scale detectors. Background events can be further divided into two classes: 1. Events that will ‘look like’ nuclear recoils 2. Events that won’t ‘look like’ nuclear recoils Mark Boulay DEAP 29/9/05

Backgrounds in WIMP searches In general, this roughly approximates to: 1. Neutron related backgrounds (since n’s can elastically scatter the target nuclei just like WIMPs can) 2. b/g radiation. This will deposit energy in a detector but not scatter the target nuclei. The approach taken is to reduce: 1. by using very clean materials and running experiment underground 2. by using clean materials and distinguishing n. r. events from b/g s Principle difference between DM experiments is how the distinction of n. r. events from b/g events is accomplished Mark Boulay DEAP 29/9/05

ASIDE: a-emitters plated out on detector surfaces as potentially dangerous background LAr Cryostat wall a 210 Po Decay in bulk LAr tagged by a-particle scintillation on surface Decay from surface releases untagged recoiling nucleus a Mark Boulay DEAP 29/9/05

CDMS (Cryogenic Dark Matter Search) Collection of small detectors simultaneously measure deposited energy in charge and phonon channels ~1 kg / “tower” g rays Exploits difference in deposited charge versus phonon energy between b/g ‘s and nuclear recoils Current best limit neutrons ZIP detector 250 g Ge Image from cdms. berkeley. edu Mark Boulay DEAP 29/9/05

XENON (proposed experiment) Many (most) DM experiments are technically very complex in order to discriminate b/g ‘s from nuclear recoils 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 Mark Boulay DEAP 29/9/05

DEAP (Dark Matter Experiment with Argon PSD) • Spin-independent WIMP-nucleon scattering on liquid 40 Ar • Spherical volume of LAr instrumented with PMTs to detect scintillation photons • Discrimination of g/b backgrounds using only scintillation time information from PMTs • Generic spherical design scaleable to large target mass DEAP-n: n = log 10(target mass [kg]) Mark Boulay DEAP 29/9/05

Scintillation in liquid argon • ionizing radiation leads to formation of excited dimers in argon (Ar*2) • dimers are produced in either singlet or triplet excited states • decays to ground state have characteristic times, and can result in photon emission • ~ 2 ns for singlet state (prompt) • 1. 6 us for triplet state (delayed) • Fraction of dimers in singlet versus triplet state depends on ionization density along track, and thus on incident particle type Net effect is a difference in the photon emission versus time curve for g/b events and for nuclear recoils Mark Boulay DEAP 29/9/05

http: //arxiv. org/astro-ph/0411358 scintillation pulseshape analysis for discrimination of e- vs nuclear recoils -> no electron-drift DEAP : Dark-matter Experiment with Argon PSD Mark Boulay DEAP 29/9/05

Idea is to use scintillation photons only for discrimination in DEAP… …allows for simple detector design and possibly a more easily realizeable large-scale experiment Mark Boulay DEAP 29/9/05

Some advantages of LAr • Inexpensive : 10 kg = 25$ or Lar • Good light yield, 40000 photons/Me. V = good resolution • Used extensively, very large experiments underground • Easily accessible temperature (~85 K) • Same requirements as LN for cryogenic components • “Noble” noble gas • Liquid experiment can be continuously or periodically purified (advantage over crystals) • Allows simple, inexpensive, scalable design Mark Boulay DEAP 29/9/05

Simulation of discrimination in argon • 6 pe/ke. V for 75% coverage, with • 1500 Hz PMT noise • Backgrounds from Ham. R 9288 (approx. 70 m. Bq/PMT) • 5 ns PMT resolution • 20% photon detection efficiency • 100 ns trigger window sets T 0 • Fprompt = Prompt hits(100 ns)/Total hits(15 us) • ~2 kg Ar with 10 ke. Vee threshold (60 pe) Dominant backgrounds assuming proper shielding, depth, and clean construction. Mark Boulay DEAP 29/9/05

