Transcript Searching For Dark Matter in the Universe:

Searching For Dark Matter in the Universe:
Direct (indirect) methods for the detection of Weakly
Interacting Massive Particles (WIMPs)
PIC -2004
Nader Mirabolfathi
University of California,
Berkeley
1
Evidence of Dark Matter: At Galactic scales…
• Rotation curve of spiral
galaxies imply the presence
of dark matter
m
 Expect v2  1/r
M
 Velocity is measured using atomic lines
from stars or the 21cm H line for the
hydrogen clouds around the galaxy
halo
sun
bulge
disk
 If WIMPs are the halo, detect them on earth
Bergstrom, Rept.Prog.Phys. 63 (2000) 793
E. Corbelli & P. Salucci astro-ph/9909252
via scattering on nuclei in targets
2
Evidence of Dark Matter: At Cosmological scales…
2003
Many different approaches:
• Cosmic Microwave Background
• Clusters of Galaxies
• Supernovae SN1a
ΩL
• Large-Scale structure formation
 All agree that matter makes up
approx. 27 % of the Universe
and…
... Big Bang Nucleosynthesis, CMB,
and Structure Formation require that
approx. 85% of the matter is Non
Baryonic Cold Dark Matter
Ωmatter
3
Standard Model of Cosmology
Many CDM candidates:
• SUSY neutralinos
• Axions
• Gravitinos
• Kaluza-Klein states
• ...
4
Candidate: Weakly Interacting Massive Particles
• WIMP c : produced when T >> mc via
annihilation through Z (+other channels).
Production = Annihilation (T≥mc)
Production suppressed (T<mc)
• If interaction rates high enough,
comoving density drops as exp(- mc/T) as T
drops below mc :
Freeze out
• Annihilation continues
• Production suppressed.
~exp(-m/T)
 Freeze out when annihilation too slow
to keep up with Hubble expansion
 Leaves a relic abundance:
c h2 10-27 cm3 s-1 ann vfr
For c~0.3:
• M ~ 10-1000 GeV
• A ~ electroweak
1
100
10
mc / T (time )
1000
5
Direct Detection of WIMPs
If WIMPs are the halo, detect them via elastic scattering on nuclei
in targets (nuclear recoils)
WIMP
detector
Energy spectrum & rate depend on target
nucleus masses and WIMP distribution in
Dark Matter Halo:
Standard assumptions:
Measure recoil energy
 Isothermal and spherical
 Maxwell- Boltzmann velocity distribution
V0=230 km/s <V>= 270 km/s,  = 0.3 GeV / cm3
Log(rate)
Energy spectrum of recoils ~ falling
exponential with <E> ~ 15 keV
Rate (based on nc and  ) is of the order of a
fraction of 1 event /kg/day
Erecoil
6
Experimental Challenges
WIMPs: Extremely small scattering rate, small energy of the recoiling
nucleus, and subtle signatures…
Requirements:
 Low (keV) energy threshold
 Large target mass
 Suppression of backgrounds from radioactivity and cosmic
rays (,,, neutrons)
• Deep sites
• Passive/active shielding
 Discrimination of residual background
• Use WIMPS signatures
WIMPs Signatures:
• Nuclear recoils, not electron recoils
• Absence of multiple scattering
• Annual modulation
• Directionality
7
WIMPS Detection Methods (strategies)
1)
i.
ii.
Increase the mass of the absorber and keep
the background as low as possible.
,,
 Electron
recoil
But how to distinguish WIMPs?
Cosmological signature for the WIMPs assuming
standard halo model.
Statistically remove the background.
Sensitivity improves by 1/(MT)1/2
2) Discriminate WIMPs against dominant back
ground (, , ). EVENT BY EVENT
i.
ii.
How?
WIMPs are interacting with nucleons whereas , , 
interact with electrons.
Increase the mass.
Sensitivity improves by 1/(MT)
c0, neutrons
 Nuclear recoil
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Current Direct Detection Experiments









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DAMA-NaI Experiment
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DAMA - 100 kg NaI Experimental Apparatus
• Very elegant experimental setup - in
place >1996
– Annual modulation: ~2%
modulation amplitude
POSITIVE SIGNAL
NaI
NaI
PMT
NaI
PMT
• Low Activity NaI scintillator
9  9.7 kg NaI crystals,
each viewed by 2 PMTs
• Located at Gran Sasso
Underground Lab (3.8 kmwe)
+ Photon and Neutron shielding
• Two modes of Background
discrimination
– Pulse shape
NaI
Copper
Lead
Polyethelene
11
Annual Modulation of Rate & Spectrum
WIMP Isothermal Halo (assume no co-rotation) v0~ 230 km/s
galactic center
Sun 230 km/s
Dec.
v0
Combining earth and solar system motion around galaxy
v  v 
v  v 
 v0 
min
e
min
e 
erf 

