An experimental overview of direct dark matter searches
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AN EXPERIMENTAL OVERVIEW OF Direct Dark Matter Searches. Henrique Araújo Imperial College London IOP2010 – JOINT HEPP/APP GROUP MEETING 29-31 March 2010, University College London. What are we looking for?. Scalar (SI) and axial-vector (SD) c -N interactions (neutral current exchange):.

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An experimental overview of direct dark matter searches

AN EXPERIMENTAL OVERVIEW OFDirect Dark Matter Searches

Henrique Araújo

Imperial College London

IOP2010 – JOINT HEPP/APP GROUP MEETING

29-31 March 2010, University College London


What are we looking for

What are we looking for?

  • Scalar (SI) and axial-vector (SD) c-N interactions

  • (neutral current exchange):

WIMPs attract most experimental effort,

but axion searches are a growth industry

I assume here that the Lightest SUSY Particle

is the neutralino, c, which is a great WIMP

WIMPs should scatter off ordinary nuclei

producing measurable nuclear recoils

But, essentially, WIMP searches are not really (PP-)model dependent…

H. Araújo


Low energy nuclear recoils

Low energy nuclear recoils

  • Elastic scatter off nucleus:

    • Decreasing, featureless spectrum of low-energy recoils (<~50 keV)

    • Rate depends on target mass & spin, WIMP mass & spin, DM halo, …

    • Neutrons are irreducible background

  • Inelastic scatter off nucleus:

    • Short-lived, low-lying excited states (easier signature?)

    • 129Xe(3/2+→1/2+) + g(40 keV), 73Ge(5/2+→9/2+) + g(13 keV)

    • Neutrons are irreducible background

  • Inelastic dark matter (iDM):

    • “particles will scatter at DAMA but not at CDMS” (Smith & Weiner 2001)

    • Recoil spectrum with threshold (mass splitting, d)

    • Neutrons are irreducible background

H. Araújo


Elastic scattering rates

Elastic scattering rates

Canonical model: not great, but we’re all in this together:

  • Isothermal sphere (no lumps), r∝ r−2

    • Local density r0~0.3 GeV/c2/cm3 (~1/pint at 100 GeV)

  • Maxwellian (gaussian) velocity distribution

    • Characteristic velocity v0=220 km/s,

    • Local escape velocity vesc=600 km/s

    • Earth velocity vE=232 km/s

  • H. Araújo


    Elastic scattering rates1

    Elastic scattering rates

    • Coupling to protons and neutrons more useful than coupling to nucleus

      • To compare different target materials, indirect searches, LHC results

    • Spin-independent (scalar) interaction

      • note A2 in enhancement factor

      • cMSSM-favoured XS within reach of current detectors

    • Spin-dependent (axial-vector) interaction

      • note J (nuclear spin) instead of A2 enhancement

      • cMSSM-favoured XS out of reach for the time being…

    H. Araújo


    Si scattering rates for 1 kg targets

    SI scattering rates for 1 kg targets

    H. Araújo


    The experimental challenge

    The experimental challenge

    • Low-energy particle detection is easy ;)

      E.g. Microcalorimetry with Superconducting TES

      Detection of keV particles/photons with eV FWHM!

    • Rare event searches are also easy ;)

      E.g. Super-Kamiokande contains 50 kT water

      Cut to ~20 kT fiducial mass (self-shielding)

    • But doing both is hard!

      Small is better for collecting signal

      Large is better for background

    • Ah: and there is no trigger…

    H. Araújo


    Building a wimp detector

    Consider 1 kg target

    Sensitive to Edep>1 keV

    Expected WIMP rates

    0.1−0.000001 evt/day

    However…

    Cosmic rays, a, b, g-rays

    >1,000,000 evt/day

    Neutrons are THE background!

    Several evt/day

    m

    b

    g

    n

    a

    Building a WIMP detector

    WIMP

    1 kg

    H. Araújo


    Building a wimp detector1

    Move underground

    Use radio-pure materials

    Shield external g-rays

    Shield external neutrons

    Actively veto neutrons

    Discriminate e-recoils (g, b) from n-recoils (WIMPs, n)

    Building a WIMP detector

    WIMP

    H. Araújo


    Nuclear recoils backgrounds

    Nuclear recoils - backgrounds

    • Nuclear recoils – same signature

      • Neutrons from (a,n) and SFissionfrom U/Th trace contamination

        • Laboratory walls, shields, vessels, components, target material

      • Neutrons from atmospheric muon spallation

        • Difficult to shield completely even underground

      • Recoils from alpha emitters (e.g. Rn-222 and progeny)

        • Contaminating active target bulk/surfaces, air, etc

      • Eventually, even coherent neutrino scattering

    • Electron recoils – discrimination power is limited

      • Gamma-ray background external to target

        • K-40, Cs-137, U/Th from walls, shields, vessels, components

      • Contamination of target bulk and surfaces

        • U/Th betas and gammas (Pb-214, Bi-214, Pb-210,…)

