Transcript Searches for Particle Dark Matter with gamma rays Jan Conrad CERN-PH Oskar Klein Centre Seminar Physics Department Stockholm University [email protected].

Searches for Particle Dark
Matter with gamma rays
Jan Conrad
CERN-PH
Oskar Klein Centre
Seminar
Physics Department
Stockholm University
[email protected]
1
Table of contents
•
•
•
•
•
Short Intro
A few results and predictions
The tentative Fermi-LAT spectral line
Conclusions
If time: three slides on complementarity
2
Who has never heard of this?
70%
25 %
3
Weakly Interacting Massive Particles (WIMPs)
The weak interaction mass scale and ordinary gauge
couplings give right relic DM density without fine-tuning.
Mass scale O(GeV)-O(TeV), makes them Cold Dark Matter
Wimp
1026 cm3 s 1

v
v ~ weak ~
2
2
WIMP
m
 25
3 1
~ 10 cm s
Jungman+, Phys. Rept. (1996)
Will not talk about axions1, WISPs (sub-eV), sterile neutrinos (keV) …
4
Detection of Dark Matter
Indirect detection rate = (particle physics part) ×
(astrophysical part)
X-section
Yield
v  Y ( E )
PPP 
m2
APP   ddl  2 (l )
DM density,
”J –factor”
WIMP mass
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Universal spectral signatures Y(E)
Ullio et al. Phys.Rev.D66:123502,2002
  ...  p 0  gg
Birkedal et al.,
  (Z,g)g
Bringmann et al. JHEP 0801:049,2008.
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APP- smooth Dark matter halo density profile
Cosmological
N-body
simulations:
 NFW (r ) 
c
r (a  r ) 2
Einasto (r )  exp( Ar )
NavarroFrenk-White
Einasto
 ”Cuspy”
Stellar
dynamics:
 Bur ker t (r ) 
c
(r  a)(a 2  r 2 )
We are
here
e.g. Burkert.
 ”Cored”
R. Catena
Strongest signal from the Galactic Center !
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APP- ´substructure
We are here
No Baryons, including them is work in progress –
potentially interesting effects
8
Experimental implications
• Particle physics part
– DM particle’s spin, mass, annihilation cross section, branching fraction into
final states and yield for a given final state (given by underlying theory, i.e.
supersymmetry, Extra Dimensions, Inert Higgs etc,etc).
 Analysis optimized for given signature (mostly sensitive to cross-section,
mass and (less so) branching fractions)
Parameters of
interest
• Astrophysical part
– (Density of DM particles)2, diffusion (charged cosmic rays ), absorption
(gamma-rays from extragalactic sources)
 Where to look for the signal?
Nuisance parameters
> order of magnitude uncertainties
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Satellite:
Ground:
Pair production (>10 MeV)
Cherenkov radiation (> 20 GeV)
1.5 metres
10 000 metres
g
γ
γ
e
+
e–
2 metres
100 metres
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Gamma-rays: sensitvitiy overview
Large
FOV
 (E ) ~ 10%
Fermi:
Water
Cherenkov
 (E ) ~ 100%
IACTs:
angular
resolution (0.10)
CTA/CTA-US 2018
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The Fermi Large Area Telescope (Fermi-LAT)
g
e e–
+
• LAT
– 300 scientists from 6 countries
– Silicon tracker, interleaved with
tungsten
– CsI(Tl) Calorimeter
– Scans whole sky every three
hours
11. June2008
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Air Cherenkov Telescopes (2011)
4x12m IACTs, Crab sensitivity ~36 σ/√hr
VERITAS
2x17m IACTs ~ 19 σ/√hr
MAGIC
4x12m IACTs, Crab sensitivity ~43 σ/√hr (est)
HESS
All instruments have similar light collection area and have a “peak energy” of
around 80-120 GeV (trigger level) but ~300 GeV after typical tight analysis cuts
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First light for worlds largest Cherenkov
Telescope: HESS II, Summer 2012
28 meter diameter
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Targets and publications (incomplete)
Galactic
Centre
Fermi-LAT: TeVPA 2009, arXiv:0912.3828
Fermi: Goodenough & Hooper, arXiv:0910.2998
Fermi: Dobler et al., arXiv:0910.4583
Dwarf
galaxies,
Dark
Satellites,
Galaxy
Clusters
Fermi-LAT: Phys. Rev. Lett. 107, 241302 (2011)
H.E.S.S.: Astropart.Phys. 34 (2011) 608-616
MAGIC: Astrophys.J. 697 (2009) 1299-1304
VERITAS: Astrophys.J. 720 (2010) 1174-1180 .
