1. KIPAC-SLAC, Stanford University
The Search for Dark Matter Using the Gamma Ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT)
Ping Wang
KIPAC-SLAC, Stanford University
Representing GLAST LAT Collaboration Dark Matter and New Physics Working Group
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2. Overview What is GLAST LAT?
How dose dark matter shine in the gamma ray sky?
Where should we look for dark matter with GLAST?
Summary
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3. GLAST LAT Collaboration
France
IN2P3, CEA/Saclay
Italy
INFN, ASI
Japan
Hiroshima University
ISAS, RIKEN
United States
California State University at Sonoma
University of California at Santa Cruz - Santa Cruz Institute of Particle Physics
Goddard Space Flight Center – Laboratory for High Energy Astrophysics
Naval Research Laboratory
Ohio State University
Stanford University (SLAC and HEPL/Physics)
University of Washington
Washington University, St. Louis
Sweden
Royal Institute of Technology (KTH)
Stockholm University
Principal Investigator:
Peter Michelson (Stanford & SLAC)
~225 Members
(includes ~80 Affiliated Scientists, 23 Postdocs,
and 32 Graduate Students)
Cooperation between NASA and DOE,
with key international contributions from
France, Italy, Japan and Sweden.
LAT Managed at
Stanford Linear Accelerator Center (SLAC)
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4. GLAST is a NASA Mission Large Area Telescope (LAT)
Launch: September 2007
Lifetime: 5-years (10-years goal)
Orbit: 565 km, circular
Inclination: 28.5o
Large Area Telescope (LAT)
20 MeV GeV
GLAST is the next generation after EGRET… factor > 30 improvement in sensitivity
Large effective area, factor > 5 better than EGRET
Field of View ~20% of sky, factor 4 greater than EGRET
Point Spread function factor > 3 better than EGRET for E>1 GeV. On axis >10 GeV, 68% containment < 0.12 degrees
Minimize rejection of E>10GeV gamma rays due to backscatter into cosmic ray shield
No expendables (EGRET had spark chamber gas) - long mission without degradation (5-10 years) OK
GLAST Burst Monitor (GBM)
8 keV - 30 MeV
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5. GLAST Large Area Telescope (LAT) 20 MeV – 300 GeV
Anti-Coincidence Detector
4% R.L.
89 scintillating tiles
efficiency (>0.9997) for MIPs 
1.8 m
Tracking detector
16 tungsten foils
(12x3%R.L.,4x18%R.L.)
18 pairs of silicon strip arrays
strips (228 micron pitch) e+ e–
1.0 m
Calorimeter
8.5 radiation lengths
8 layers cesium iodide logs
1536 logs total (1200kg)
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6. Indirect detection – a complementary way to observe dark matter signals!
DM Experiment Class
Dark matter source location
Dark matter interaction
Direct Detection
Earth’s Surface
WIMP-nucleus scattering
Particle Beam Collider
Irrelevant
WIMP pair production
Indirect Detection
Earth, Sun, Galaxy, extragalactic
WIMP pair annihilation OK
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7. WIMP annihilation: continuum spectrum
Dominant mode for Majorana fermion WIMPs: g
time p0 g c
W-/Z/q } nm
nmne p+ m+ e+ _ nm c
W+/Z /q
nmne p- m- e-
+ a few p/p, d/d
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8. WIMP annihilation: continuum spectrum
Additional dominant mode for Dirac fermion or boson WIMPs: p0 g t- nt p- nm m-
nmne e-
time
nm/tne c
n/e-/m-/t- }
m/t- e- or
nm/tne
n/e+/m+/t+ c
m/t+ e+
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9. WIMP annihilation: spectral lines
For gg lines, energy = WIMP mass; branching fraction is suppressed
e+e-, nn lines are possible at tree level; but suppressed for Majorana fermions
For WIMP masses > MZ /2 can also have gZ0 line
Measurement of line branching fractions would constrain particle theory
time
g,e+,n c ? c
g,e-,n c γ Z0 ?
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10. WIMP annihilation: gamma-ray flux
Photon flux from WIMP annihilation:
Ann. Cross-section
(cosmology, particle phys)
Ann. Spectrum
(particle physics)
WIMP number density ^2
(astrophysics, particle phys)
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11. WIMP annihilation: gamma-ray yield
Gamma ray yield per final state bb
MWIMP
Total# g
>100MeV
>1GeV
>10GeV
10 GeV
17.3
12.6
1.0
100GeV
24.5
22.5
12.4
1TeV
31.0
29.3
22.4
12.3
200GeV mass WIMP
WIMP pair annihilation gamma spectrum
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12. Dark Matter in the gamma ray sky
Milky Way Halo simulated by Taylor & Babul (2005)
All-sky map of DM gamma ray emission (Baltz 2006)
Galactic center
Milky Way satellites
Milky Way halo
Extragalactic
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13. Diffuse gamma ray background
EGRET Eg>1GeV, point-source subtracted, Cillis & Hartman (2005)
Modeling with GALPROP
Inputs include matter distribution
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14. Galactic satellites – seen and… unseen?
Moore, et.al. (1999)
(M=5x1014Msun, R=2000kpc)
(M=2x1012Msun, R=300kpc)
Should be ~500 satellites w/ M>107Msun…
Where are they?
(Galaxies within Virgo)
visible
satellites (faint)
Look up paper by speaker Naoki Yoshida; add summary on low surface brightness objects and reference
V=(GMbound/Rbound)0.5
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15. Simulation Example: DM Satellite
55-days GLAST in-orbit counts map (E>1GeV)
Galactic
Center
Optimistic case: 70 counts signal, 43 counts background within 1.5 deg of clump center
30-deg
latitude
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16. DM satellite energy spectrum
E-2.6 spectrum
Dark matter spectrum
Diffuse background
GLAST 55 days (10-sigma)
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17. Observable DM satellites (estimate)
Simulation of Milky Way dark matter satellites from Taylor & Babul, 2004, 2005
SUSY model benchmark definitions LCC# from Baltz, et al, 2006
Background estimate using EGRET above 1GeV (point-source subtracted) from Cillis & Hartman 2005
Signal, background flux inside the tidal radius
LCC2 and LCC4 are much more favorable to GLAST than LCC1 and LCC3
LSP WIMP (SUSY)
GLAST 5-yrs
LCC2
LCC4
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18. Summary
GLAST LAT offers a unique opportunity to discover WIMP dark matter by the gamma rays produced in pair annihilations
GLAST collaboration will search for WIMP annihilation gamma rays from galactic center, galactic halo, galactic satellites and extragalactic
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