Indirect

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Indirect Dark Matter Search with AMS-02
Stefano Di Falco INFN Universita di Pisa for
the AMS collaboration
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Indirect search for Dark Matter
Photons Direct Production Eg mX Decay of
Neutral Pions
AMS a multichannel approach
ee- Direct production Ee mX Decay of W,
Decay of Heavy Quark Decay of Leptons and
Charged Pions
pp, (dd) No direct production Hadronization Eh
ltlt mX
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The AMS (Alpha Magnetic Spectrometer) experiment
AMS-01
AMS-02

• 1998
• 10 days on Space Shuttle Discovery
• - He/He 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)

• 2008-
• 3 years on ISS
• - Superconducting magnet
• New detectors
• ANTIMATTER SEARCH He/He lt 10-9
• COSMIC RAY FLUXES up to Z26
• DARK MATTER SEARCH

ready for launch date
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The AMS detector
TRD (Transition Radiation Detector) 20 layers of
Foam Straw Drift Tubes (Xe/CO2 ) 3D tracks, e/h
separationgt102 rej. up to 300 GeV
1 m
2 m AMS Weight 7 Tons
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The AMS detector
TOF (Time of Flight) 22 layers of
scintillators, Dt 160ps Trigger, Z separation,
b with few precision
1 m
2 out of 4 layers
2 m
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The AMS detector
Superconducting Magnet 12 racetrack coils 2
dipole coils cooled to 1.8 K by 2.5 m3 of
superfluid He Contained dipolar field BL2 0.85
Tm2
1 m
Technological challenge first superconducting
magnet operating in space
2 m
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The AMS detector
Tracker 8 layers double sided silicon microstrip
detector sR(igidity)lt2 for Rlt10 GV, R up to 2-3
TV, Z separ.
1 m
2 m
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The AMS detector
RICH (Ring Imaging CHerenkov) 2 Radiators NaF
(center), Aerogel(elsewhere), b with 0.1
precision, Z and isotopes separation, (2
precision on mass below 10 GeV/n)
1 m
2 m
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The AMS detector
ECAL (Electromagnetic Calorimeter) Sampling 9
superlayers of LeadScint. Fibers trigger, e?, ?
detection sE(nergy) lt3 for Egt10 GeV, 3D
imaging e/h separationgt103 rej
1 m
2 m
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Expected particle fluxes
p and He from AMS-01 e, e- and g from Moskalenko
Strong
e/p 510-4 _at_ 10 GeV e/e- 10-1 _at_ 10 GeV
ggalactic center/p 10-4 _at_ 10 GeV ggalactic
center/e- 10-2 _at_ 10 GeV
Very high particle identification needed
ApJ 493 (1998) 694
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AMS response to positrons and protons
TRD signal
Positron
Proton
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AMS response to positrons and protons
TOF signal
Positron
Proton
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AMS response to positrons and protons
Tracker signal
Positron
Proton
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AMS response to positrons and protons
RICH signal
Positron
Proton
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AMS response to positrons and protons
ECAL signal
Positron
Proton
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AMS response to positrons and protons
ECALTracker E/p matching
Positron
Proton
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Positron and background acceptance
Results from a montecarlo study using
discriminant analysis
Kinetic energy (GeV)
Kinetic energy (GeV)
Acceptance for e 0.045 sr m2 from 3 to
300 GeV Rejection factor for p 105
Rejection factor for e- 104
P. Maestro, PhD Thesis, 2003
Including a 7 flux factor improvement because
ltEdepgtEkin/2 )
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Number of Positrons in 3 years
In 3 years AMS will collect O(105) e with 10ltElt
50 GeV O(102) for HEAT
Total contamination 4
Reconstructed energy (GeV)
Good sensitivity up to 300 GeV
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Positron fraction statistical error in 3 years
The positron fraction e/(ee-) is preferred to
the e flux because is less sensitive to
uncertainties on cosmic-ray propagation and solar
modulation
Parametrization of the standard prediction for
positron flux (without Dark Matter)
Errors are statistical only
Baltz et al., Phys. Rev. D 59, 023511
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Possible scenarios from neutralino annihiliation
Example of neutralino annihiliation signal
observed by AMS with the boost factors found by
Baltz et al. to 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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More neutralino scenarios needed 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 gaugino mass
universality condition in mSugra is relaxed

