Indirect detection of Dark
Matter
…. from an experimental point of view ….
Jan Conrad
conrad.at.fysik.su.se
A Decade of New Experiments
XXXVII SLAC Summer Institute,
August 3-14, 2009.
The reason why I am not at SLAC
Ellen, 14 month
09-02-02
/
Me
Thanks for suggesting this solution to
Greg Madejski and JoAnne Hewett
(we’ll see if it works).
• Questions can be adressed to me by mail:
conrad@physto.se (there are no stupid
questions!)
• During lectures I usually try to read the
audience, which will not be possible  positive
and negative feedback would be very useful (via
mail).
09-08-07
Jan Conrad, Stockholm Universitet
3
Goal for the lectures.
• You should understand the experimental
approaches to indirect detection of dark matter
and what we can expect in the next decade.
• You should understand that DM indirect detection
is challenging and what the challenges are
• I hope I can give you some additional insight in
what to make of the presented results.
• I hope I will be able to convey the message that
revolutions are on the horizon.
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Jan Conrad, Stockholm Universitet
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Contents and non-contents
• Not in this lecture(s):
– Why DM ?  Tegmark,Weiner
– DM candidates  Weiner
– Results will be presented mainly if they illustrate a special point
 for newest results: see talks by Moskalenko, Pearce, Burnett, Egberts
• Lecture I
– Preliminaries (minimal theoretical background)
– The set up
– Charged cosmic rays,
• Signatures
• Astrophysics and backgrounds
Also important for
– A detour cosmic ray diffusion in the Galaxy
gamma-rays --– Instrumental background
lecture II
• Experimental approaches
• PAMELA, ATIC, FERMI results on charged cosmic rays.
• GAPS
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Jan Conrad, Stockholm Universitet
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• Lecture II
– Gamma-rays
• Signatures
• Astrophysics and backgrounds
• Experimental approach and experiments
• Source confusion
• Selected Results
– Neutrinos
• Signature
• backgrounds
• Experimental approach and experiments
• Selected results
• Impact of Astrophysics
– Interplay between different indirect experiments
– Indirect indirect detection (multi-wavelength)
Some additional slides contain more detailed information …
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Jan Conrad, Stockholm Universitet
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The set-up
• Prime DM candidate: Weakly Interacting Massive
Particle (WIMP), denoted by c
• Mass: ~ 10 GeV - ~ 10 TeV
• ”Weakly” interacting
• Experimental signatures (roughly) applicable to a
variety of candidates:
–
–
–
–
Supersymmetric neutralino
Kaluza Klein
Axino, Gravitino, SuperWIMPs
….etc. etc.
• Other CDM candidates:
– axions ( discussed if time)
For motivation and theory: see Neil Weiners talk
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Jan Conrad, Stockholm Universitet
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The set-up: WIMP annihilation or decay
c
c
W-/Z/q
p0
W+/Z
p
/q
g
g
nm
m
nmne
e±
Anti-p, anti-d
Indirect detection rate = (particle physics part) × (astrophysical part)
PPP
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Jan Conrad, Stockholm Universitet
APP
8
Signal: general considerations
• Particle physics part orders of magnitude parameter space (x-sections)
– DM particle’s spin mass, annihilation cross section, branching fraction
into final states and yield for a given final state (given by underlying
theory (KK,MSSM, IDM etc).
 For experimentalist: Analysis optimized for given signature
PPP  v  Y (E )
• Astrophysical part
benchmark : v  3 1026 cm3 s 1
> Order of magnitude uncertainties
– (Density of DM particles)2, diffusion, absorption (where applicable)
 For experimentalists: Where to look for the signal?
More details in respective section. Note there is virtually no
experiment
dedicated
solely (or even mainly) to IDMD !!! (one
Jan Conrad, Stockholm Universitet
09-08-07
exception: GAPS …. will be discussed.)
9
Dark Matter on Galactic scales
Dark Matter on Galactic scales
Cosmic rays
c
e-+
W /Z/q
_
W+/Z /q
e-
c
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p
m
e±
Anti-p, anti- d
Jan Conrad, Stockholm Universitet
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Cosmic rays: signatures
Positron fraction
and spectrum
Antiproton fraction
and09-08-07
spectrum Jan Conrad, Stockholm Universitet
Anti-deuteron
spectrum
11
APP: cosmic ray propagation in the Galaxy:
why we need to talk about it:
• Cosmic rays produced in secondary processes provide a formidable
background to DM searches with anti-particles.
