Status and Prospects for WIMP
Dark Matter Detection
Neil Spooner (University of Sheffield)
10-12pb
dream
detector
Higgs05
•
Dark Matter and WIMPs
•
Current search results
ionisation, scintillation
phonons, xenon, gas
•
Under construction
•
Towards 1, 10, 100 tonne
•
WIMP astronomy?
10-12pb
dream
directional
detector
Concordance of the Universe
Contributions to W
Total (100%) W0 =1
ThreeAll“dark”
problems
and
matter 27%
Non-baryonic
A dark exotic
dark matter
>95%
of
the
Universe
is
still
form of
Baryons 4%
baryonic
Energy?
unidentified
dark
matter
Stars 0.5%
73% still missing
Higgs05
>95% is Unidentified
something for an
experimentalist to do
also
theorists
!
Higgs05

Why WIMPs and Neutralinos
COSMOLOGY
There should be CDM - non-relativistic, no interactions with photons
collapse of density fluctuations start early
There should be Non Baryonic DM
Wm (LSS, CMBR, SN) ~ 7 x Wb (BBN, CMBR)
CMB alone requires non baryonic dark matter:
WMAP+... Wmh2 = 0.14 ± 0.02 >> Wbh2 = 0.024 ± 0.024 ± 0.001
anyway how do you hide the baryons?
PARTICLES IN THERMAL EQUILIBRIUM
Freeze out when annihilation rate ≈ expansion rate
27
3
2
2
3
3
10
cm
/s

M
T
W h 2 =
  A  2 ,   EW
 Av
M EW
M pl
So cosmology indicates generic WIMPs at W&Z scale
PARTICLE PHYSICS
Standard model requires new physics at W&Z scale - supersymmetry - neutralino
BUT not only supersymmetry - e.g. Extra Dimensions - G. Servant et al.
Higgs05
Particle Candidates - a big space?
ADMX
yuk!
thanks to L. Roszkowski
Higgs05
Lightest Kaluza-Klein Particle
Worth looking at other WIMP candidates
Alternative (or supplement) is Extra Dimension theory
Stable Kaluza-Klein modes of ordinary standard model particles allowed
to propagate in one or more compact extra dimensions
LKP (Lightest Particle)
Applies as generic
Bosonic Dark
Matter candidate
LSP Neutralino - Majorana (self-annihilate) fermions (spin 1/2), R-parity
LKP interacts with SM particles and is stable because of KK parity
• 5d theory gives all properties for a well-motivated WIMP candidate
• Mild assumptions, not many parameters needed to describe LKP (unlike neutralino)
• Detection possible by direct and indirect means
Many papers now, e.g.:
Servant et al. ANL-HEP-PR-02-054, ANL-HEP-PR-02-032,Cheng CERN-TH/2002-157
Higgs05
Cross sections for LKP
SD and SI WIMP(KK)-Nucleon cross sections vs. WIMP mass
Servant et
• Assumes a Higgs mass of 120 GeV
al.
• Higher Higgs mass lowers the cross section (x10 for 300 GeV)
• Greater B(1), q(1) degeneracy increases cross section
Typical values KK
10
spin
6
 scalar
~
10
pb
______

~
10
pb
p,n
p,n
12
6
spin
9
6
Typical values neutralinos  scalar
~
10
10
pb
____

~
10
10
pb
p,n
p,n
Higgs05

Signals Decline? - MACHOs
Neural network analysis
(Evans et al.)
END of the MACHO ERA
“...the microlensing towards the LMC or
Andromeda provide little if any evidence
for any MACHO component in galaxy
halos” - Evans et al. IDM2004
• MACHOs have had their day
fhalo dm ~20% and likely to fall
• M31, LMC experiments
little if any evidence of MACHOs
• Could be other baryonic material
-hydrogen flakes
-supermassive black holes
Higgs05
6 probably microlensing events
2 likely microlensing events
2 contaminations (Seyfert or variable star)
1 event looks perfect but known by EROS
to repeat
Neutralino - MSSM
Broad region if GUT
constraints lifted
With grand unified theories
allowed region collapses
focus
point
Narrow allowed bands from
WMAP (Wh2) + collider + GUT
Experimentalists
conclusion:
worth a bet!
