Transcript Results From VERITAS K. Byrum High Energy Physics (HEP) Division Argonne National Laboratory Indirect and Direct Detection of Dark Matter 6-12 Feb 2011, Aspen Colorado.

Results From VERITAS
K. Byrum
High Energy Physics (HEP) Division
Argonne National Laboratory
Indirect and Direct Detection of Dark Matter
6-12 Feb 2011, Aspen Colorado
Talk Outline
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Introduction
VERITAS
VERITAS Results
VERITAS Upgrade
Beyond VERITAS: CTA
Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
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Very High Energy Gamma-ray Sky
1999
Crab first observed
1989 (Whipple)
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Very High Energy Gamma-ray Sky 2010
>130 sources
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Very High Energy Gamma-Ray Science:
Astronomy, Astrophysics, Cosmology, Fundamental Physics
Search for Dark Matter & Fundamental Physics
Extragalactic Science (GRBs, Cosmology, AGNs, Starburst Galaxies)
Galactic Science (SNRs, PWNs, Binaries)
This is a Broad
Program
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Current status: Very High Energy
Gamma-ray Detectors
FGST
HAWC
Milgro
(future)
MAGIC
VERITAS
H.E.S.S.
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Talk Outline
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Introduction
VERITAS
VERITAS Results
VERITAS Upgrade
Beyond VERITAS: CTA
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VERITAS
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VHE Gamma-ray Technique
Multiple Telescopes:
 improve angular resolution
 improve energy resolution
 reduce background
 eliminate muons
 improve stability
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VERITAS is currently the most sensitive TeV Observatory in the world.
500 MS/s Flash-ADC on
every ch. 8-bit dual gain
Trigger & Readout: Three-level trigger
 Constant fraction discriminator for each PMT
 Pattern trigger on every telescope (requires hits
on adjacent 3 PMTs within ~7-9ns)
 Array trigger requires 2 or more telescopes
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Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
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Talk Outline





Introduction
VERITAS
VERITAS Results
VERITAS Upgrade
Beyond VERITAS: CTA
Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
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VERITAS: Indirect Dark Matter Program
Dark Matter makes up ~25% of energy budget of
Universe
WDMh2 = 0.113 (WMAP +BAO +SN1a) ~ 23%
DM has only been inferred gravitationally by its
interaction with visible matter
Well described theoretically by extensions to standard
model of particle physics (MSSM, Kaluza-Klein).
Cosmological constraints: Thermal relic of early universe
with weak scale cross section & mass produces present
DM density (Lee & Weinberg, 1977)
 ~ 50 GeV/c2 < MWIMP < ~ 10 TeV/c2
WIMP annihilation to g-rays:
g-ray line from direct annihilation (higher order
process)
g-ray continuum from hadronization
Enhanced near MWIMP from internal brem
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Search for Indirect Detection of Dark Matter
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VERITAS Dark Matter Program
• Concentrate on WIMP scenario: SUSY or Kaluza-Klein particle with mass in the GeV-TeV range
• Assume pair annihilation giving rise to flux of g-rays w/cutoff at Mwimp
• Expect g-ray flux proportional to squared DM density
Because of large uncertainties (WIMP mass, s, astrophysical flux),
VERITAS observing strategy has been: “variety of targets”
Target
Galactic Center
Dwarf spheroidal
galaxies
Globular clusters
Disadvantages
Advantages
-Closeby
-Many astrophysical backgrounds
-Huge amount of DM
-Huge uncertainities in the DM
distribution (O(103))
-DM dominated
-May be beyond reach of current
instrument sensitivity
-Clear of astrophysical
bkgd
-Very close
-Can be tidally disrupted: uncertainties
in the DM distribution O(10))
-Not DM dominated
-Astrophysical backgorund
-Interplay of baryons with DM not well known
Clusters of galaxies
-Huge amount of DM
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-Very far
-Astrophysical background
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Indirect DM Search using Dwarf Spheroid
• Recent
discovery of many dSphs by
SDSS; likely more discoveries in future
VERITAS Dwarf Spheroid Targets:
Draco, Ursa Minor, Bootes 1,
Willman 1, Segue 1
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Indirect DM Search using Dwarf Spheroid
Dwarf galaxy observations made since early 2007
Wobble pointing mode (0.5deg offset from camera center).
Second moment analysis (Hillas parameter of the shower image in the camera
focal plane) for the selection of g-rays: cut optimized for a 3.5% Crab-like
source
Reflected background model to subtract the residual background
Typical map of
null observation
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Indirect DM Search using Dwarf Spheroid
No significant excess detected in any of
the observations.
aSignificance
calculated using Li & Ma method (ApJ 272, 317 eqn.17)
b95%
CL upper limits using Rolke, Lopez & Conrad (arXiv:0403059v4)
bounded profile likelihood method
cAbove
energy threshold, for a Crab-like spectrum
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Indirect DM Search using Dwarf Spheroid
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Indirect DM Search using Dwarf Spheroid
MSSM models from DarkSUSY within ±1 standard
deviations of WMAP measured relic density.
 Uncertainty ±1 order of magnitude due to
systematics in halo modeling
ApJ 2010
X 100
95% CL upper limits from Reflected Region
Background Model analysis and Rolke zero-bounded
profile likelihood
Boost factor from substructure, internal
bremsstrahlung could give ×10-100 smaller <σv>
Limits from VERITAS
on annihilation
<sv>: ~ 10-23 cm-3 s-1
By Matthieu Vivier
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VERITAS Future Dark Matter Analysis
 Continued observations on dSphs should reduce the
theoretical uncertainties on mass models.
 Will target deeper exposures on select dSph targets
 Stacked analysis
 FERMI follow-up observations of DM source candidates
 Analysis currently underway
– Galactic Center
– Globular clusters
– Electron spectrum
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Talk Outline





