1. Imaging Dark Matter with the Pamela Experiment
Mark Pearce
KTH, Stockholm
Mirko Boezio
University of Trieste
(Representing the Pamela Collaboration)
Mark Pearce - KTH Stockholm -

2. Galactic Rotation Curves
Interpret variation in red-shift across galaxy as a velocity distribution.
Newtonian prediction  expect velocity to fall across the galactic disk as mass density falls.
BUT observed rotational curves not consistent with visible distribution of matter.
Supports the view that galaxies are immersed in a halo of so-called dark matter.
Dark  neither radiates nor absorbs radiation.
Appears to make up ~90% of mass in the Universe
(M33 Spiral Galaxy)
[L. Bergström - hep-ph/ ]
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3. Candidates for Galactic Dark Matter
Massive Compact Halo Objects (MACHOs)
Low (sub-solar) mass stars. Standard baryonic composition.
Use gravity microlensing to study.
Could possibly account for 25% to 50% of Galactic Dark Matter.
Neutrinos
Small contribution if atmospheric neutrino results are correct, since mn < 1eV.
Large scale galactic structure hard to reconcile with neutrino dominated dark matter
Weakly Interacting Massive Particles (WIMPs)
Non-Standard Model particles, ie: supersymmetric neutralinos, c0.
Heavy (>10GeV) neutrinos from extended gauge theories. ~
Mark Pearce - KTH Stockholm -
Explore the use of neutralino decays as a probe to image dark matter in this presentation.

4. Mark Pearce - KTH Stockholm -
Neutralino WIMPs
Assume present in the galactic halo
is its own antiparticle  can annihilate in galactic halo
Antimatter not produced in large quantities through standard processes (secondary production through p + p  p + X)
So, any extra contribution from exotic sources ( annihilation) is an interesting signature
ie:  p + X
Produced from (e.g.)  q / g / gauge boson / Higgs boson and subsequent decay and/or hadronisation.
Rigorous discussion: L. Bergström et al. astro-ph/ c0 ~ -
Mark Pearce - KTH Stockholm -

5. Signature of Neutralino Annihilations
Distortion of antiproton flux due to one possible model of neutralino annihilation based on MSSM
This model predicts signal for large E(p)  high mass neutralino (~1 TeV).
Note that signal >> background for E(p)  20GeV
Need to perform an experiment accumulate a high purity sample anti-protons - -
Contribution from neutralino annihilation [P. Ullio, astro-ph/ ]
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Secondary production (background!)

6. An Overview of Pamela Time of flight system
Transition Radiation Detector
Anticoincidence system
Silicon Tracker
1.2 m
EM Calorimeter
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Permanent magnet

7. Mark Pearce - KTH Stockholm -
The Pamela Mission
Launch early 2003 onboard Resurs - Arktika no. 5 satellite.
Bari, Florence, KTH, Moscow, NASA/GSFC, NMSU, Rome, Siegen, Trieste.
Circular sun-synchronous polar orbit (98o) at 690km
>3 year mission
Total mass = 380kg / 345W power budget
Pamela housed in pressure compartment. Dry nitrogen atmosphere.
1 (active) + 1 (reserve) Gbyte mass memory.
Dedicated telemetry down-link (1Gbyte per day)
NB: Pamela is a general purpose experiment!
(e±, p, HC) spectra, He search
Polar orbit  can study low energy particles
Pamela Location
Mark Pearce - KTH Stockholm -
(-) -

8. Mark Pearce - KTH Stockholm -
Pamela Subdetectors
Anticoincidence system
Defines acceptance for tracker
Plastic scintillator + PMT
Binary read-out
TRD
Threshold device. Signal from e±, no signal from p, p
9 planes of Xe/Co2 filled straws (4mm diameter). Interspersed with carbon fibre radiators  crude tracking.
Aim: 102 separation e -vs- p (above 1GeV/c). NB: 106 with calorimeter.
Time-of-flight
Gives L1 trigger / detects albedos / particle identification (up to 1GeV/c) / dE/dx
Plastic scintillator + PMT
Timing resolution = 70ps
Si Tracker + magnet
Measures rigidity
5 Nd-B-Fe magnet segments (0.4T)
6 planes of 300mm thick Si detectors
~3mm resolution in bending view demonstrated, ie: MDR = 740GV/c
Si-W Calorimeter
Measures energies of e±. DE/E = 15% / E1/2.
Si-X / W / Si-Y structure.
22 Si / 21 W  16X0 / 0.9l0
Imaging: EM - vs- hadronic discrimination. Reconstruct long. and transverse shower profile.
Mark Pearce - KTH Stockholm -
[Acceptance ~21 cm2sr]

9. Mark Pearce - KTH Stockholm -+
Separating p from e
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10. Detecting p with Pamela-
Detecting p with Pamela
10GeV e- -
10GeV p
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11. Mark Pearce - KTH Stockholm -
Calorimeter Response
Mark Pearce - KTH Stockholm - -
10GeV e-
10GeV p

12. Summary and Conclusions
Neutralinos are a promising candidate for WIMP dark matter
Neutralinos can annihilate in the galactic halo ...
… this could give rise to high energy (> 10GeV) antiproton signature
Pamela experiment is designed to measure antiproton spectrum from 80MeV to 190MeV.
>3 year mission  large event samples
Combination of TRD + Si tracker + imaging Si-W calo + TOF (trigger) and anticoincidence  can isolate a pure sample of antiprotons.
Engineering model currently under construction.
Flight model due 2Q 2002.
Launch 1Q 2003.
Mark Pearce - KTH Stockholm -