100
mC(GeV)
1000
L. Roszkowski et al.
Higgs05
WIMP Search Strategy
Accelerator searches
SuperK result
Indirect Searches
AMANDA, ICECUBE, ANTARES, KM3,
CANGARO, MAGIC, HESS, Veritas, AMS,
GLAST, SuperK, EGRET, WMAP
Direct Searches
WIMP
total event rate
(point like nucleus)
dR = Ro e -ER/Eor
dE R
Eor
incident
energy
kinematic factor
= 4MDMT/(MD + MT)2
dR =R S(E) F2(E) I(A)
o
dE
obs
(Eor/Ro)*dR(vE,vesc)/dER
Complementary to direct searches (spin dependent) but more
model dependent and less sensitive for low mass, low 
10
9
8
7
6
5
4
3
2
1
0
featureless differential
nuclear recoil energy
spectrum
0 1 2 3 4 5 6 7 8 9 10
E/(E0r)
so need nuclear recoil discrimination, low background, go underground
Higgs05
Direct Detection Techniques
~20 years work
finding techniques
to reject gamma Ge
background
Ge, Si
heat
ionisation
BGO,
CaWO4
WIMP
Xe
light
movement
gas (CS2)
discrimination: none, statistical, event by event
Higgs05
LiF,
Al2O3
NaI, CsI,
Xe
Signal, what signal?
• technology
scintillators
semiconductors
s/c grains
ion-thermal
xenon
directional/gas
point 2
two targets/detectors is good
Higgs05
point 1
must have gamma rejection
solved (>105), because neutrons
will become main problem
point 3
a directional signal is good
show that events are galactic
Germanium - ionisation only
Ge probably best purity, but no recoil discrimination Main Efforts on Background
IGEX
2.1 kg Ge (2)
0.21 ev/kg/d/keV
benchmark sensitivity: ~8 x 10-6 pb
scale-ups --> GEDEON
Heidelberg-Moscow
28-56 Kg
2.3 kg Ge (2
aim for 0.01
ev/kg/d/keV
0.05 ev/kg/d/keV
scale-ups --> Genius-TF
Higgs05
35 Kg
Genius
Ionisation-thermal (2003/4)
Edelweiss-I
• Oct 02-Mar 03 - New exposure
13.8 kg.days >20 keV.
• See some events - keep 2 and
set limit.
Neutron Calibration
3 x 320 g
(ionisation
+heat) Ge
Data: 3 months
Gammas
Neutrons
benchmark sensitivity: 1.4 x 10-6 pb
Higgs05
Ionisation-thermal (2003/4)
CDMS-II
• first Soudan runs
Recent world best result
WIMP data for Z2,3,5
with same cuts
ionisation yield calibration
with 252Cf on Z2,3,5
Tower 1
Previously
1/2 year run
@ Stanford
90% cl Benchmark limit at 60 Gev
2
spin-independent: 4 x 10-7 pb
• low field with segmented contacts to allow rejection of near edge events
• collect athermal phonons - ZIP technology
• xy positioning and pulse shape analysis
Higgs05
Liquid Xenon - single phase
ZEPLIN-I (UKDM)
• Single phase lq. Xe; 5 kg (3.2 kg fiducial)
• Discrimination by pulse shape time constant ratio (TC)
• three 8cm, 9265Q PMTs
• 4 cm Xe turrets
• 30 cm liquid scintillator veto
• 1.5-2.5 p.e./keV
• E(rms)/E0.5 = 1.19 +/- 0.02
Benchmark limit ~ 1.1 x 10-6 pb
example
of adding recoils for TC=0.5
major
advance
in
xenon
Gammas
tagged Am/Be 20-30 keV, TC=0.64+/- 0.04
Neutrons
Calibration
example for
7-10 keV
Data
Higgs05
NaI - DAMA (annual modulation)
DAMA - NaI
• 100 kg of NaI(Tl) at Gran Sasso - 107,731 kg.d
• Annual modulation analysis (no pulse shape analysis since ‘96)
• 7 annual cycles analysed
claimed evidence
of WIMP detection
MC = 52 +10-8 GeV
C-N= (7.2 +0.4-0.9) x 10-6pb
Higgs05
Current status (SI) - ~10-6pb (2003/4)
(UKDM)
ZEPLIN I-Lq Xe
Edelweiss I-Ge
CRESST II-CaWO4
IGEX-Ge
(UKDM)
NAIAD - NaI
CDMS II-Ge/Si
How can this be compatible with
CDMS, EDELWEISS and ZEPLIN I,
which do not see WIMPs…..?
