P1259073928vgjzA

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Propagation and Composition of Ultra High Energy
Cosmic Rays
Roberto Aloisio
INFN Laboratori Nazionali del Gran Sasso
6th Rencotres du Vientnam
Challenges in Particle Astrophysics
Hanoi 6-12 August 2006
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GZK
2nd Knee
Ankle
Knee
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The first fuzzy picture of the UHECR sky
At most one source in the angular bin of 3
degrees! The sources should have been seen in
particular at 1020 eV Correlation??? if no
correlations found Bursting Sources??? or High
Magnetic Fields??? or Exotic Models???
Using many realizations (MC)
ns ? 10-5 Mpc-3
40 sources within 100 Mpc (20 degrees between
sources)
Blasi De Marco (2003) Kachelriess Semikoz
(2004)
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Chemical Composition
No conclusive observations at energies Egt1018 eV
Hires, HiresMIA, Yakutsk proton
compositionFlys Eye, Haverah Park, Akeno
mixed composition
Hires elongation rate
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UHE Proton energy losses
protons
CMB
Universe size
1000 Mpc
log10 latt (Mpc)
100 Mpc
Photopion production p ? ? p ?0
? n ??
log10 E (eV)
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UHE Nuclei energy losses
helium
Universe size
Pair production has no particular effect on the
flux

• Depletion of the flux
• Iron E ? 1020 eV
• Helium E? 1019 eV

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Injection spectrum number of particles
injected at the source per unit time and energy
Modification factor
Jpunm(E) only redshift energy losses Jp(E)
total energy losses
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The energy losses suffered by protons leave their
imprint on the spectrum
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Akeno AGASA
Berezinsky et al. (2002-2005)
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Robustness and Caveats

• Protons in the Dip come from large distances,
• up to 103 Mpc. The Dip does not depend on
• inhomogeneity, discreteness of sources
• maximum energy at the source
• intergalactic magnetic fields (see later...)

The interpretation of the DIP in terms of
protons pair-production FAILS if
RA, Berezinsky, Grigorieva (2006)
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The maximum acceleration energy is fixed by the
geometry of the source and its magnetic field
the overall UHECR generation rate has a
steepening at some energy Ec (minimal Emax
O(1018 eV))
Kachelriess and Semikoz (2005) RA, Berezinsky,
Blasi, Grigorieva, Gazizov. (2006)
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Different experiments show different systematic
in energy determination
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Intergalactic Magnetic Fields
Very poor experimental evidences
Effect of IMF on UHECR
deflection
isotropization
diffusion
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Numerical simulations
Numerical determination of the IMF is based on
LSS and MHD simulations
Puzzling results by different groups
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• Rigidity models can be rigidity-confinement
  models or rigidity-acceleration models.
• The energy of spectrum bending (knee) for nucleus
  Z is Ez Z Ep, where Ep 31015 eV is the
  proton knee. For Iron EFe 81016 eV.

proton
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?
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Kascade data
BUT
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• The Galactic CR spectrum ends in the energy range
  1017 eV, 1018 eV.
• 2nd Knee appears naturally in the extragalactic
  proton spectrum as the steepening energy
  corresponding to the transition from adiabatic
  energy losses to pair production energy losses.
  This energy is universal for all propagation
  modes (rectilinear or diffusive) E2K1018 eV.

RA Berezinsky (2005)
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• Traditionally (since 70s) the transition
  Galactic-ExtraGalactic CR was placed at the ankle
  ( 1019 eV).
• In this context ExtraGalactic protons start to
  dominate the spectrum only at the ankle energy
  with a more conservative injection spectrum gg
  2.0 ? 2.2.

Problems for the Galactic component

• Galactic acceleration Maximum
  acceleration energy required is very high Emax
  1019 eV
• Composition How
  the gap between Iron knee EFe1017eV and the
  ankle (1019 eV) is filled

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1. Is there the GZK feature? Auger will
soon clarify this point. First results seem to
favor the GZK picture.
2. Is there a dip? Spectrum in the range
1018 - 1019 eV could be a signature of
proton interaction with CMB (as the GZK feature).
3. Where is the transition Galactic-ExtraGalactic
CRs? Precise determination of the mass
composition in the energy range 1018 -
1019 eV.