The Physics of AMS02

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The Physics of AMS-02

• Francesca Spada INFN Rome
• on behalf of the AMS-02 Collaboration
• Plank07 - Warsaw

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• Precision Cosmology
• WMAP
• CMB spectrum
• SSDS 3D
• matter spectrum
• HUBBLE
• SuperNova Ia redshift

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• Several models provide CDM candidates (WIMPS)
• R-parity conserving Supersymmetric models
• Lightest SUSY particle
• neutralino ?
• Extra-dimensional models
• Lightest Kaluza-Klein particle
• n1 mode of U(1) gauge boson B(1)
• May be discovered at LCH?
• Difficult to correlate with CDM
• Part of the parameter space not accessible

Astrophysical WIMP detection is needed
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• Indirect search of CDM detection of WIMP
  annihilation products
• cc annihilations can produce
• Neutrinos
• direct production
• W decay
• Heavy Quarks decay
• charged Pions decay
• e
• direct production (strongly suppressed) Ee mX
• W decay
• Heavy Quarks decay
• Leptons and charged Pions decay
• Photons
• direct Production Eg mX
• decay of neutral Pions
• p
• No direct production
• Hadronization Eh ltlt mX

Channels accessible to AMS
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• 3 years on the ISS
• Superconducting magnet
• New detectors for multichannel approach
• ANTIMATTER SEARCH He/He ratio lt 10-9
• COSMIC RAY FLUXES up to Z26
• DARK MATTER SEARCH
• () ready for launch date

• Precursor flight
• 10 days on Space Shuttle Discovery
• limit on He/He ratio lt 1.110-6
• very nice measurements of primary and secondary
  p, p, e-, e, He, and D spectra from 1 to 200
  GeV
• (Phys. Rept. vol. 366/6 (2002) 331)

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The AMS-02 detector
TRD e/p separation
Electronics crates
TOF b, Z
RICH b, Z
Electromagnetic CALorimeter e/p separation, E
CRYOMAGNET and TRACKER Z, R
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Transition Radiation Detector (TRD)
Fleece radiator straw tubes (XeCO2) e/p
separation gt 102 up to 300 GeV 3D tracking
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Time of Flight (TOF)
22 layers of scintillators, Dt 160 ps Main
Trigger Z separation b with few precision
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Superconducting Magnet
Coils cooled to 1.8 K by 2.5 m3 of superfluid
He Contained dipolar field of 0.85 Tm2
First Superconducting Magnet ever operating in
Space!
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Silicon Tracker
8 layers double sided silicon microstrip
detector Z separation R up to 2-3 TeV sR lt 2
for R lt 10 GeV
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Ring Imaging Cherenkov (RICH)

• 2 Radiators NaF (center), Aerogel (elsewhere)
• Z and isotopes separation
• smass 2 below 10 GeV/n
• b with 0.1 precision

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Electromagnetic Calorimeter
9 superlayers of Lead Scint. Fibers Standalone
Trigger e?, ? detection sE lt3 for E gt 10 GeV
e/p separation gt 103 3D imaging
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AMS-02 Fluxes from Cosmic Rays

• Expected ratios
• e/p 510-4 _at_ 10 GeV
• e/e- 10-1 _at_ 10 GeV
• g (galactic center)/p 10-4 _at_ 10 GeV
• g (galactic center)/e- 10-2 _at_ 10 GeV
• p/p 10-4 _at_ 10 GeV
• p/e- 10-2 _at_ 10 GeV

AMS 1 s
Particle Energy range p 0.1 up to TeV p 0.5
to 300 GeV e- 0.1 up to TeV e 0.1 to 300
GeV He 1 up to TeV anti He, , C 1 up to
TeV Light Isotopes 1 to 10 GeV/nucleon ?
1 to TeV
AMS 1 hour
AMS 1 day
AMS 1 year
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Positrons

• An excess in the 10 GeV region has been reported
  by HEAT based on a 102 positrons sample
• AMS will collect about 105 positrons in the 10 lt
  E lt 50 GeV region, in 3 years
• Main background sources
• rel. abundance rejection factor
• protons 104 102 -103 TRD x 103 ECAL ³ 105
• electrons 10 104 TOFTracker

p
e
P.Maestro, PhD thesis, 2003
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Positrons
Possible neutralino scenarios Example of
neutralino annihiliation signals observed by AMS
with the boost factors that fit the HEAT data
and motivated with a inhomogenous dark matter
density (clumpiness)