DAMA - NaI
assumes standard halo but see e.g. Copi+Krauss astr-ph/0307185
Higgs05
Possibility 1 - wiggle room? e.g:
Many different model assumption explored - can push allowed region around
Model uncertainties
Halo structure - v0, vesc
Form factors (Helm) (I, Ge, Xe…)
Quenching factors
Possible conclusion:
Non-SUSY candidates
“ DAMA can still be explained by
SI, SD, mixed models, inelastic
a WIMP with spin dependent
(see K.Freese et al.
couplings but at masses too low
astro-ph/0309279)
SD contribution
for MSSM”
• if pure SI probably no wiggle room
(e.g. Savage - IDM2004)
could push
• but SD solution also difficult
region down
a steep spectrum but SD would give flatter spectrum
- I and Na comparable (no A2 dominance) need to look at influence of this on the other new limits
Higgs05
PLB-480(2000)23
keV Residuals
2-3 0.54 +/- 0.09
3-4 0.21+/- 0.05
4-5 0.08+/-0.02
5-6 0.03+/-0.01
WHAT’S NEXT
(path of no detection)
10-7-10-8pb (2005/6)
10-8-10-10pb
event rates
(2008/11)
in construction
needs 1 tonne
100 events in 1 tonne, 90% cl --> ~ 10-9 pb
need to achieve backgrounds <10-100 ev/yr
10-12pb (2015)
needs 100 tonnes
(~zero background)
WIMP physics at lowest cross sections
Higgs05
How?
(~zero background)
can it be
done?
neutrons are critical
U, Th
rock
Rock neutrons
rule of thumb: rock gamma rate = 106 x neutron rate
once  discrimination ~x105-6 then
neutrons are the main concern
detectors are already
close to this
evts
disc
Muon neutrons
Detector neutrons
Higgs05
In construction - 10-7-10-8pb (2005/6)
Edelweiss II
100 lt cryostat for up to
120 detectors (36 kg Ge)
(21 x 320 g) 2004
LIBRA - NaI
CRESST
(DAMA)
(250 kg-annual modulation)
Scale-up to
10 kg planned
ZEPLIN II and III
CDMS II
more towers
(4.5 kg Ge, 1.2 kg Si)
(UKDM)
two-phase
xenon
(6-30 kg)
Higgs05
Apologies for those techniques and groups left out...
Xenon Basics
Xe+
Ionisation
(1) Single Phase Experiments
DAMA Xe
ZEPLIN I (PSD)
XMASS I (no PSD)
+Xe
Electron/nuclear recoil
Xe2+
Excitation
+e(recombination)
Xe*
(2) Double Phase
Xe** + Xe
should give necessary
105-6  rejection?
+Xe
175nm
ZELIN
II
Triplet
27ns
Xe2*
175nm
Singlet
3ns
Xe gas
electroluminescence (2nd pulse)
ionisation
Lq Xe
primary (1st pulse)
scintillation

2Xe
2Xe
XMASS II
XENON 10,100
ZEPLIN II, ZEPLIN III
Higgs05
Xe - two phase - under construction
ZEPLIN-II 30 kg design based on scale-up
of UCLA 1 kg
test chamber
UKDMC + UCLA, Texas A&M, ITEP
Higgs05
ZEPLIN-III
6 kg high
field
Towards 1 Tonne Detectors
Main Issues
•
gamma rejection solved?, neutron reduction?, scaleable?, reasonable cost?
Possibilities
•
GENIUS (HDMS) proposal for 100kg --> 1 tonne ?
Intrinsic low background but NO discrimination and expensive (mainly bb)
•
LIBRA (DAMA) 250 kg now running
Annual modulation (what if DAMA region ruled out), PSD not sensitive enough
•
Cryo-array (“SDMS”, Edelweiss) ideas for 1 tonne
Good discrimination but difficult technology and expensive
•
ZEPLIN-MAX/IV proposal for 1 tonne
Good discrimination, simpler but less proven technology?, less expensive?