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

• mSugra
• m1/2 M1 M2 M3
• tan b 10

J. Pochon, PhD Thesis, 2005
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Possible positron signals from Kaluza-Klein model
Kaluza-Klein model are interesting because allow
for direct production of ee- pairs in the
annihilations of the LKP (B1)
Boost factors needed O(102) to fit HEAT
data 1?10 for discovery
much steeper raises can fit HEAT data

• AMS 3 years Signal with Boost adjusted on HEAT
  data Bg
• AMS (3 years) Signal with Boost at visibility
  limit Bg

Positron fraction e/(ee-)

• Background ( no DM)

J Pochon P Salati
J.Feng,Nucl.Phys.Proc.Suppl.134 (2004) 95
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Dark Matter annihilation into photons

• The center of the galaxy can be a very intense
  point-like source of gammas from dark matter
  annihilations.
• Unlike positrons, gammas travel long distances
  and point to the source

• The annihilation signal could be enhanced by a
  cuspy profile of the DM density at the galaxy
  center (super-massive black hole (SMBH),
  adiabatic compression,...)

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Photon detection in AMS
Photon conversion
Single Photon (direct measurement)
Direction (angle) from Tracker Energy from
Tracker (and ECAL)
Direction (angle) from ECAL Energy from ECAL
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Gamma energy and angular resolution
Energy resolution
6
3
1o
Angular resolution
0.02o
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Main backgrounds to Photons
Conversion mode
Single Photon mode
d rays Rejection factor gt105(p), 4104(e) Using
TRD veto, invariant mass
Secondaries (p0) from p interactions Rejection
power 5106 Using veto on hits, g direction
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Gamma acceptance and effective area
Acceptance (m2.sr)
GeV
Max Acceptance Conversion mode 0.06 m2sr
Single photon mode 0.097 m2sr
Field of view Conversion mode 43 Single
photon mode 23
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AMS-02 Exposure to g from galactic center
51º latitude
Revolution 90
Conversion mode (sel. acc.)
Single photon mode (geom. acc.)
GC 15 days
GC 40 days
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Statistical significance (single photon mode)
Statistical error on photon spectrum from
galactic center (AMS 3 years)
68 C.L.
95 C.L.
Good sensitivity between 3 and 300 GeV
F. Pilo, PhD Thesis, 2004
E (GeV)
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Gamma sensitivity to neutralino annihilation
Example m? 208 GeV (AMS 1 year)
Egret
E2Flux (GeV/cm2s)

• Background
• Signal
• Background Signal

• Background
• Signal
• Background Signal

E (GeV)
L. Girard. PhD Thesis,2004
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Gamma sensitivity for different halo profiles
Kaluza-Klein SuSy Models Scan for different
halo profiles
A. Jacholkowska et al., astro-ph/0508349
Navarro, Frenk White, ApJ 490 (1997) 493
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Antiproton detection in AMS

• Main Backgrounds
• Protons charge confusion, interactions with the
  detector and misreconstructed tracks.
• Electrons beta measurement, e/h rejection

Rejection p gt 106 (ToF, Rich ) e- gt
103-104 TRD /Ecal Acceptance 1-16 GeV
0.160 m2sr 16-300 GeV 0.033 m2sr
Antiproton signal -Single track in TRD
Tracker - Z -1
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Antiproton flux measurement with AMS
Current Measurements large errors below 35 GeV,
AMS-02
Conventional p flux with Statistical Errors (3
years) Range 0.1 to 500 GeV
V. Choutko (2001)
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Possible DM signal in Antiproton spectrum
Low Energy Spectrum well explained by secondary
production. There is room for a signal at high
energy (10 300 GeV)

• Mc964 GeV (x4200)
• Mc777 GeV (x1200)

However models require a boost factor.
P. Ullio (1999)
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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, gammas and antiprotons in the GeV-TeV
range, looking for an excess of events that could
hint for a dark matter annihilation
signal. Several models for dark matter
candidates can be constrained by the new AMS
data. The AMS simultaneous measurements of other
fundamental quantities (p and e spectra, B/C
ratio,) will help to refine the astrophysical
predictions enhancing the compelling evidence
for a dark matter signal.
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Backup
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Background flux calculations
F(m-2 s-1 sr-1 GeV-1) fbg fsignal
Local Background Flux determined by propagation
of CR yield per unit volume through simulation
(GALPROP)
Gas (HI,H2,HII) distribution
CR source distribution and spectrum (index,
abundances)
Diffusion model (reacceleration, diffusion) and
parameters (D,size h, cross-sections)