TQ 
 erf 




4ve 
 v0 
  v0 


2  t  t 
p 

where ve  v0 1.05  0.07cos
 1 yr 



:
log dN/dErecoil
June
Earth 30 km/s (15 km/s in galactic plane)
Dec
~5% effect
June
t p  June 2  1.3 days
Erecoil
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Annual Modulation
• Not distinguish between WIMP signal and Background directly
• From the amplitude of the modulation, we can calculate the
underlying WIMP interaction rate
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105
100
103
WIMP Signal
75
101
±2%
99
50
Background
25
97
95
0
-0.5
Dec
-0.1
0.3
June
0.7
Dec
1.1
1.5
June
-0.5
Dec
-0.1
0.3
June
0.7
Dec
1.1
1.5
June
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Modulation Amplitude
Best fit to
Ann Mod
data alone
Minimum
DAMA NaI/1-4 (3)
• There is clearly a modulation
(4 - compared to null hypothesis)
Best Fit
DAMA NaI/1-4
• Best-fit WIMP model’s expected annual
modulation does not appear to fit data;
lowest point of 3 contour is much worse.
• Why? Additional constraint applied during
max likelihood analysis: DC WIMP signal
implied by AC signal must not exceed
observed DC count rate
 best-fit cross-section is decreased
mean over 2-6 keVee
(22 – 66 keV recoil)
DAMA 2000 paper Figure 2
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DAMA 1
5,000 kg-day
DAMA 2
15,000 kg-day
DAMA 3 + 4
38,000 kg-day
DAMA → LIBRA
•
3 more annual cycles acquired
– 58,000 + 49,800 = 107,800 kg-d
– 7 cycles total
•
Improved DAQ
– Multiple scatters?
•
LIBRA
–
Large sodium Iodide Bulk for
RAre processes
– 250 kg with improved radiopurity
– Taking data. Results have not
been announced.
•
Further R&D toward 1-ton
– NaI(Tl) radiopurification started
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ZEPLIN
ZonEd Proportional scintillation in LIquid Noble gasses
Or
Zoned Electroluminescence and Primary Light In Noble gasses
Location: Boulby Mine UK: UKDMC
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Why Xe?
• Available in large quantities.
• High atomic number (A=131) gives a
high rate due to WIMP-NucleonA2 (if E is
low).
• High density (~ 3g/cm3 liquid).
• High light (175 nm) and ionization
yield.
• Can be highly purified.
long light attenuation (m).
long free electron life time (~5ms).
• Easy to scale up to large volume.
• No long lived radioisotopes.
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Principle Of Detection
Excitation
• Production and Decay of excited Xe2* states:
1)Through singlet (3ns)
2)Through triplets (27 nS)
• dE/dx determines the proportion of different
channels=>
Nuclear more dense give more singlets or faster
Ionization
•Ionized state Xe2+, recombine with e- =>
Xe2* =>Above relaxation
dE/dx determines the recombination time
channels=>
Nuclear recoils (ps scale) electrons (40 nS)
Nuclear recoils are faster
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ZEPLIN I
• Recombination allowed.
• Only scintillation signal measured.
• Discrimination is based on the pulse shape.
• Discrimination is statistical.
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ZEPLIN I Results
Linear response 1.5 p.e/keV
(E)=1.24E1/2
30 keV
90 keV
122 keV&136 keV
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ZEPLINI Results (continued)
•Fiducial mass =3.2 Kg
Mean event rate 2Hz.
•Trigger three fold
coincidences at 1pe.
•2keV threshold.
•Light yield 1.5-2.5pe/keV.
•Statistics 293 kg.day in Three
runs.
2003
2004
2002
2003 (SUF)
2002
No in situ neutron
calibration
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
21
LTDs, phonon sensors and beyond!
Who?
• CDMS (Cyogenic Dark Matter Search)
• EDELWEISS (Expérience pour DEtecter Les WIMPS En Sites Sousterrain)
• CRESST (Cryogenic Rare Event Search with Superconducting Thermometers)
Low Temperature Detectors
LTD-1 2001
LTD-9
1987
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LTDs, phonon sensors and beyond!
Why? Advantages?
• After an interaction (event), all the excitations transform to heat.
 Good resolution
• Phonon excitation~10-6eV compare to ~1or few eV for conventional