VERITAS: Phys.Rev.D85:062001,2012
Galactic
diffuse
H.E.S.S. Phys.Rev.Lett. 106 (2011) 161301
Fermi: Cirelli et. al. arXIv: 0912.0663
Fermi-LAT: arXiv: 1205.6474
Extra
Galactic
Diffuse
Fermi-LAT: JCAP 1004:014,2010
Fermi: Akorvazian et. al.arXiv:1002.3820
Fermi : Huetsi et. al. arXiv:1004.2036
Lines
Fermi-LAT: Phys.Rev.Lett.104:091302,2010
Fermi: Vertongen et al. JCAP 1105 (2011) 027
Fermi: Weniger et al. arXiv:1204.2797
Fermi: Bringmann et al. arXiv:1203.1312
Fermi-LAT: 1205.2739, Phys.Rev.D.
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Targets and publications (incomplete)
Galactic
Centre
Strongest signal expected, most difficult background
Hard sources, not well understood diffuse emission, no
useful constraint published so far
Dwarf
galaxies,
Dark
Satellites,
Galaxy
Clusters
Dwarfs: weak signal, but relatively well controlled Dark
Matter Distribution and essentially no background (if at
high latitude).
Clusters: DM density not well constrained, but provides
boost factor (extended emission), so good for discovery (if
lucky)
Galactic
diffuse
Fermi-LAT: spatial and spectral discrimination, good
statititstics, extreme freedom in galactic diffuse emission.
IACT: best potential, small systematics due to diffuse
emission, ~100 hour observation time (GC halo)
Extra
Galactic
Diffuse
Very model dependent, good as target for spatial analysis.
Lines
Smoking gun*, got to get lucky.
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Dwarf galaxies probed in gamma-rays
Fermi
H.E.S.S.
MAGIC
Veritas
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Dwarfs galaxies – cleanest target
•
•
•
•
DM dominated (M/L ~10--1000).
Nearby (~ 100 kpc)
Low background but relatively small signal
Stellar velocities can be used to measure DM density (error
can be propagated to particle constraints)
e.g:
Charbonnier+, MNRAS 418 (2011)
1526
Strigari+,Phys. Rev. D, 75, 083526
Evans+, Phys. Rev., D69, 123501,
(2004)
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Analysis details
Fermi
Exposure
Background
(hours)
modeling
11 month,
Diffuse/
24 month
Point sources
DM distribution
Empirical NFW
(~ 1500 h)
H.E.S.S.
~15
On-off
Empirical NFW
Theo. NFW
VERITAS
~15
On-off
~50 (Segue)
MAGIC
~15
Empirical NFW
Empirical Einasto
On-off
Empir. NFW
Empir. core/cusp
Kazantzidis
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The new Fermi-LAT dwarf analysis
Fermi-LAT: Phys. Rev. Lett. 107, 241302 (2011)
• Combining single source
likelihoods
– less sensitive to individual source
fluctuations, improved constraints,
but analysis can be optimized
individually
• For the first time, including
uncertainties in DM density
– Applied to a the combination 
over-all result is much less affected
by the DM density uncertainties
(impact reduced by factor 10).