•
XMASS 1 tonne (needs 10 tonnes) ?
Intrinsic low background but NO discrimination and expensive (mainly bb)
Higgs05
Are neutrons ok at 1 tonne?
neutron simulations for Large Scale Xenon
M. J. Carson et al. Astrop. Phys. 21 (2004) 667
GEANT4
SOURCES
FLUKA
Fluka
Rock neutrons
Muon neutrons
GEANT4
see Kudryavtsev
SNOLAB meeting
Detector neutrons
YES
Higgs05
10-9/10 pb is possible with xenon with current technology
Path of no detection - 10-10-10-12pb
10 - 100
Tonnes
10-10pb
(1 unit)
1-5
ct/yr/ton
10-11pb
more neutron issues
Rock
Muon
Carson et al (submitted)
Detector (~1.5 tonnes inside
shielding - 1 tonne modules)
40 g/cm2
CH2
g/cm2
@ 3000 mwe - ok
~no veto (2x10-10 pb
at Boulby)
conclusion:
Needs <0.05 ppb U/Th (Cu,
and shielding, detector)
no internal neutron vetoing
no external neutron vetoing
@ 4500
mwekg)
- okprobably
Needs
< 5 ppt U/Th
multiple50small units
(100s
unsuited
CH
(10 units)
(e.g. Modane?) or
-9/10 ppt
for 2reaching
below around 10~10
pb with internal vetoing
0.1-0.5
(1) ct/yr/ton
must remove
(2) go for larger
10-12pb
(100 units)
0.01-0.005
ct/yr/ton
Higgs05
@ 3000 mwe with
~30 ppt with also external veto
walls
best vetoing gains
PMTs 90%
- goveto
for on
bulk
charge i.e.
readout
only about
single detectors with a fiducial
cut x 6 improvement
60 g/cm2
CH2
@ 6200 mwe - ok
[SNOLAB=7000] or
@ 3000 mwe with
99% muon veto
(probably ok due to
passive effect needs large
coverage)
Needs < 0.5 ppt U/Th
<3 ppt with vetoing
or some other ideas
Higher internal purity or fiducial cut
Note: (1) neutron absorption length in LXe (or Ge) ~10m
--> so passive LXe neutron shield no good
(2) but neutron MFP in LXe (or Ge) ~15cm
--> so can use detection to define fiducial volume
large single phase liquid Xe with fiducial cut
- NO  discrimination -
LSXe: option 1
volume for shielding
fiducial volume
n
PMTs
30cm outer volume should suppress
neutrons by ~x10 (60cm by x100...) but
needs position sensitivity to define two
regions (e.g. 1 cm)
i.e. like XMASS...
Higgs05
10 ton detector
Make single phase Xe big
- XMASS
100kg Prototype
800kg detector
～30cm
～80cm
R&D
～2.5m
Dark matter search
Now
Higgs05
Multipurpose detector
(solar neutrino,  …)
Option 2 - charge readout
see P.K. Lightfoot talk at Paris TPC meeting Dec 04
quite well understood now (Sheffield group):
conclusion with Micromegas
Xe gas + CH4
Lq Xe
Higgs05
25cm trials
(1) Micromegas
CH4 quench25
in xtwo-phase
ok
(2) CH4 % can be optimised
(3) micromegas gain at 1.8-2.0 bar ok
(4) hole size/pitch can be optimised
(5) drift field can be optimized
Dream 10-12pb LSXe Experiment
thanks to Hanguo Wang, Yannis Geomataris for discussions
plot stolen from NOSTOS
(Giomataris) [gas TPC]
Features
• CsI photocathode over entire sphere
inner surface makes use of known good
300 kV feedthrough!
CsI
electron
transport
~10m gas TPC
NOSTOS
spherical
4+mICARUS
(Wang etcoating
al)
5 ms lifetime measured at 2mm/mm = 10m Wang et al.