        • Cosmogenic (Ge-68, Ge-71,…), anthropogenic (Kr-85, Cs-137,…)

    H. Araújo


    Nuclear recoils signal acceptance

    laboratory system

    incoming

    neutron

    En

    q

    nuclear

    recoil

    ER

    En

    Nuclear recoils - signal acceptance

    Ge (CDMS-II)

    • 100 GeV WIMP on Xe (A=131):

    • 220 km/s WIMP → ER,max = 40 keV

    • 1 MeV neutron → ER,max = 30 keV

    • Neutron elastic scattering populates WIMP acceptance region

      • Calibration of detection efficiency with Am-Be (a,n), Cf-252 (SF), D-D, D-T

    • But there are complications:

      • Multi-element: in CaWO4 (CRESST), WIMPs couple mainly to heaviest material (W), but neutrons scatter mainly off lightest (O). Signal acceptance must be calibrated indirectly

      • Quenching factor: in noble liquids (ZEPLIN,XENON,WARP,ARDM,…) conversion from “electron-equivalent” to nuclear recoil energy is not straightforward (or favourable…)

      • Droplets: in C4F10 superheated droplets (SIMPLE,PICASSO) phase transition is independent of energy. Calibration of signal acceptance threshold only

    H. Araújo


    Discrimination single channels

    ionisation

    Q

    L

    scintillation

    H

    phonons

    Discrimination: single channels

    Ionisation Detectors

    Targets: Ge, Si, CS2, CdTe

    CoGeNT, DRIFT, GENIUS,

    HDMS, IGEX, NEWAGE

    Scintillators

    Targets: NaI, Xe, Ar

    ANAIS, CLEAN, DAMA,

    DEAP, KIMS, LIBRA,

    NAIAD, XMASS, ZEPLIN-I

    Bolometers

    Targets: Ge, Si, Al2O3, TeO2

    CRESST-I, CUORE, CUORICINO

    Bubbles & Droplets

    CF3Br, CF3I, C3F8, C4F10

    COUPP, PICASSO, SIMPLE

    H. Araújo


    An experimental overview of direct dark matter searches

    ionisation

    Q

    L

    scintillation

    H

    phonons

    Discrimination: hybrid detectors

    Heat & Ionisation Bolometers

    Targets: Ge,Si

    CDMS, EDELWEISS

    cryogenic (<50 mK)

    Light & Ionisation Detectors

    Targets: Xe, Ar

    ArDM, LUX, WARP,

    XENON, ZEPLIN

    cold (LN2)

    Light & Heat Bolometers

    Targets: CaWO4, BGO, Al2O3

    CRESST, ROSEBUD

    cryogenic (<50 mK)

    All 3 hybrid technologies

    > 99.9% discrimination

    @ >10 keV NR energy

    H. Araújo


    Phonons microcalorimetry

    Phonons (microcalorimetry)

    Cryogenic: T0~50 mK

    Thermal phonon signal is lost with increasing mass:

    must collect phonons before they thermalise in absorber

    • Superconducting Transition-Edge Sensor (as in CDMS)

    • Collect high-frequency (athermal) phonons from particle interaction

    • Into superconducting Al contacts (threshold 2DAl~ meV)

    • Quasiparticles from broken Cooper pairs diffuse into a W TES

    • SQUID readout offers extremely high sensitivity

    • Channel threshold: 1 keV for Ge & Si nuclear recoils

    J. Cooley, CDMS Collaboration

    H. Araújo


    Scintillation photomultipliers

    Scintillation (photomultipliers)

    DAMA/LIBRA Collaboration

    Room temperature, cold or cryogenic

    NaI, CsI, CaWO4, LXe, LAr: many materials scintillate…

    Photomultipliers: ancient vacuum tube technology,

    but no-one has come up with a better alternative yet

    (and we’re trying…)

    • Scintillation detectors (as in DAMA)

    • Best photomultipliers now approaching 50% quantum efficiency

    • Best NaI(Tl) crystals yield ~90 photons/keV for gamma rays

    • Typically require coincidence of two photomultipliers (2 phe)

    • Threshold: 0.3-3 keV for I nuclear recoils

    • (depending on “channelling” effect)

    H. Araújo


    Ionisation electroluminescence tes hemt jfet

    S2

    (electroluminescence)

    Ionisation(Electroluminescence, TES, HEMT, JFET)

    Cold: T0~200 K

    Difficult to measure one electron, but not so hard to measure electroluminescence photons from one electron

    • Two-phase xenon detectors (as in ZEPLIN)

    • Strong electric field across liquid-gas xenon target

    • Collect ionisation from particle track in liquid Xe

    • Drift up to surface, then emit into vapour phase

    • Electroluminescence photons detected with photomultipliers

    • Threshold: 0.2 keV for Xe nuclear recoils

    1e

    Edwards et al., Astroparticle Phys. 30 (2008) 54

    H. Araújo


    A few examples not comprehensive and somewhat uk centric

    A few examples(not comprehensive and somewhat UK-centric)