Background rejection with LAr (simulation) 108 From simulation, rejection > 108 @ 10 ke. V (>>!) simulated e-’s 100 simulated WIMPs Mark Boulay (Goal for Super. CDMS is 108) DEAP 29/9/05

DM Sensitivity with LAr with 1 -year exposure LAr with 10 ke. V (electron) threshold Mark Boulay DEAP 29/9/05

Direct detection prediction from SUSY NMSSM (Next-to-MSSM) Prediction from talk by David Cerdeno at SUSY 2005 (JHEP 12 (2004) 048) 10 -44 cm 2 (10 kg LAr) 10 -45 cm 2 (100 kg LAr) Maybe within our reach! Mark Boulay DEAP 29/9/05

DEAP-0 (1 kg) at LANL 40” • PMT in air outside of large vacuum chamber • ~1 kg LAr viewed by single 2” PMT • calibration with g’s, n’s (tagged 22 Na and Am. Be) • Demonstration of PSD • Test long term gain stability DEAP-0 Timeline: DEAP-0 Design: Jan 05 M. Boulay, A. Hime, L. Rodriguez (LANL) Order components: Feb 05 Supported by LANL LDRD, Rec’d all components: 05 with technical assistance. May and advice from: Assembly: June, Jul 05 Steve Lamoreaux, Dan Mc. Kinsey, Data run & analysis: Jul, Aug 05 James Nikkel, Seppo Pentilla, … (Analysis being completed) Mark Boulay DEAP 29/9/05

Gas Handling System for DEAP-0 SAES purifier, < 0. 1 ppb Mark Boulay DEAP 29/9/05

DEAP-0 construction at LANL • Conflat construction, Cu gaskets, “standard” components where possible to reduce cost • ~1 kg of liquid argon with 2” windows, viewed by 1 PMT in air Mark Boulay DEAP 29/9/05

DEAP-0 Construction at LANL Liquid nitrogen cooling, Ar gas in Cu coils Mark Boulay DEAP 29/9/05

DEAP-0 Mark Boulay DEAP 29/9/05

DEAP-0 in vacuum chamber Mark Boulay DEAP 29/9/05

DEAP-0 PMT setup at LANL PMT coupled to LAr through chamber window Source with Cs. I/PMT for gamma tag Vacuum chamber windows Mark Boulay Cs. I tag LAr PMT source DEAP 29/9/05

DEAP-0 windows (post-warm-up) Window to argon chamber …room for improvement! Mark Boulay DEAP 29/9/05

PMT pulses from LAr, in coincidence with g in Cs. I g-like neutron-like Mark Boulay DEAP 29/9/05

Triplet lifetime check Mark Boulay DEAP 29/9/05

Discrimination in liquid argon Na-22 runs 4 x 106 tagged g’s Mark Boulay Am. Be runs (neutron calibration) <pe/ke. V> = 0. 1 DEAP 29/9/05

Discrimination in liquid argon from DEAP-0 <pe> = 60 preliminary O(1 in 105) consistent with random coincidence with room neutrons (preliminary) <pe> = 60 corresponds to 10 ke. V with 75% coverage • Final analysis and systematics evaluation being done (Kevin and Reuble) Mark Boulay DEAP 29/9/05

Conceptual design of DEAP-1 • ~10 kg Lar • Spherical geometry • PMTs coupled to inner chamber through light guides • PMTs surrounded by polyethylene for n absorption • Inner chamber could be (stainless steel, acrylic, copper) • Investigate using expanded polystyrene for thermal insulation (vacuum chamber if needed) Mark Boulay DEAP 29/9/05

Photon detection for DEAP-1 Acrylic light guide (UVA) Low background PMT window or acrylic vessel LAr 85 K 6” 300 K Acrylic guide backs off PMT to reduce (a, n) neutron backgrounds, and to reduce thermal load. Q = k. A(Th-Tc)/L ~ 1 Watt Mark Boulay DEAP 29/9/05

