WIMP dark matter : direct detection 2013-12-10¢  WIMP signal in direct detection...

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Transcript of WIMP dark matter : direct detection 2013-12-10¢  WIMP signal in direct detection...

  • WIMP dark matter : direct detection

    Eric Armengaud (CEA Saclay - IRFU/SPP) Workshop «News from the dark» - Montpellier - 06/12/2013

  • • Principles of WIMP direct detection

    • History of the detection techniques and sensitivities

    • Focus on current sensitivity of XENON100/LUX for «standard» WIMPs

    • Other channels

    Refs : - L. Baudis review talk, SUSY 2013 - Particle Data Group review...

  • WIMPs : appealing and testable

    3

    χ

    χ

    q

    q

    Direct detection - observe the interaction of galactic WIMPs directly on a terrestrial detector - dedicated experiments, require a strong detector R&D + underground infrastructure

    Indirect detection - observe WIMP annihilation products from astrophysical objects - many « observatories » involved - current strongest constraint from FERMI : m ≳ 10 GeV for standard WIMPs

    Colliders - WIMP production, detection of some « missing energy »; monojet/photon events - a main goal of LHC, now that the SM is complete - if new particle discovered : does not prove that it is dark matter

  • Direct proof of WIMP dark matter: direct detection

    Interaction in a terrestrial detector

    Galactic WIMP velocity v ~ 200 km/s local density ρ0 Energy deposition

    Nuclear recoil Er

    θr

    Er = mχ 2 v 2

    #

    $ %

    &

    ' ( ×

    4mNmχ mN + mχ( )

    2 × cos 2ϑ r ~ 1 - 100 keV

    R ~ ρ0σ v mχ mN

    ~ 0.04 100 A

    %

    & '

    (

    ) * 100GeV mχ

    %

    & ' '

    (

    ) * *

    σ 0 10−8 pb %

    & '

    (

    ) *

    ρ0 0.3GeV cm−3 %

    & '

    (

    ) *

    v0 230 km s−1 %

    & '

    (

    ) * kg−1day−1

    Low-threshold detectors (~ few keV) Ultra-low-background detectors

    4

    • Scaling with MWIMP : low recoil energies at low MWIMP

  • WIMP signal in direct detection

    • Nuclear recoil spectrum ~ exponential • Scaling with A : ~ A2 for spin-

    independant (SI) coupling

    • Directionnality of recoils (~100% modulation)

    • Annual modulation 7% effect €

    dR dEr

    = σ 0 ρ0 2mχmr

    2 F 2(q) dv f1(v)

    vvmin

    Standard assumptions are used by expts to provide a reasonable comparison between sensitivities ⇒ put constraints in the plane (MWIMP,σ0) Systematics : - ⍴0~0.3 (0.0 - 0.8) GeV/cm3 - f1(v) : may include non-maxwellian velocity structures, additional dark disk etc. - nuclear + hadronic physics parameters !!

    New EW physics + hadron physics

    Nuclear physics

    Astrophysics (WIMP velocity distribution and local density)

  • WIMP signal in direct detection

  • WIMP detection is hard : signal vs backgrounds

    WIMP signal • Nuclear recoils • Single scatters in the detector • Interactions uniformly distributed in

    the detector volume • Exponential recoil spectrum • «A2» dependance • Annual modulation • Directionality

    Backgrounds • External gammas • Internal gamma contamination • Beta radioactivity : internal and

    surface • Alpha radioactivity • Neutrons from material radioactivity • Neutrons from cosmic muons • Neutrino (coherent) scattering

    Massive target (kg … ton[s] ) Low detection threshold ( ~ few keV) Background rejection :

    passive rejection = underground detector, shields, vetos.. active rejection = smart detector design

  • A wonderful playground for detector R&D

    BPRS

    ANAIS

    NaIAD

    DAMA

    KIMSLIBRA

    IGEX HDMS

    TEXONO

    CoGeNT

    C4

    CDMS EDELWEISS

    CRESST

    EDELWEISS-II

    CDMS-II

    ROSEBUD

    SuperCDMS EURECA

    GeoDM SIMPLE

    PICASSO

    COUPP

    PICO

    DRIFT DM-TPC

    MiMac

    DAMIC

    EDELWEISS-III

    ZEPLIN

    ZEPLIN-II

    ZEPLIN-III XENON-10

    XENON-100

    LUXXENON1t LZ

    DARWIN XMASS

    WaRP

    ArDM

    CLEAN DEAP

    DarkSide

    DEAP3600

    Panda-X CDEX

    Newage

    DM-Ice

  • • Principles of WIMP direct detection

    • History of the detection techniques and sensitivities

    • Focus on current sensitivity of XENON100/LUX for «standard» WIMPs

    • Other channels

  • History of sensitivities

    Oroville expt Phys. Rev. Lett. 61, 510 - 513

    • Germanium detectors (ionization) • Measure low-energy background spectrum down to ~ few keV • No background discrimination (ERs) • Compare to expected WIMP signal