• Photon-production by Galactic cosmic rays provide a formidable
background to DM searches with gamma-rays
• Any potential signal in CR will need to be interpreted with effects of
the propagation in mind
Strong et al, ApJ 537, 736, 2000
Diffuse gamma-ray
Jan Conrad, Stockholm Universitet
09-08-07
prediction
1
Strong et al, ApJ 613, 962, 2004
Diffuse gamma-ray
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prediction 2
APP: cosmic ray propagatioin in the galaxy
To some:
To us:
Diffusion
reacceleration
convection
energy loss
Radiation field
spallation
decay
B-field
B-field
CNO
Gas
e
p
DM
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 π0  γγ
 π±  e±
Gas
p-bar,
Jan Conrad, Stockholm Universitet
 π±  e±
 π0  γγ
 Li, B 
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Many other experiments will be important
for indirect detection:
• By standard, quantitatively described by diffusion equation
(see additional slides) with a number of assumptions (e.g.
GALPROP code)
• Constrained through CR and gamma-ray observations
• Diffusion coefficient  Primary/secondary nuclei ratio (HEAO3, ACE,PAMELA,CREAM,TRACER)
• Interstellar radiation field:  optical,FIR,CMB (DIRBE, FIRAS)
• Interstellar gas (H1,HII) 21cm, CO surveys (Bonn,Parkes)
• B-field  radio surveys (Jodrell Bank, Parkes ,WMAP, Planck)
• Spallation, pion production cross-sections accelerators
09-08-07
Jan Conrad, Stockholm Universitet
For a more detailed
account: Moskalenko,
SSI 2008
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Cosmic ray anti-matter: detection
principle
Scintillator (TOF)
PID (TRD,Cherenkov)
magnet
Anticoincidence
(scintillator)
Scintillator (TOF)
PID (TRD,Cherenkov)
Calorimeter
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Jan Conrad, Stockholm Universitet
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1.2 m, 450 kg
1.5 m, ~6000 kg
Examples: PAMELA and AMS-02,
spectrometer
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Jan Conrad, Stockholm Universitet
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Examples for ”calorimeters”:
ATIC/FERMI/HESS
g
e e–
+
1500 kg,
h=1.2m
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Jan Conrad, Stockholm Universitet
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Example: PAMELA and ATIC
• Launched: June 15, 2006
from Baikonur,
• Three flights (2001,2003 and 2008)
• Quasi-polar orbit
• Total livetime: 50 days
• Expected livetime: > 3 years
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Jan Conrad, Stockholm Universitet
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Instrumental backgrounds for e+,e-,γ
Hadronic background is
dominant.
Necessary rejection
factors:
ATIC, Fermi electrons ~ 103-4
PAMELA, AMS ~ 104-5
Fermi γ ~ 105-6
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Jan Conrad, Stockholm Universitet
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Hadron/electron discrimination
• Main idea:
– Veto detectors (Anticoincidence)
– difference in shower
shape for em/hadronic
showers in calorimeter
– Background rejection
gets harder with rising
energy
– Full analyses apply
combined information
of several detectors in
multivariate
classification (Neural
networks …)
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Jan Conrad, Stockholm Universitet
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Example: Fermi electron analysis.
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Jan Conrad, Stockholm Universitet
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Anti-proton/proton ratio
500 days of data, 109 triggers, ca. 1000 anti-protons, ca. 107 protons,
background < 3 %
6 anti-protons
ca 600 > 5 GeV
O. Adriani et al. Phys.Rev. Lett.
102:051101,2009
09-08-07
Jan Conrad, Stockholm Universitet
Compatible with secondary
production
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Positron fraction: the PAMELA anomaly
500 days of data, 150 k electrons, 10k positrons
Errors include
background removal
uncertainty
Very soft electron
spectrum (index: 3.54) at odds with
Fermi (see later)
Conventional
production:
Delahaye et. al
arXiv:0809.5268
Conventional
production:
GALPROP
O. Adriani et al. Nature 458:607-609,2009
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Jan Conrad, Stockholm Universitet
Strong & Moskalenko
Astrophys.J.509:212228,1998
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Possible sources
• No extra source:
– Experimental M. Schubnell, arXiv:0905.044
– Non standard diffusion
• Extra source
B. Katz et al., arXiv:0907.1686
– Dark matter
– Conventional sources
• Pulsars
• Supernovae
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Jan Conrad, Stockholm Universitet
P. Biermann et al., arXiv:0903.4048
L. Bergström et al.,
Phys.Rev.D78:103520,2008
D. Malyshev et al. 0903.1310
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Pulsars invoked already 20 years
ago ….
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Jan Conrad, Stockholm Universitet
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e++e- spectrum: the ATIC anomaly
Based on ATIC 1 + ATIC2
ATIC collab. Nature 456, 362-365(2008)
Statistical errors
only,
background
subtracted
HEAT
BETS
PPBBETS
x
Emulsion
chambers
GALPROP
Sol. Mod.