Photomultiplier tube (PMT) backgrounds in DEAP-1 For reference, 250 events/year for the ET 9390 PMTs Mark Boulay DEAP 29/9/05

Inner cryostat backgrounds in DEAP-1 4 neutrons/year/kg of SS (Peter Skensved) ~3% leakage into signal region (Geant 4 Monte-Carlo) problematic background! • Investigating acrylic chamber for inner cryostat (Kevin Graham) • Could possibly use Copper cryostat Internal backgrounds (impurities in LAr) • Will use gas purification and cold charcoal traps • In-situ assay of internal backgrounds with DEAP-1 Mark Boulay DEAP 29/9/05

Neutron active veto (conceptual) Note: thermal neutron capture cross-section on Ar: 675 mbarn Active neutron veto LAr Vacuum region n • Active veto can mitigate internal and external low-energy (a, n) neutrons • Relaxes internal (a, n) requirements • Possible overlap with SNO+ for liquid scintillator active veto Mark Boulay DEAP 29/9/05

Optimizing optics for DEAP-1 elg epmt “Toy” optics model a Y 0 = 0. 8 = 0. 25 =0 = 40 photons/ke. V Model incorporating reflective losses and absorption: Y=R[1/S-1] elgepmt(1 -a)Y 0 Y = yield [photons/ke. V] R = surface reflectivity S = surface PMT coverage elg = light guiding efficiency epmt = PMT efficiency a = absorption Y 0 = photon production yield Mark Boulay Need real model to map inputs to yield, O(10%) (Kati N. ) DEAP 29/9/05

Short-term activities for DEAP-1 at Queen’s • Develop optical model for use in chamber and light guide design, test model in the lab: GEANT 4 simulation for optics Most parts ordered for light guide/reflectivity tests using a-scintillation in gaseous argon (~1 month to parts? ) • Design cryostat for proper cooling and background requirements for 10 kg detector and for optics/background tests with LAr • Inner chamber R&D (acrylic versus copper versus stainless) • Design and construction of clean room Once these are in place, design and build clean 10 kg experiment (DEAP-1) Mark Boulay DEAP 29/9/05

DEAP-1 Timeline and SNOLab • Currently designing cryostat, selecting components • Clean room being constructed at Queen’s • Plan is to construct and commission DEAP-1 at Queens O(6 months) • Calibration & verification of PSD above ground, spring/summer 2006 • Seek “early” SNOLab space Fall 2006 for UG running • 10 -44 cm 2 with one year livetime Funding for DEAP-1 is in place with CFI/startup grant from Queen’s and LANL LDRD support O(750 K total) • Philosophy is to design DEAP-1 so that scaling to DEAP-3 is feasible, x 100 improvement in background required Mark Boulay DEAP 29/9/05

Response of SNOLab Experiment Advisory Committee to DEAP: “Very interesting and recent technical developments using LAr provide the possibility for a conceptually simple and relatively inexpensive route to a large-scale detector. Given existing funds and plan to go forward, we strongly encourage submission of a technical proposal for DEAP-1. ” -SNOLab EAC recommendations, August 2005 meeting Mark Boulay DEAP 29/9/05

Conclusions • DEAP-0 (1 kg) succesfully executed at LANL • Demonstrated discrimination using PSD only in LAr • Currently designing DEAP-1 (10 kg) for construction at Queen’s • Possibly ready for deployment in early SNOLab space (Sept 2006) 10 -44 cm 2 sensitivity with 1 live-year, 10 ke. V threshold • Funding for DEAP-1 in place, CFI/startup + LANL LDRD Opportunity for hardware design, analysis, Monte-Carlo simulation, underground experiment deployment and running experience, and …potential Discovery of New Physics beyond the new Standard Model… on the timescale of a Ph. D Mark Boulay DEAP 29/9/05