• 100 tonne mass (20-60 fiducial)
• 300-400 kV central feedthrough
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
• Charge readout in liquid by micromegas
(5kV/cm) or nano-tips
Giomataris
- Saclay
• Fiducial defined
by reconstruction
of
charge distribution
• High efficiency means no need to
extract recoil ionisation (better if can)
micromegas
or
HV feed with
nano-tip readout • Recoil discrimination (unlike XMASS)
shaping rings
Higgs05
A SIGNAL!
but can it be true?
but is it galactic?
Higgs05
Direction sensitive detectors
WIMP Wind
12:00h
42o
Galactic
WIMP
Halo
0:00h
WIMP
v0

MC ~30 WIMPs to
confirm galactic
isotropic
recoil
cos
Higgs05
Determine
galactic origin
WIMP
astrophysics?
Death of the Standard Model?
Models: many structures
• velocity space anisotropy
• bulk rotation
• substructure, clumps
• ultra-small scale clumps
• triaxality, logarithmic ellipsoidal
• oblate vs. prolate
• late accreted sub-halos
• sub-structure on sub-pc scales
• spikes and caustics
Clumps
Moore et al.....
Multicomponents
Tidal disruption
streams - Sagittarius
Evidence:
• rotation curves
• local kinematics, Oort constants,
• tracers: satellites
(PNs, globular clusters, halo stars)
• IR maps
Stiff , Widrow et al..
Helmi et al, Evans et al...
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
K. Johnston et al, Sackett &
Merrifield reviews
Freese, Gondolo et al.
New satellite missions
Sun’s influence
Higgs05
Fu-sin Ling et al.
Sikivie, Wick et al
Low pressure TPC
Scattered
WIMP
Simulated
events
SRIM 40 keV S recoils in 40Torr Cs2
the DRIFT Collaboration
(UKDM) Imperial College, RAL, Sheffield, Edinburgh,
Occidental College, Temple, Universityelectron
of New Mexico*,
CS
(+)
Recoil
Boston University*, Thessaloniki , Darmstadt(+)
Atom
*new, +new for KK axions
electron track
2
of similar
energy is off
scale (sketch)
Ionisation drift
Electric
Field
Readout
Plane
negative ion drift with CS2 idea by Jeff Martoff (Temple)
Higgs05
How many WIMPs to see the halo
AIM: how many WIMPs to see the halo?
[B. Morgan, A. Green, N. Spooner - Astro-ph/040804]
40 keV S recoil in 40 Torr CS2
(this is a simulation)
Model for realistic (advanced) detectors
• 40 Torr CS2
• 1 kVcm-1 drift field
• 200 mm resolution
• 10 cm drift
• SRIM2003 - recoil scattering and diffusion
Vectorial Statistics:
Axial Statistics:
Recoil directions estimated as principal axis ±r
of moment analysis of pixel signals.
predictions for TPC-type detector
Recoil sense known(unknown): 10-20(100-400)
events
needed
to reject
with
200 mm
resolution
isotropy at 95% confidence in 95% of experiments.
primary limitations: (1) recoil scattering and diffusion
(2) head-tail
Higgs05
B. Morgan
A. Green
Programme - DRIFT I,II...
[Alner et al. - NIM A 535/3 p644 ]
DRIFT-I @ Boulby
DRIFT I: - 2002/4 technology r&d
(UKDMC, Temple University, Occidental College)
• 1m3 Dual Negative Ion DRIFT TPC
• Back-to-back 0.5m3 DRIFT regions.
• 1.4m3 vac vessel - 40 Torr CS2
Technology achieves  rejection (<10-5/6)
No need for Pb shielding in DRIFT I
R2
Example 252Cf - uncut
data
2D sensitivity
gamma
region
neutrons
(simulated WIMPs)
Energy (NIPs)
Higgs05
DRIFT II (A,B,C....) - multi-module
•
first steps to cheap modules
x 20 improvement in sensitivity of D-I
Scaleable for D-III
•
E drift
0.135.m
0.5m
E drift
0.5m
Basic Design
Modular… n (3-4)  1m3 fiducial vol, NITPCs
• Back-to-back drift vols & dual MWPC readout
• Vertical planes, Warp adjust strongback MWPCs
• 3d track reconstruction (anode, grid and z-drift)
(Improved resolution: x = 2mm,  y = 0.1mm,
 z = 0.1mm)
• Lower noise DAQ (few keV S-recoil threshold)
• Improved vessel design (<10-5T.L.s-1) .