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Results (2 years)
4 year limits with more accurate response function have been
presented at the Fermi symposium
A. Drlica-Wagner (Fermi-LAT),
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Dwarf constraints -status
χχ  qq
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Galactic diffuse emission: Best shot for Air
Cherenkov telescopes
DM signal
Galactic diffuse emission
 Large signal (shape and spectrum)
 Large background
 Very complicated background for the Fermi-LAT
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Galactic diffuse emission: hard for Fermi-LAT
To some:
To Fermi-LAT DM hunters::
Diffusion
reacceleration
convection
energy loss
Radiation field
spallation
decay
B-field
B-field
CNO
Gas
e
p
DM
 π0  γγ
 π±  e±
Gas
p-bar,
 π±  e±
 π0  γγ
 Li, B 
Conventional diffuse emission: Fermi-LAT , Astrophys.J. 750 (2012) 3 (88 pages)
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Methodology
• Numerical solve Fokker-Planck-Kolmogorov equation
(GALPROP)
• 14 linear, 7 non-linear parameters, partly constrained
from independent (cosmic ray) observations + source
distribution
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Signal region and fitting
• Signal region:
Remove problematic regions
Choose signal region where DM profile
relatively unimportant.
• Fitting: spatial and spectral fit, treat linear and non linear
parameters as nuisance parameters in a profile likelihood
fit
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Results
• As tight limits as dwarf analysis, but different (and larger)
systematics
Fermi-LAT: arXiv: 1205.6474, accepted by ApJ
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H.E.S.S. Galactic Center Halo
• Galactic center is observed anyway
• 112 hours of GC observations
• Little diffuse background, sensitive to
gradients “only”
BG
Signal
5 deg
Signal
BG
LAT
Draco
11
month
Abramowski et al, PRL 106 (2011) 161301
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Gamma-ray constraints, present status
χχ  qq
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Cherenkov Telescope Array (CTA)
• Next generation Air Cherenkov telescope
• Increased sensitivity by factor 10  new insights for Dark matter,
Cosmic rays etc. etc.
• Global consortium: ~25 countries, ~500 scientists
• Construction start 2014, *full* operation 2018
24 m
12 m H.E.S.S.
7m
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Dark Matter scoping study
• Right now: optimization of array configuration
• DM targets studied:
–
–
–
–
Galactic Centre Halo
Dwarf Galaxies
Clusters of Galaxies
Spatial signal/Axions
arxiv:1208.5356
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Future Gamma-ray constraints – with CTA
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”Detections”
GeV WIMPs
~
MeV WIMPs
~
TeV WIMPs
~
2012!
From Bergström, Ann.Phys. (Berlin) 524, (2012)
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A line in Fermi-LAT data?
“If […] true, it would dwarf the Higgs boson discovery,“
Particle Physics blogger Jester
• 3.3σ LEE corrected (~50 events)
Bringmann+, arXiv:1203.1312
Weniger arXiv:1204.2797
• 5σ LEE corrected, and two lines?
Su&Finkbeiner, arXiv:1206.1616
also:Boyarski+, arXiv:1205.4700
Tempel+, arXiv:1205.4882 (4.5σ)
Signal 1.5 deg offset
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First Fermi-LAT line result: 2010
• Based on 11 month of data
• Similar analysis method, no
optimisation.
Fermi-LAT: Phys.Rev.Lett. 104 (2010)
091302
T. Ylinen, PhD
Thesis, KTH
Stockholm, 2010
Updated to 2 years data in:
Fermi-LAT: 1205.2739, Phys.Rev.D.
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Intriguing details 1: spatial distribution of GC
signal
Bringmann, Weniger,arXiv:1208.5481
Error bars correct?
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Intriguing details 2: Galaxy clusters?
Hektor+, arXiv:1207.4466v2
18 Galaxy clusters, 5 deg ROI
ROI optimisation?
Some redistribution going on?
