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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
The spectrum of CR's

                              2nd Knee   Ankle
 The first fuzzy picture of the UHECR sky

                                                              Small angle clustering gives
                                                              indications about the source
                                                                    number density

                                                                At most one source in the
                                                                angular bin of 3 degrees!
                                                                The sources should have
                                                                 been seen in particular
                                CAVEAT                                 at 1020 eV

                                Recently Blasi, De Marco and Olinto foundCorrelation???
                                a 5σ inconsistency between the spectrum and
                                                                    if no
                                the small scale anisotropies measured by correlations found
                               Using many realizations (MC)
As nS decreases (fixed flux)    AGASA.
 sources become brighter            ns  10-5 Mpc-3                   Bursting Sources???
    with an increase in           40 sources within 100 Mpc                    or
  clustering probability       (~20 degrees between sources) High Magnetic Fields???
                                       Blasi & De Marco (2003)
                                     Kachelriess & Semikoz (2004)       Exotic Models???
Chemical Composition
      No conclusive observations at energies E>10 18 eV
                                          Hires, HiresMIA, Yakutsk
                                             proton composition
                                       Fly’s Eye, Haverah Park, Akeno
                                              mixed composition

                                   Fly's Eye [Dawson et al. 98]
                                   Transition from heavy (at 10 17.5 eV)
                                   to light composition (at ~10 19 eV)

                                   Haverah Park [Ave et al. 2001]
                                   No more than 54% can be Iron above 10 19 eV
                                   No more than 50% can be photons above 4 10 19 eV

                                    Similar limits from AGASA

                                   Proton composition at E>1018 eV
           Hires elongation rate    not disfavored by experimental
UHE Proton energy losses

                     Universe size
log10[ latt (Mpc)]

                           1000 Mpc
                                                           Adiabatic losses
                                                          Universe expansion
                                     100 Mpc

                                                                Pair production
                                                               p   p e+ e-

                                                            Photopion production
                                                              p   p 0
                                                                   n 
                                         log10[ E (eV)]
                                                    Pair production
UHE Nuclei energy losses                       A   A e+ e-

     Universe size
                                    Universe size

     Pair production has no
    particular effect on the flux
    Depletion of the flux
                                                A   (A-1) N
       Iron   E  1020 eV
                                                     (A-2) 2N
       Helium E 1019 eV
Protons propagation in Intergalactic Space
 Continuum Energy Losses
  Protons lose energy but do not disappear.

                                                                                             Blasi, De Marco, Olinto (2003)
  Fluctuations in the pγ interaction start to
  be important only at E>5  1019 eV.
   Uniform distribution of sources
   the UHECR sources are continuously
   distributed with a density n s.

   Discrete sources
   the UHECR sources are discretely
   distributed with a spacing d.                Injection spectrum number of particles injected
                                                at the source per unit time and energy

     Modification factor
                                                          model parameters
                                                          γg > 2 injection power law
    Jpunm(E) only redshift energy losses                  Lp source luminosity
    Jp(E) total energy losses                             ns (d) source density (spacing)
UHECR proton spectrum
The energy losses suffered by protons leave their imprint on the spectrum
 DIP     p+          p + e+ + e–          GZK p+               N+

                               sources distribution (mainly GZK)
  These features depend on     injection spectrum (mainly DIP)
                               way of propagation (magnetic fileds)
Proton Dip
                              Experimental evidence of the Dip

      Akeno AGASA

                     Best fit values:
                     γg = 2.7
                     <Lp> = 4  1043 erg/s
                     ns = 3  10-5 Mpc-3

                    Berezinsky et al. (2002-2005)
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

                                                      RA, Berezinsky, Grigorieva (2006)
  intergalactic magnetic fields (see later...)