semiconductor detectors.
 Low threshold
How to measure: Two methodes
Temperature: Equilibrium
Advantages:
•T=E/C
Detecting theC(T/
overall T
3  No position
D)
dependence.
 T could be big even with keV
• Best resolution obtained with this kind of
interaction.
detectors:~100 eV at 5 MeV ?
Using thermometers
(Mott-Anderson
Weak points:
Superconducting
thermometers)
to
•orCMass
 Hard to increase
the detector
measure T.
mass.
• Unable to reconstruct the history of evts.
Lattice excitations (phonons)
Advantages:
•Low
Could
of anexcited
event.
T reconstruct
 Densitytheofhistory
thermally
•phonons
Thermometer
collects
constant
(noise)
is very
low. fraction of
phonons  independent of the absorber Mass.
But we need to collect phonons before
they reach the Equilibrium
Weak points: in the
•absorber.
Dispersion or position dependence of E.
low T Electron-phonon
interaction is
•At
Homogeneity
of thermometers.
more effective than ph-ph interaction
23 
evaporated thermometers (electron bath).
d4> d3> d2>d1
d4
d1
d2
d3
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Comparison between the two types of signals
B) Phonon measurement
A) Temperature measurement
Thermometer
Thermometer
To cold bath
Absorber
To cold bath
Absorber
T=E/Ctotal80
300
60
200
T=E/Cfilm
T=E/Ctotal
40
100
20
0
0
0.0
0.0
0.2
0.4
0.4
0.6
0.8
0.8
1.0
1.0
0.0 0
0.0 5
0.1 0
0.1 5
0.2 0
0.2 5
0.3 0
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Heat is not enough!
Need another measurement to achieve event by event discrimination.
Charge?
• The amount of charge created in a Semiconductor after an event depends on the type of
interaction: Quenching factor (Q).
• Quenching factor for an electron recoil event (Most of the radioactive background) is
bigger than for nuclear recoil events (WIMPs).
• By simultaneously measuring the charge and heat, one can discriminate - event by event
WIMPs from the background.
This defines the principle of detectors for CDMS and EDELWEISS
experiments.
Scintillation?
CRESST: The same principle but scintillation instead of charge.
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What is different between CDMS and EDELWEISS
• Collection E field needs to be very low
~3Volts/cm.
Dead layer (~50 m) > than traditional SM
detectors (~1 m). limits discrimination!
• Most of the  bkgnd falls into DL region.
very important to deal with.
Solutions
Identify
surface
events:
Avoidnear
surface
event
by:
1) Using phonon signal. Only possible if
1) Carefully dealing with surface contamination.
athermal phonons measured.
2) Introducing a blocking layer against the charge
(CDMS current, EDELWEISS R&D)
back diffusion  Introducing an
2) Using charge signal rise time. Needs a
amorphous Si layer below charge
large bandwidth electronics.
electrodes. Decrease DL to < 10 m
(EDELWEISS R&D )
Electron recoil
Nuclear recoil
Dead layer
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•Use of Ge NTD thermistors : FET readout
•The guard electrode ~50% volume
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• CDMS Soudan first result with towerI
• Tower I: 4 Ge (250 g) and 2 Si (100 g)
• CDMS now running two towers 6 Ge and 6 Si
• Si and Ge combination helps to better
understand the neutron bkgnd.
• Edelweiss 2002 1 Ge (320g) detectors No Si
• Edelweiss 2003 3 Ge (320g)
FET cards
SQUID cards
4K
0.6 K
0.06 K
0.02 K
ZIP 1 (Si)
ZIP 2 (Si)
ZIP 3 (Ge)
ZIP 4 (Si)
ZIP 5 (Ge)
ZIP 6 (Si)
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Shielding
Active Veto (reject events associated with
cosmics)
Hermetic, 2” thick plastic scintillator veto
Layeredaround
shielding
wrapped
shield(reduce , , neutrons)
~1 cm Cu
wallscosmic-ray
of cold volume
(cleanest
Reject
residual
induced
eventsmaterial)
Thin “mu-metal”
shield (for
SQUIDs)
Information
storedmagnetic
as time history
before
detector
10 cm polyethylene (further neutron moderation)
triggers
22.5 cm>Pb,
inner efficiency
5 cm is “ancient”
in 210for
Pb)
Expect
99.99%
for all ,(low
> 99%
40 cm polyethylene
(main neutron moderator)
interacting