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What says Fermi-LAT
(Fermi symposium, Nov 2, 2012
http://fermi.gsfc.nasa.gov/science/mtgs/symposia/2012/
A. Albert (Fermi-LAT)
• Nada
• 2.2σ @135 GeV (P7 data reprocessed  shift in energy)
• Publication to be submitted by the end of the year
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However, galactic centre
• 3.35σ (local, no look elsewhere effect)
A. Albert (Fermi-LAT)
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But …… limb signal!!
Excellent control region for (not only) line
searches, expected to be featureless
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Other control regions: nada!
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Questions to be answered before booking the trip to
Stockholm
• Is it instrumental, a fluke or physics?
– What is the (sufficiently strong) line signal in the Fermi-LAT Earth Limb
emission?
– Hard unexpected source at the GC?
– Can it be a background contamination, i.e. protons leaking through.?
– Can it be a problem in the estimated photon –efficiency ?
• If it is physics, is it dark matter?
– Why do Su+Finkbeiner find an offset?  could be explained incl. Baryons
M. Kuhlen+, 1208.4844
– Can it be a non-line spectral feature?  it is very line-like
– Can other physical processes except DM produce the feature  none has come
up with a convincing proposal
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SUSY in trouble?
• Light sleptons might still work ……
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My take on it today ….
• The true significance of this result is somehwere between
2.5σ and 5σ  so not quite a discovery by particle physics
standards.
• In favour: the feature fulfills amazingly many properties of a
DM induced signal, if analyses taken at face value.
• It’s too good to be true, and therefore not true?
• Fermi-LAT checks are not conclusive, but there are several
detected effects (at the right energy) which could be
problematic.
• So today, I do (do not) believe it is Dark Matter.
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Line outlook
• More Fermi-LAT data needed on GC and on Limb
– multivariate analysis of the signal essentially impossible
– Answer to the question, if this can be instrumental within next year (my
guess)
• If real: 5σ by 2016 (rough estimate) from Fermi-LAT in present
exposure conditions.
• Competition by HESS II (on line and capable of 5σ within 50 h
of GC observation).
Bergström, Bertone, JC, Farnier,
Weniger , arXiv:1207.6773 , JCAP
accepted
• GAMMA-400 (2018), DAMPE (China) (2015?)
Take a vote!
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DMA
Presentday limit
Next
generation
limit
Direct detection cross section (pb)
Direct detection, neutrinos (Sun)
Complementarity (Direct/Indirect)
CTA
FERMI
pMSSM
Some LHC detectable
Gamma-ray flux
Gamma-rays
Bringmann+, Phys.Rev. D83 (2011) 045024
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Complementarity with LHC
Just today 2 papers on the arxiv: Altmannshofer+, Cahill-Rowley+
Below: pMSSM (benchmark from coannihilation region)
LHC
solution:
NOT DM
LHC
solution:
DM
Empty contours: LHC only
Gaugino
masses
Excluded
with FermiLAT dwarf
limit
Bertone+,Phys.Rev. D85 (2012) 055014
Filled: Including Fermi
dSph Result
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Final remarks and summary
• Gamma-rays are the ”golden probe” for indirect detection.
• Most robust gamma-ray WIMP searches …..
– Lower masses: Dwarf spheroidal galaxies: Fermi-LAT
– Higher massesGalactic Center halo (H.E.S.S.).
• Gamma-ray searches have constrained the benchmark crosssection of ~10-26 cm-3 s, for WIMPs < 30 GeV, with a
robust and clean method .
• … at the same time yielding ”indications” worth to explore
experimentally ….
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Conclusions con’t
• Orthogonality to direct/neutrinos and LHC in the most
commonly studied theoretical scenarios (Supersymmetry).
– acc: LHC results, direct: Xenon 1t, IceCube results ..
• In 2019: CTA/Fermi-LAT constrain thermal WIMP x-sec
from 10 GeV – 10 TeV.  Endgame for the WIMP?
• … unless of course we get lucky …
–
nature picks a model with large line cross-section  Galactic Centre
• New players: Gamma-400 (2018), DAMPE (2015), HESSII
– nature introduces large enough substructure boost in clusters of galaxies 
Galactic clusters
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