searching for wimps underground the experimental quest
Download
Skip this Video
Download Presentation
SEARCHING FOR WIMPS UNDERGROUND: THE EXPERIMENTAL QUEST

Loading in 2 Seconds...

play fullscreen
1 / 30

SEARCHING FOR WIMPS UNDERGROUND: THE EXPERIMENTAL QUEST - PowerPoint PPT Presentation


  • 63 Views
  • Uploaded on

SEARCHING FOR WIMPS UNDERGROUND: THE EXPERIMENTAL QUEST. Henrique Araújo Imperial College London IOP2011 NPPD CONFERENCE 3-7 April 2011, University of Glasgow. Outline. WIMP scattering signal The experimental challenge Recent results Great expectations. What are we looking for?.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' SEARCHING FOR WIMPS UNDERGROUND: THE EXPERIMENTAL QUEST' - donar


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
searching for wimps underground the experimental quest

SEARCHING FOR WIMPS UNDERGROUND:THE EXPERIMENTAL QUEST

Henrique Araújo

Imperial College London

IOP2011 NPPD CONFERENCE

3-7 April 2011, University of Glasgow

outline
Outline
  • WIMP scattering signal
  • The experimental challenge
  • Recent results
  • Great expectations

H. Araújo

what are we looking for
What are we looking for?

WIMPs attract most experimental effort

A neutralino LSP would make a great WIMP

WIMPs should scatter off ordinary nuclei

producing measurable nuclear recoils

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

interactions (neutral current exchange)

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

signal calibration
Signal calibration

Ge (CDMS-II)

Xe (X100)

  • 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 sources

H. Araújo

elastic scattering rates
Elastic scattering rates

Canonical model (‘we’re all in it 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

1. Spin-independent (scalar) interaction

    • note A2 in enhancement factor
    • cMSSM-favoured XS within reach of current detectors

2. 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

Probably

just around the corner

by end 2011

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 kTfiducial mass (self-shielding)

  • But doing both is hard!

Small is better for collecting signal

Large is better for background

  • And there is no trigger…

H. Araújo

backgrounds
Backgrounds
  • Nuclear recoils – same signature
    • Radioactivity neutrons: (a,n) and SF from U/Thcontamination
      • 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-nucleus 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

slide11

ionisation

Q

L

scintillation

H

phonons

Discrimination

Ionisation Detectors

Targets: Ge, Si, CS2, CdTe

CoGeNT, DRIFT, GENIUS,

HDMS, IGEX, NEWAGE

Light & Ionisation Detectors

Targets: Xe, Ar

ArDM, LUX, WARP,

XENON, ZEPLIN

cold (LN2)

Heat & Ionisation Bolometers

Targets: Ge,Si

CDMS, EDELWEISS

cryogenic (<50 mK)

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

Light & Heat Bolometers

Targets: CaWO4, BGO, Al2O3

CRESST, ROSEBUD

cryogenic (<50 mK)

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

self shielding in noble liquids

LUX  LUX-ZEPLIN 1.5t

Neutrons (5-25 keV)

Gammas (5-25 keV)

Self-shielding in noble liquids

Liquid

xenon

r=3 g/cm3

Sacrificial

volume

neutron

gamma

Fiducial

volume

S2

S1

S2

S2

H. Araújo

S2

anticoincidence detector around wimp target

LUX  LUX-ZEPLIN 1.5t

Neutrons (5-25 keV)

Gammas (5-25 keV)

Anticoincidence detectoraround WIMP target

veto

Liquid

Xenon

make

thin!

neutron

gamma

Water cherenkov, passive LXe, bare or loaded scintillator,…

H. Araújo

anticoincidence detector around wimp target1
Anticoincidence detectoraround WIMP target

Akimov et al, arXiv:1103.0393

  • A veto buys you:
  • Background reduction
    • Up to order of magnitude for gammas and neutrons
  • Diagnostic power
    • Unexpected backgrounds
    • Radiation environment
  • Signal-free background sample
    • Calculation of background expectations without compromising blind analysis

Effect of veto efficiency

on the discovery power

of a rare event search

with a single background

and no additional

discrimination

NT is the number of tagged events observed

H. Araújo

dama libra scintillation
DAMA/LIBRA: Scintillation

GRAN SASSO

Target: 250 kg NaI(Tl)

8.9s CL modulation

over 13 annual cycles

Barnabeiet al, arXiv:1002.1028

(Something is modulated, but what?)