• Physical background
• Antimatter channels
• secondary products from cosmic ray spallation in
  the interstellar medium
• Gamma ray channel
• diffuse Galactic emission from cosmic ray
  interaction with gas (p0 production, inverse
  Compton, bremsstrahlung)

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Signal flux calculations
F(m-2 s-1 sr-1 GeV-1) fbg fsignal
Local Flux determined by propagation of CR yield
per unit volume through simulation (GALPROP)
(propagation model and parameters )
CR yield per unit volume (r,z,E)
gann(E).ltsvgt(??(r,z) /m?)2
gann(E) particle production rate per
annihilation
COSMOLOGY
ASTROPHYSICS
WMAP () constraints on ??h2
Rotational velocity measurements
m? neutralino mass
ltsvgt coannihilation cross-section
HEP
DM density profile shape ( boost factors)
Accelerator constraints
??(r,z) density distribution
SUSY parameter space (5)
Boost factors clumpiness,cuspiness, baryon
interaction, massive central black hole
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Indirect Search neutralino annihilation
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Indirect Search neutralino annihilation
Charged

• Propagation G
• diffusion model
• earth vicinity

• Cosmology
• Nominal Local density of Dark Matter 0.3 GeV/cm3
  
• Distribution
• Clumps lt?2 gt Boost lt?gt2
• Halo shape (Galactic Centre)

• Particle Physics
• models ?anni , annihilation channels and mX
• should be compatible with DM Relic Density

Gamma
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Antideuterons
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Antideuterons

• Antideuterons have never been measured in CR
• could be an alternative channel to look for dark
  matter signals. Claim almost
  background-free channel at low energies

DM signal
Spallation spectrum
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Antideuterons
Spallation spectrum
Estimate of AMS potential under study focused on
low momenta, antiproton flux is the main
background need 105 discrimination - mass
resolution is crucial!
tertiary component
TOA flux prediction is even less optimistic
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Some favourites Dark Matter candidates

• Models of Supersymmetry mSugra
• 5 parameters
• m0 scalar mass
• m1/2 gaugino mass
• A0 sleptons and squarks coupling
• tan ? ratio of VED of the Higgs doublets
• sign(?) Higgs mass parameter
• R-parity conservation
• Ligthest Susy Particle stable Neutralino
• Extensions ?à la Kaluza-Klein 2 working models
  with Extra Dimensions
• Universal Extra Dimensions (UED)
• all SM particles propagates in X-dimensions
• Lightest First Excitation Level is stable B(1)
  ( ?(1) )
• Warped Grand Unified Theories
• Z3 symmetry to ensure proton stability
• Lightest Z3 charged particle is stable (?R(1) )

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Positron fraction after 3 years AMS and PAMELA
AMS
PAMELA
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Antiproton expected flux (without DM)
Uncertainty mainly due to present determination
of B/C

• Low Energy Spectrum well explained by secondary
  production.
• The prediction are very sensitive to the physics
  details of cosmic ray propagation, particularly
  at low momentum. This is controlled by
  secondary/primary ratios, like B/C. AMS will
  measure the B/C ratio with high precision

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B/C measurement in AMS
Charge(Z) from TOF, Tracker and
RICH Rigidity(R) from Tracker and
Magnet Velocity(b) from TOF and RICH
? Mass and Charge
Charged nuclei
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Gamma detectors in space
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AMS response to positrons and protons
TRD signal
TOF signal
Tracker signal
RICH signal
ECAL signal
ECALTracker E/p matching
Positron
Proton
50
The AMS detector
TRD (Transition Radiation Detector) 20 layers of
Foam Straw Drift Tubes (Xe/CO2 ) 3D tracks, e/h
separationgt102 rej. up to 300 GeV
TOF (Time of Flight) 22 layers of
scintillators, Dt 160ps Trigger, Z separation,
b with few precision
Superconducting Magnet Nb-Ti coils in
superfluid He(1.8 ? K). Contained dipolar field
BL2 0.85 Tm2
1 m
Tracker 8 layers double sided silicon microstrip
detector sR(igidity)lt2 for Rlt10 GV, R up to 2-3
TV, Z separ.
RICH (Ring Imaging CHerenkov) 2 Radiators NaF
(center), Aerogel(elsewhere), b with 0.1
precision, Z and isotopes separation, (2
precision on mass below 10 GeV/n)
ECAL (Electromagnetic Calorimeter) Sampling
calorimeter LeadScint. Fibers trigger, e?, ?
detection sE(nergy) lt3 for Egt10 GeV, 3D
imaging e/h separationgt103 rej
2 m