    •NRs : take into account quenching factor signal(ENR) = Q x signal(EER)

    • Ancestors of CoGeNT

    ER scale

    Cosmogenic activation lines

    Compton plateau + surface radioactivity

    expt threshold ~ 3 keV sensitivity close to threshold

    depends more on details

    W IM

    P- G

    e

    nWIMP = ⍴/M

  • History of sensitivities

    DAMA limit 1996, Phys. Lett. B389, 757

    • Low-threshold scintillating crystals (NaI, CsI...) • Goal exploit pulse shape discrimination to reduce the ER background

    • Statistical discrimination only, and hard at low energy • Can reduce the bg intensity by factor ~ 1-10.

    • DAMA : then turned to annual modulation search (without PSD)

  • History of sensitivities • Low-temperature bolometers • Combine phonon (heat) with ionization or scintillation measurement

    • Event by event discrimination of ERs vs NRs • Orders of magnitude improvement in sensitivity

    EDELWEISS-II neutron calibration

  • History of sensitivities • Dual-phase Xenon TPCs • XENON10 - XENON100 - LUX - XENON1t • Discriminate ERs vs NRs with scintillation + ionization measurement

    • Not as splendid as in bolometers, but decent enough, especially and remarkably at low E

    • Scale to large volume (self-shieding) + radiopurity of Xenon : very low intrinsic bg • By far the leading technology as of 2013

    LUX - spatial distribution of background

    XE NO

    N1 00

    (2 01

    1)

    XE NO

    N1 00

    (2 01

    2)

    LUX (2013)

  • • Principles of WIMP direct detection

    • History of the detection techniques and sensitivities

    • Focus on current sensitivity of XENON100/LUX for «standard» WIMPs

    • Other channels

  • Dual-phase Xenon TPC

    « S1 » = direct light, scintillation « S2 » = light emitted when electrons are accelerated in the gas phase, ionization

    Discrimination between ER and NR Strong self-shielding

  • ER vs NR in practice for Xenon

    • Discrimination works even at low energy! BUT event populations overlap • Cut on Δlog(S2/S1) to reject most ERs

    ⇒ typical rejection power > 99% for an efficiency loss 50%

    First generation: Xenon10, ZEPLIN

  • Low-energy calibration of Xenon

    Scintillation signal :

    Ionization signal :

    Example of Leff measurement Plante et al., arXiv:1104.2587

    Neutron diffusion expt Scan over θ ! recoil energy Fit data to low-energy MC

    90% trigger efficiency

  • XENON100 : global fit of NR response AmBe calibration compared to (MC+absolute source flux measurement)

    arxiv:1304.1427

  • XENON100 WIMP search

    • z position : from electron drift time • r position : from PMT signal pattern

    - first «long run» : ~ 100 live days, fiducial Kr bckgd start to be limiting - reduced Kr → new run : 224 live days with expected bg ~ 1 event - Fiducial volume in the TPC : 34 kg (self-shielding against external radioactivity - PMTs ...) - « 2 events » : may belong to single electron tail ?

  • XENON100 results

    Limit derived from likelihood analysis Low-mass sensitivity may be disputed

  • LUX : first WIMP search

    • Run Apr-Jul 2013 @ Sanford lab, 4300 mwe

    • 370 kg LXe TPC (118 kg fiducial), 2x61 PMTs, very similar to Xenon • Drift field ~180V/cm • Light yield ~ 8 phe/keV ⇒better

    low energy response than XENON100

    • Remarkable low-energy ER «calibration»

  • LUX results

    85 live days - Neutron bg ~ 0.06 evt - ER bg in fiducial volume 3.1x10-3 evts/ kgd/keV

    in particular only 4ppt 85Kr 99.6% ER discrimination in 50% NR band : 0.6 evt

    - Analysis window [2-30] photoelectrons - Likelihood analysis based on S1,S2 and position

    Does NOT include «astrophysical uncertainties, nor calibration uncertainties (use NEST model)

  • Example of COUPP (but also PICASSO, SIMPLE) • CF3I chamber with cameras + piezo-acoustic sensors • Thermodynamical parameters well choosen: see NR above a given threshold, don’t measure a spectrum ! • Alpha bckgd : rejected with acoustic signal (alpha «louder» than NR) • COUPP-4 also has bckgd correlated with activity at the water/CF3I boundary

    - Mostly competitive for SD, but project to compete on the SI channel - COUPP-4 (4kg) done - COUPP-60 : under installation at SNOlab - Ton-scale projected (PICASSO joining)

    COUPP-60

    Other techniques