MC indicates > 40% efficiency for -induced
showers from rock
30 cm parafin, 20cm Pb ,1 cm Cu
No active veto
Dilution fridge : 17mK base.
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CDMS 2004 Results (Calibration  cuts)
Charge spectrum
Electron recoil
4 Ge (850g) 2 Si (170 g) * 52 live days during 92 calendar days
• Neutron calibration after the run and Systematically check for
gamma (e-recoil) calibration. 
• Phonon position dependence removed. 
• Nuclear and electron recoil bands defined (+/- 2) 
• Phonon timing cuts defined with calibration data. 
• Guard charge electrode defined. 
• Veto coincident events defined (window 50 s). 
Nuclear recoil
• Selection criteria and nuclear recoil efficiency
• Veto coincidence (50 us window) - 97%
• Baseline stable (pileup, noise,…) - 95%
• Nuclear Recoil band (2 sigma)
- 95%
• Phonon Timing cuts
- 80%
• Charge outer electrode cut
- 75%
• TOTAL
- 53%
Phonon Spectrum
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WIMP search data with Ge detectors
– 92 days (October 11,
2003 to January 11,
2004)
– 52.6 live days
– 20 kg-d net (after cuts)
Charge yield
• Exposure
• Data: Yield vs Energy
– Timing cut off
– Timing cut on
– Yellow points from
neutron calibration
Recoil energy (keV)
32
WIMP search data with Ge detectors
– 92 days (October 11,
2003 to January 11,
2004)
– 52.6 live days
– 20 kg-d net (after cuts)
Charge yield
• Exposure
• Data: Yield vs Energy
– Timing cut off
– Timing cut on
– Yellow points from
neutron calibration
Recoil energy (keV)
33
WIMP search data with Ge detectors
– 92 days (October 11,
2003 to January 11,
2004)
– 52.6 live days
– 20 kg-d net (after cuts)
Charge yield
• Exposure
No nuclear-recoil
candidates
• Data: Yield vs Energy
– Timing cut off
– Timing cut on
– Yellow points from
neutron calibration
Recoil energy (keV)
34
Comparing Cross section-WIMP Mass plots
35
Future
• The presented results are from one tower
• CDMS II is now running two towers (6 *Ge
(250 g) 6 *Si (100 g)
• Background of the second tower is very
similar to tower I.
• Run stops mid July of this year
• New three towers of detectors will be installed
October this year
• CDMS II ends by the end of 2005.
• March 2004 end EDELWEISS I
• Install EDEWEISS II with 21*320 g Ge NTD+
Install 7*400 g NbxSi1-x athermal phonon detectors
(Dead layer rejection)
• The 100 liter dilution fridge has been successfully
tested. Capacity for 120 detectors or 35 Kg Ge
36
CRESST : Scintillation/Heat instead of Charge/Heat
Gran Sasso
• Background discrimination by simultaneously measuring light/heat.
• Uses a cryogenic detector (the same as phonon detector) for light
measurement.
• Works with different absorber materials: CaWO4 (mainly), PbWO4,
BaF,..Advantage to change the absorber
• Phonon channel:320 g CaWO4 (=40mm,h=40mm) , W-SPT (4*6 mm2).
• Light channel:30*30*.4 mm3 W-SPT. Need 33 Modules to complete
• Reflector: Polymer foil, Teflon.
CRESST II goal
37
CRESST Sensitivity and rejection
• High rejection:
99.7% E > 15 keV
99.9% E>20 keV
• 9.7 kg.day data
•Only half of the data analyzed.
• Data without neutron shield.
•Sensitivity limited by n.
38
Future direct detection experiments
39
DRIFT experiment
Directional Recoil Identification From Tracks
• Standard halo model for WIMPs in our galaxy suggests that
the axis of recoils changes in the 24 hours (earth).
• Axis of recoil is a cosmological signature for WIMPs.
• Ionization track in a low pressure gas (CS2) depends on the
type of interaction (Discrimination).
• Multi wire proportional chamber ?
40
Principle of DRIFT
E
eC+,S+
WIMPS