    H. Araújo


    Cresst scintillation phonons

    CRESST: Scintillation & Phonons

    Target: 0.6 kg CaWO4

    3 events observed in

    10-40 keVnr acceptance region

    48 kg·days exposure (2007)

    Angloher et al, Astropart. Phys. 31 (2009) 270

    H. Araújo


    Zeplin iii scintillation ionisation

    ZEPLIN-III: Scintillation & Ionisation

    Target: 12 kg LXe

    7 events observed in

    10-30 keVnr acceptance region

    850 kg·days raw exposure (2008)

    (likely e-recoil background)

    Lebedenko et al, PRD 80 (2009) 052010

    H. Araújo


    Cdms ii ionisation phonons

    CDMS-II: Ionisation & Phonons

    Target: 4.4 kg Ge, 1.1 kg Si

    2 events observed in

    10-100 keVnr acceptance region

    612 kg·days exposure (2007-08)

    Background estimate 0.8±0.2!

    Ahmed et al, arXiv:0912.3592

    H. Araújo

    J. Cooley, CDMS Collaboration


    Dama libra scintillation

    DAMA/LIBRA: Scintillation

    Target: 250 kg NaI(Tl)

    8.9s CL modulation

    over 13 annual cycles

    Barnabei et al, arXiv:1002.1028

    (But what is modulated?

    and is it getting smaller?)

    H. Araújo


    Drift ni gas tpc

    DRIFT – NI Gas TPC

    Target: 167 g/m3 CS2 (now CS2+CF4)

    Unlikely that backgrounds mimic signal which appears as forward/backward asymmetry in galactic coordinates

    H. Araújo


    Picasso superheated c 4 f 10

    PICASSO: Superheated C4F10

    Target: 65+69 g C4F10

    H. Araújo


    Cogent ionisation p type point contact ppc hpge

    CoGeNT - Ionisationp-type point contact (PPC) HPGe

    Target: 330 g Ge

    Excess at low energies – a glimmer?

    Aalseth et al, arXiv:1002:4703v2)

    No discrimination, too close to threshold…

    H. Araújo


    World status prospects si

    World status & prospects (SI)

    H. Araújo


    World status prospects sd

    World status & prospects (SD)

    H. Araújo


    World status prospects idm

    World status & prospects (iDM)

    Schmidt-Hoberg & Winkler, JCAP09(2009)010

    Akimov et al., arXiv:1003.5626 (ZEPLIN-III)

    H. Araújo


    Next generation a view

    Next generation: a view

    TWO-PHASE ARGON

    • A=40, <ER>= 13 keV @50 GeV/c2, 35 keV @500 GeV/c2

    • very scalable (cheap, large LAr systems demonstrated)

    • poor energy threshold, low atomic weight, Ar-39 background

    • WARP, ArDM, (DEAP/CLEAN) working on 0.1—1 tonne targets

    • 5-tonne system within 5 years is (optimistically) possible

      CRYOGENIC GERMANIUM

    • A=73, <ER>= 13 keV @50 GeV/c2, 57 keV @500 GeV/c2

    • excellent energy resolution, excellent discrimination

    • difficult to scale (small detector modules, <50 mK cryostats)

    • CDMS, EDELWEISS, (CRESST) working on 10—20 kg targets

    • EURECA and SuperCDMS propose ~100 kg target in 5 years

      TWO-PHASE XENON

    • A=131, <ER>= 11 keV @50 GeV/c2, 85 keV @500 GeV/c2

    • scalable, low threshold

    • control of xenon purity to <ppb is demanding

    • ZEPLIN-III, XENON100, LUX350, (XMASS), working on 10-100 kg

    • XENON1T and LUX-ZEPLIN propose 1 tonne two-phase xenon targets

    Proposals (>1 tonne)

    CDEX, CLEAN, COUPP+, DAMA+, DARKSIDE, DARWIN, DEAP3600, DRIFT, EURECA, GEODM, KIMS+, LUX-ZEPLIN, MAX, SuperCDMS, XMASS, …

    H. Araújo


    Next generation a view1

    Next generation: a view

    Araujo, Strigari & Trotta

    Araujo, Strigari & Trotta

    H. Araújo


    Ready to scale up

    Ready to scale up!

    Pack ?

    UK pioneered several search technologies

    NaIAD, ZEPLIN-I, DRIFT-I, CRESST-I, ZEPLIN-II, DRIFT-II, CRESST-II, ZEPLIN-III, ArDM, EDELWEISS, (EURECA, LZ)

    And pushed forward “underground science”

    Dating back to Holborn Station Laboratory…

    Creating the Boulby Underground Laboratory

    (see Sean Paling’s talk tomorrow)

    But we’re running out of road…

    H. Araújo


    Click to add funding

    Click to add funding

    Thank you


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