Introduction
VERITAS
VERITAS Results
VERITAS Upgrade
Beyond VERITAS: CTA
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VERITAS Upgrade Underway
Motivation
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Result is Improved Sensitivity
Increased effective area
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Better Background Suppression
Better Angular Resolution
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Lower Energy Threshold
Faster Slewing time
Faster detection for a given source
strength
Detect weaker and more distant
sources
Components (started with T1
move in Summer 2009)
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PMT replacement with higher QE PMTs
FPGA Level-2 pattern Trigger
Faster slewing for Telescopes
After T1 move + mirror align
1% crab = 28 hr (already)
After Trigger, High QE PMTs:
1% crab: ?
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Higher QE PMTs
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VERITAS FPGA Level 2 Trigger Upgrade
 Meant to be a drop in replacement to current aging L2
 With enhanced capabilities
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Coincidence window improvement (down to 3-4ns)
Pixel timing alignment
Improved diagnostic capabilities
Reconfigurable trigger through downloadable firmware
Updates/improvements do not require access to hardware
Alternate/experimental triggers may be tested w/o access to hardware
 All the hooks in place for adding a future L4
topological trigger
First telescope installed parasitically Nov
2010; remaining telescopes in Summer
2011.
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Talk Outline





Introduction
VERITAS
VERITAS Results
VERITAS Upgrade
Beyond VERITAS: CTA
Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
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CTA
Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
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VHE Gamma-ray Sensitivities: Present and Future
FGST
Energy (GeV)
Space
IACT
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EAS
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Sensitivities for WIMP detection
x100 Exposure
x10 Sensitivity
x5 BG reduction
E Threshold
 “A significant region of parameter space could potentially be excluded (or the
effort might result in a detection!) through observations of nearby dwarf galaxies.
Therefore, increasing the sensitivity of atmospheric Cherenkov telescopes by
another order of magnitude is our top priority for exploring the nature of dark
matter” (Astro2010, Panel Report)
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Summary
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VERITAS: Broad science program (that I didn’t discuss)
Current Dark Matter program :
– Observations of 5 northern dSphs, with exposures 15 hrs
– No g-ray signal detected (so far)
– Limits on annihilation cross-sections of order 10-23-10-24 cm3 s-1; competitive
with limits obtained by MAGIC and with southern dSphs by HESS
– Results using Draco, Ursa Minor, Willman 1 and Bootes 1 reported in ApJ
– Analysis of Galactic Center and Globular clusters underway
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VERITAS upgrade underway; expect improved sensitivity
Future Dark Matter observations w/VERITAS:
– Upcoming observational data sets on dSphs will reduce the theoretical
uncertainties on mass models and point to better dSph candidates
– Will target deeper exposures on select targets
– Will provided FERMI follow-up observations of DM source candidates
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Future Dark Matter observations with CTA
– Improved sensitivity of CTA order of magnitude beyond current instruments
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