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Jan Conrad, Stockholm Universitet
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Fermi-LAT as an electron detector
Fermi-LAT
effective
geometric
Factor
Energy resolution: ~ 20 %@ 1 TeV
(cf. ATIC ~ 2 % @ 150 GeV
cf. PAMELA ~ 6 % @ 200 GeV )
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Residual hadron
Cf: ATIC effective geometric factor contamination
Jan Conrad, Stockholm Universitet
(less for PAMELA)
< 20 %
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e++e- spectrum
A. Abdo (Fermi-LAT)
Phys.Rev.Lett.102:181101,2009
6 month of data
• ATIC is gone??
• Data is compatible
with power-law (3.04).
• Is there a
deviation from
power-law?
3.8 σ  5.1 σ , Isbert (ATIC, TANGO in Paris 2009)
One slide on possible explanations in appendix
Also see Eun-Suk Seo’s topical talk
ATIC:
F. Aharonian (HESS),
arXiv:0905.0105
±09-08-07
15 %
Jan Conrad, Stockholm Universitet
reject
KK model that fits ATIC at 99%
(including E resolution).
1724 events > 100 GeV
Fermi:
171431 events> 100 GeV
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…and explanations ….
• No extra source:
– Experimental (for ATIC)
– Non standard diffusion
D. Grasso et al., arXiv:0907.0373
• Extra source
– Dark matter
– Conventional sources
• Pulsars
• Supernovae
P. Biermann et al., arXiv:0903.4048
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Jan Conrad, Stockholm Universitet
Bergström et al. 0905.0333
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A remark on boost-factors
• The annihilation cross-section is set by DM
abundance in Big bang freeze out  not
sufficient to explain observed alleged signal.
• ”Boost” of rate has been invoked:
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DM substructure
e.g. Sommerfeld factor
~ 10??
~ 0-1000? (requires
modifications to model)
Jan Conrad, Stockholm Universitet
L. Bergström, arXiv 0903.4849
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If it is DM, what would it mean?
• Data prefers models with mostly leptonic annihilation
channels (in fact, muons)
• Most models predict rather large masses (> 1 TeV).
• This is hard to accomodate within MSSM considering
the anti-proton (gamma) constraint.
• Most models need an additional enhancement of
annihilation cross-section (”boost”).
• Most models make predictions which are testable
with soon existing data (gamma-rays).
One can ask how much sense it makes to do this considerations at this point
of time ….. some groups even publish theoretical analysis on preliminary
data …. which I think is not very useful (unless you go with
Carlo Rubbia (alleged): ”Better wrong than late” )
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Jan Conrad, Stockholm Universitet
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Cosmic ray detectors of relevance to DM
TRACER
PEBS
VERITAS
AMS
Fermi
PAMELA
HESS
future exp.
spectrometers
”calorimeters”
auxiliary
BESS-polar
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Jan Conrad,
Stockholm Universitet
PPB-Bets
ATIC
CREAM
GAPS
CALET
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Cosmic ray experiments: comparison
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Jan Conrad, Stockholm Universitet
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GAPS detection
principle
_
p*
D
Slide stolen from Jason Koglin,
Columbia U.
Atomic Transitions
Plastic Scintillator TOF
Si(Li) Target/Detector
Auger e-
no,lo
Refilling e-
p*
n=nK~15
44 keV
n=6
g
n=5
g
n=4
g
n=3
Ladder
Deexcitations
Dn=1, Dl=1
n=2
30 keV
p*
p*
A time of flight (TOF) system tags
candidate events and records velocity
The antiparticle slows down & stops in
a target material, forming an excited
exotic atom with near unity probability
Deexcitation X-rays provide signature
09-08-07
Jan Conrad, Stockholm Universitet
p+
n=1
p+
p
po
p
Nuclear
Annihilation
Pions from annihilation provide added
background suppression
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GAPS sensitivity
2011 prototype
2014 flight
GAPS white paper
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Jan Conrad, Stockholm Universitet
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Summary (cosmic rays):
• General:
– CR probe DM on Galactic scales
– Cosmic ray propagation in the Galaxy is important for gamma-rays
and cosmic rays  needs imput from a variety of experiments.
– Instrumental and astrophysical backgrounds are challenging.
– Anti-deuterons provide a potential smoking gun signal
• Status:
– PAMELA let the genie out of the bottle
– Signatures detected which could be the first sign of DM.
– The experimental situation is confusing with different (apparently) not
consistent results (ATIC vs. Fermi !, PAMELA vs. Fermi ?).
• Outlook:
– Future experiments (AMS-02,PEBS) and additional data will be
crucial:
• For constraining backgrounds for e.g. gamma-rays and cosmic
rays.
• For distinguishing signal hypothesis.
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Jan Conrad, Stockholm Universitet
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