The interpretation of the DIP in terms
of protons pair-production FAILS if:

   heavy nuclei fraction at E>1018 eV
   larger than 15% (primordial He
       has nHe/nH0.08)
                           Berezinsky et al. (2004)
                           Allard et al. (2005)
                           RA et al. (2006)

   the injection spectrum has g< 2.4
              Diffusive shock acceleration tipically shows

Maximum energy distribution
  The maximum acceleration energy is
  fixed by the geometry of the source and
  its magnetic field

  If the sources are distributed over E max:                           (β ≈ 1.5)

  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)
Energy calibration by the Dip
 Different experiments show different systematic in energy determination

Calibrating the energy through the Dip gives an energy shift E→ λE (fixed by χ2)
         λAGASA = 0.90        λHiRes = 1.21       λAuger = 1.26

    NOTE: λ<1 for on-ground detectors and λ>1 for fluorescence light detectors
          (Auger energy calibration by the FD)
Intergalactic Magnetic Fields

                   Very poor experimental evidences

                                       Large Scale Structures are characterized
                                       by magnetic field produced from compression
  Cosmological origin                  and twisting of the primordial field
      Faraday rotation                 Voids are characterized by an appreciable
                                       magnetic field

                                       Magnetic field concentrated around sources,
                                       i.e. in Large Scale Structures
  Astrophysical sources
 Synchrotron and ICS emission          No appreciable field in most part of the
                                       universe volume

  Effect of IMF on UHECR

              deflection        diffusion         isotropization
Numerical simulations
   Numerical determination of the IMF is based on LSS and MHD simulations
                          Puzzling results by different groups
   Dolag, Grasso, Springel & Tkachev                         Sigl, Miniati & Ensslin use an
  use constrained simulations, being able                      unconstrained simulation
      to reproduce the local Universe                           putting the observer *
                                                                    close to a cluster
   Low B (0.1 nG in filaments and 0.01 nG in voids)   High B (100 nG in filaments and 1 nG in voids)
   Low deflection angles: < 1° at 4 1019 eV           High deflection angles: up to 20° at 1020 eV
   UHECR astronomy is allowed                         UHECR astronomy nearly impossible
The IMF effect on the UHE proton spectrum
                     Magnetic Horizon – Low Energy Steepening
      The diffusive flux presents an exponential suppression at low energy and a
                             steepening at larger energies.

  The low energy cut-off is due
  to a suppression in the
  maximal contributing
  distance (magnetic horizon),                                no IMF       g=2.7
  its position depends on the           The DIP survives also with IMF

  The steepening is independent
  of the IMF, it depends only on
  the proton energy losses and
  coincides with the observed
  2nd Knee.

  The low energy behavior
  (E<1018 eV) depends on the           Steepening in the flux at
  diffusive regime.Berezinsky (2005)
               RA &                     E1018 eV 2nd Knee
                Lemoine (2005)
Galactic Cosmic Rays
  Rigidity models can be rigidity-confinement models or rigidity-acceleration

  The energy of spectrum bending (knee) for nucleus Z is Ez = Z Ep, where
  Ep  3×1015 eV is the proton knee. For Iron EFe 8´1016 eV.




Kascade data                     Kascade data 2003:
                              seem to confirm the rigidity

                            Kascade data 2005:
               different results with different Monte Carlo
                   approaches in data reconstruction.
                     Rigidity scenario not confirmed.
Galactic and ExtraGalactic I
  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

                                                                                 RA & Berezinsky (2005)
  propagation modes (rectilinear or diffusive): E2K1018 eV.

                           g=2.7                                       g=2.7

     with IMF                                   without IMF
Galactic and ExtraGalactic II
   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 g  2.0 

Problems for the Galactic component

  Galactic acceleration:
  Maximum acceleration energy
  required is very high E max 1019 eV

  How the gap between Iron knee
  EFe1017eV and the ankle (10 19 eV)
  is filled
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.

 Galactic CR (nuclei) at E ≥ 1018 eV
    challenge for the acceleration of CR in the Galaxy (Emax  EFe)

 ExtraGalactic CR (protons) at E ≥ 1018 eV
     discovery of proton interaction with CMB
     confirmation of conservative models for Galactic CR
     models for the acceleration of UHECR with γg > 2.4