• gaugino dominated
• mc 340 GeV, boost factor95
• e primarily from hadronization

• gaugino dominated
• mc 238 GeV, boost factor116.7
• hard e from direct gauge boson decay

Baltz et al., Ph.Rev D65, 063511
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Positrons
More neutralino scenarios boost factors The
mimimal boost factor to see the LSP annihilation
at 95 C.L. in the positron channel in 3 years is
reduced if the gauginos mass universality
condition in mSugra is relaxed

• Relaxing gaugino mass universality
• Gluino Mass M3 50 m1/2

• mSugra
• Mi (GUT) m1/2 i1,,3
• tan b 10

J. Pochon, PhD thesis, 2005
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Positrons

• Kaluza-Klein scenarios
• No suppression of the direct annihilation into
  ee- because the lightest KK is a boson
• Characteristic steep spectra from the hard
  direct production very different from the
• broad neutralino ones

J.Feng,Nucl.Phys.Proc.Suppl.134 (2004) 95
J Pochon P Salati
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Antiprotons
Main background sources rel.
abundance rejection factor protons 104 106
ToF, RICH, electrons 102 103 104
TRDEcal
Antiproton acceptance 1-16 GeV 0.160
m2sr 16-300 GeV 0.033 m2sr
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Antiprotons
Neutralino scenarios Large errors at low momentum
sensitive to details of CR propagation, C/B
ratio Low energy Spectrum is well explained by
secondary production. Expected signal at high
energy (10 300 GeV)

• AMS-02
• Conventional p flux
• Statistical errors (3 years)

Possible distorsions due to WIMPs (large boost
factor needed)
P. Ullio (astro-ph/9904086)
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Antiprotons
Neutralino scenarios AMS-02 measured
antiproton/proton ratio, some regions are not
accessible to LHC

• AMS-02 with M? 840 GeV

• AMS-02 with M? 206 GeV

• AMS-02 expected

• AMS-02 expected

Not accessible to LHC
P. Brun et al. (2006)
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Photons
The center of the galaxy can be a very intense
point-like source of g from dark matter
annihilations Unlike positrons, photons travel
long distances and point to their source
The annihilation signal could be enhanced by a
cuspy profile of the DM density at the galaxy
center (super-massive black holes, adiabatic
compression, ...)
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Photons

• Two g detection modes in AMS-02
• Photon conversion direction from Tracker, energy
  from TrackerEcal
• Single photon direction and angle from Ecal

Main bg d rays Rejection factor gt105(p),
4104(e) TRD veto, invariant mass
Main bg secondaries (p0) from p
interactions Rejection power 5106 veto on
hits, g direction
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Photons
Expected performance Resolutions and acceptance
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Photons

• Kaluza-Klein SuSy Models scan for different
  halo profiles
• Galactic center treated as point source
• NFW halo profiles (Navarro, Frenk White, ApJ
  490 (1997) 493)

A. Jacholkowska et al., Phys. Rev. D74, 023518
(2006)
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Conclusions

• The AMS experiment, during its 3 year mission,
  will be able to measure simultaneously and with
  unprecedented precision the rates and spectra of
  positrons, photons and antiprotons in the GeV-TeV
  range, looking for a Dark Matter annihilation
  signal.
• confirm or disprove with high accuracy the excess
  in HEAT positron data in the few GeV region
• a ? signal from the galactic center will be
  visible in AMS in the case of cuspy halo profile
  or extra enhancements
• very accurate measurement of the high energy
  tail of the antiproton spectrum
• The AMS simultaneous measurements of other
  fundamental quantities (p and e- spectra, B/C
  ratio) will help to disentangle purely
  astrophysical effects from true dark matter
  signals.
• Several models for Dark Matter candidates can be
  constrained by the new AMS data.
• End of 2008, AMS-02 will be ready at NASA KSC for
  the launch to the ISS

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Photons
AMS-02 exposure to the galactic center
Single photon mode (geom. acc.) GC 15 days
Conversion mode (sel. acc.) GC 40 days