Si
Time of flight
z
41
DRIFT setup
• Low Prsure CS2 (40 Torr) 1 m3, 0.167 kg, 20 micron
diameter wires 2 mm pitch.
• 1 mm track for nuclear recoils
• Many calibration runs with 55Fe (5.9 keV X-rays)
• Neutron Calibration with 252Cf.
• Polypropylene shielding (~ 50 cm).
• Dark matter run started.
• Energy threshold 15 keV.
gammas
C recoils
S recoils
42
Discrimination in ZeplinII and III,IV,…
Double phase Xe : Ionization
Calibration of the prototype with
gamma and neutron sources
showed very good gamma/neutron
discrimination
(Cline et al. Astroparticle Phys. 12(2000)
373)
43
~3Kg
~30kg
~1000 kg
ZEPLIN I
ZEPLIN projected
ZEPLIN II
ZEPLIN IV
44
Xenon: Perspective
•
•
•
•
•
•
•
•
Dual phase Xe experimnent
Light/Ionization
Very-low BG PMT
Prototype 1 cm drift
10 kg prototype underway
100 kg phase : 1 TPC
Modular: each module 100 kg
Self protected by outer Xe
•
•
•
1 Ton scale
99.5 % discrimination eff
16 keV threshold
45
WIMPS indirect detection experiments
• AMANDA , ICECUBE (Southe po;e)
• ANTARES
• NESTOR
• Superkamiokande, Hyperkamiokande
•  -ray telescopes: CANGAROO, MAGIC, HESS
• Satellite experiments: AMS-02, GLAST
46
WIMP indirect detection
•WIMP elastic scattering. But in average it will lose energy:
•V<Vescape accumulates in the center of large massive
objects like the sun earth or galaxy.
•Neutralino : Majorana particle  its own anti particle.
•If massive annihilates.
•Annihilation ;b,c,t quarks;gauge and Higgs Bosons
,,,e+, p-.
•Signature:
search for excess of up-going muons
•Form direction from center of sun galaxy or Earth.
•Search for annihilation lines (galactic center, cosmological…)47
Neutrinos from the center of the earth, sun, galaxy.
Assumptions:
•Dark matter in the galaxy due to c
• Density~ 0.3 GeV/cm3
AMANDA, Super K…
48
AMANDA
South Pole
Dome
AMANDA
1500 m
Summer camp
49
Amundsen-Scott South Pole station
2000 m
[not to scale]
AMANDA
AMANDA-II
19 strings
677 OMs
Trigger rate: 80 Hz
Data years: 2000-
Optical Module
PMT noise: ~1 kHz
50
WIMP annihilations in the center of Earth
Sensitivity to muon flux from neutralino
annihilations in the center of the Earth:
xx  qq, l  l - , W, Z, H   
Muon flux limits
Look for vertically upgoing tracks
NN optimized (on 20% data) to
- remove misreconstructed atm. μ
- suppress atmospheric ν
- maximize sensitivity to WIMP signal
Eμ > 1 GeV
Combine 3 years: 1997-99
Total livetime (80%): 422 days
Disfavored by
direct search
(CDMS II)
No WIMP signal found
Limit for “hardest” channel:
xx  τ  τ -   
xx  W  W -   
M x  50 GeV
M x  100 - 5000 GeV
51
CDMS 2004
52
Summary
• Direct detection Experiments (CDMS,EDELWEISS, CRESST..) have already
explored the regions of the most optimistic SUSY models.
• Despite the lower amount of exposure (~20 kg.day compare to 110,000 kg.day),
the event-by-event discrimination methods are giving the best sensitivities.
• Extremely high discrimination + large mass seems to be the only solution for the
next generation of direct detection experiments.
• The current and next experiments (CDMSII, EDELWEISSII, ZEPLIN IV, XENON
…) will explore the core of many SUSY models in few years.
• Indirect detection will be complementary but hardly competitive to low  scalar
WIMPs detection.
• The accelerator (LHC) results + the direct detection experiments will soon (not in
the cosmological sense!) let to discover the nature of the dark matter.
53
54
Modulation Animation in NaI
50 GeV WIMP
Sun
moving
through
WIMP
Halo
Threshold
Background
56
000904.4 rjg
Muon flux: 4/m2/day
Neutron flux:1.5e-6/cm2/s
Log10(Muon Flux) (m-2s-1)
Log10(Muon Flux) (m-2s-1)
Muon flux: 70/m2/day
Neutron:
Depth (mwe)
Depth (mwe)
57
WIMP search data with Ge detectors
– 92 days (October 11,
2003 to January 11,
2004)
– 52.6 live days
– 20 kg-d net (after cuts)
Charge yield
• Exposure
Well, maybe 1….
• Data: Yield vs Energy
– Timing cut off
– Timing cut on
– Yellow points from
neutron calibration
Recoil energy (keV)
58