H. Araújo

anais scintillation
ANAIS: Scintillation

CANFRANC

Target: aiming for 250 kg NaI(Tl)

With 500 kg.years data, the DAMA result could be reproduced if threshold ~2 keVee and background <2 evt/kg/day/keV

ANAIS STATUS

XXXIX IMFP CANFRANC 10-FEB-2011

Carlos Pobes

- Various prototypes developed over last decade

- Excessive K-40 contamination in existing crystals - Radio-pure detectors under development

- Mass production from end 2011

Anais-0 being tested at old LSC

Ready to be installed in new LSC facilities

H. Araújo

edelweiss ii ionisation phonons

 S. Henry tomorrow

EDELWEISS-IIIonisation & Phonons

MODANE

Target: 4 kg Ge

384 kg·days from 14 months of operation 5 candidate events above 20 keV

estimated background is <3.0 events

sSI<4.4×10−8pb (90% CL) at 85 GeV

E. Armengaudet al, arXiv:1103:4070v2

H. Araújo

cresst scintillation phonons
CRESST: Scintillation & Phonons

GRAN SASSO

Target: 3 kg CaWO4

Observed 57 events (yes, fifty seven!)

in 730 kg*days in oxygen band

Background prediction 35.6 events

(of which 17.3 from neutrons, measured from only 3 multiple scatters)

J. Schmaler (German Physical Society meeting, 30 Mar 2011)

H. Araújo

light wimps excesses at low energies
Light WIMPs: ‘excesses’ at low energies

DAMA

CoGeNT

CRESST

A ‘glimmer’ or a ‘flicker’?

Phys. Rev. 26, 71–85 (1925)

CMSSM Buchmueller et al

CMSSM Trotta et al

Aalseth et al, arXiv:1002:4703v2)

H. Araújo

what would zeplin iii make of it
What would ZEPLIN-III make of it?

You cannot

be serious!

13 GeV WIMP AT sSI=3x10-5pb

Z3 FIRST RUN OBSERVATION: 7 events near top of acceptance region in 2-16 keVee

Recoil spectrum in xenon

140 kg*days in FSR signal box

30 events >2 keVee!

H. Araújo

coupp bubble chamber
COUPP: Bubble chamber

SNOLAB

Target: 3.5 kg CF3I

E. Behnke et al, PRL 106, 021303 (2011)

Run at shallow site (Fermilab): 3 candidate events were observed in 28.1 kg.days, consistent with neutron background.

Electron recoils do not nucleate bubbles

Background from neutrons and alphas

Ultrasound emission provides powerful discrimination between alphas and nuclear recoils (as demonstrated by PICASSO)

H. Araújo

zeplin iii scintillation ionisation

 wed pm parallel session

ZEPLIN-III: Scintillation & Ionisation

BOULBY

Target: 12 kg LXe, 6.5 kg fiducial

>280 days continuous operation

Result from ~2,000 kg*days soon

Sensitivity 1-2x10-8pb

CMSSM Buchmueller et al

CMSSM Trotta et al

H. Araújo

slide27

XENON100: PLR analysis

Target: 62 kg liquid xenon, 30 kg fiducial

E. Aprile,

XIV Int. Workshop on Neutrino Telescopes,

Venice, 16 Mar 2011

H. Araújo

slide28

XENON100: “result in weeks”

Target: 62 kg liquid xenon, 30 kg fiducial

E. Aprile,

XIV Int. Workshop on Neutrino Telescopes,

Venice, 16 Mar 2011

“ ‘unblinding procedure’ in final stage of internal review

‘Blind’ analysis of ~10x

more data near completion

Results expected within weeks. Non negligible discovery potential”

H. Araújo

the future
The future

GEN-1

ANAIS

ARDM

COGENT

COUPP

CRESST

DAMA

DARKSIDE

DM-TPC

DRIFT

EDELWEISS

KIMS

LUX350

MiniCLEAN

NEWAGE

PICASSO

SCDMS

WARP

XENON100

XMASS

ZEPLIN-III

GEN-2

DARKSIDE

DEAP-3600

EURECA

LZS

PICASSO-II

SCDMS

XENON1t

XMASS-II

GEN-3

COUPP

GEODM

LZ20

MAX

CLEAN

H. Araújo

conclusions
Conclusions

Dark matter is one of the hottest topics in science today

The field of underground WIMP searches is very vibrant,

attracting strong investment worldwide (mustn’t grumble…)

Direct, indirect and accelerator searches are finally converging in sensitivity for neutralino-proton interactions

An exciting 2011: new results expected from Gen-1 targets and significant design/construction activity at tonne scale

H. Araújo

ad