• Improved gas system (various pressure &
gas mixtures)
Higgs05
0.14m
Aim
Skate plate
0.09m
Sensitivity Note
This technology also good as a non-directional search experiment
• add 50% Xe
• increase pressure by x4
• throw away directionality but retain gamma discrimination
• RESULT: full DRIFT II @ 160 Torr, 50:50 CS2:Xe
could reach 10-9 pb
Higgs05
DRIFT II (A) - construction
MWPC, 1m2
assembly of field cage
vacuum vessel
DAQ
Higgs05
DRIFT II (A) installation
Low BG
Lab
Data acquisition
Exhaust CS2 sensor
system
Detectors / Vacuum
Chambers
3 2 1
ZEPLIN - II
DRIFT-I
Lab
Entrance
corridor
CS2
sensor
Higgs05
ZEPLIN - III
>2.0m
>2.0m
JIF CS2 sensor
Mess
Gas/fire sensor
control
gas systems, fume hood
& extraction hose
Boulby lab is now a clean room
Now a class <2500 clean room
Air shower
Stub B
Stub A
Low
Background
Lab
Air shower
DRIFT-I
Lab
Change area
Mess
Gas/fire sensor
control
Workshop
Store
Higgs05
ZEPLIN - II
DRIFT -II
Phase B
ZEPLIN - III
DRIFT -II
RED - clean
room
class 2500
or better
Materials clean-off
New low background test lab
5.6m
Installation of 2T anchored swing crane.
Installation of HEPA air filtration.
LB Lab plan
Bench
GE 1
AC unit
EU FP6
ILIAS
GE 1
GE 1
7.68m
Small Proj Bay
11.96m
0.8m
0.5T swing crane
(in place)
Project Assembly
Area
Desk 4.28m
LB lab - with HEPA
air filtration.
HEPA
6.0m
2T anchored swing crane
Higgs05
Entrance
Clean-Off
6.0m
DRIFT II(a) - First test data (surface)
Raw Data
Fe55 Calibration
1st DII-A MWPC
MWPC1
 particle
Higgs05
cosmic neutron
MWPC2
Also do KK axion search (preliminary)
BASIC LIMIT - Add Pb shielding until vessel background dominates (10 cm for 1 ppb)
B. Morgan, N. Spooner, D. Hoffmann, K. Zioutas (paper accepted in Astrop. Phys)
[1 m3yr, CS2, 160 Torr, amass 6-20 keV, 1 ppbU/Th in vessel]
ga GeV-1
-1
g
GeV
TPC
a

a


E
unshielded
15 cm Pb
R
T
n0 m-3
LSP, LKP, KK axion and directional
Higgs05
The Ultimate Dream Detector?
halo sensitivity at 10-12pb (2020+?..)
Basic numbers for worst case cross section
Exposure, Mass
Depth
1000 ton.yr (galactic
CS2
Fe55 5.9keV
confirmation), 10,000
spectrumton.yr
>4000 mwe (ignores statistical discrimination of neutrons via isotropy)
(if) Gas technology
go for 1 atm. (easier vessel?)
50 mm track mmgas readout (interpolation)
3 kg/m3 target
1cm readout plane spacing (2d/3d)
diffusion subtraction
Caverns
3 caverns of 2km x 10m x 5m
Low background components ok: Lucite, Cu, Kapton
Higgs05
(halo confirmation)
Messages to take home
• Recent rapid progress
•
General
MSSM
NOW: CDMS, Edelweiss, ZEPLIN…
sensitive to SUSY models - 10-6/7 pb
(detection could be very soon)
then
• ~2 YEARS: Several experiments expected
reach to 10 pb
no knownto unknowns
• ~5 YEARS: Technology for 10 pb (1 ton)
and
looks possible particularly with Xenon
no unknown
knowns
• ~10 YEARS: Technology for directional
-8
-10
detectors at 10-10pb (1 ton) also looks
possible now - it’s important to be ready
with directionality
100
Higgs05
mC(GeV)
1000