1. Signatures of Protons in UHECR Transition from Galactic to
Extragalactic Cosmic Rays
Roberto Aloisio
INFN – Laboratori Nazionali del Gran Sasso
Aspen Workshop on Cosmic Rays Physics
Aspen April 2007

2. Chemical Composition Similar limits from AGASA
No conclusive observations at energies E>1018 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 eV)
to light composition (at ~1019 eV)
Haverah Park [Ave et al. 2001]
No more than 54% can be Iron above 1019 eV
No more than 50% can be photons above eV
Similar limits from AGASA
CONTROLLARE I RISULTATI DI AUGER SULL’ELONGATION RATE………………. CITARE IL TALK DI ABU-ZAYYAD SUGLI ULTIMI RISULTATI DI HIRES CHE INDICANO UNA COMPOSIZIONE LEGGERA GIA PER E>10^{18} eV.
Proton composition at E>1018 eV
not disfavored by experimental
observations
HiRes elongation rate

3. The End of the CR Spectrum?
The last HiReS analysis confirms the expected Greisen Zatzepin Kuzmin suppression in the flux with E1/2= 0.07 eV in perfect agreement with the theoretically predicted value for protons E1/2= (Berezinsky & Grigorieva 1988)
HiRes collaboration (2007)
Add Auger spectrum
Strong evidences of an astrophysical proton
dominated flux at the highest energies

4. UHE Proton energy losses
protons
CMB
Universe size
1000 Mpc
Adiabatic losses
Universe expansion
log10[ latt (Mpc)]
100 Mpc
Pair production
p   p e+ e-
Photopion production
p   p 0
 n 
log10[ E (eV)]

5. UHE Nuclei energy losses
Pair production
A   A e+ e-
UHE Nuclei energy losses
Universe size
Iron
helium
Universe size
Pair production energy losses
produce an early onset in the
photo-disintegration flux depletion
Photodisintegration
A   (A-1) N
 (A-2) 2N
Depletion of the flux
Iron E  1020 eV
Helium E 1019 eV

6. Protons propagation in Intergalactic Space
Berezinsky, Grigorieva, Gazizov (2006)
Continuum Energy Losses
Protons lose energy but do not disappear.
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 ns.
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
γ > injection power law
Jp=Lp nS source emissivity
model parameters

7. Modification Factor DIP (p + CMB  p + e+ + e- )
Jpunm(E) only redshift energy losses
Jp(E) total energy losses
DIP (p + CMB  p + e+ + e- )
GZK cut-off (p + CMB  N + )
Tiny dependence on the
injection spectrum

8. Proton Dip Best fit values: γ = 2.7 Jp = O(10 erg s-1Mpc-3
Insert a slide in between with the definition of the modification factor….
Berezinsky et al. ( )

9. 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
minimum χ2)
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)
λAGASA = 0.90

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

11. the injection spectrum has < 2.4
Caveats
The interpretation of the observed
Spectrum in terms of protons
pair-production losses FAILS if:
the injection spectrum has < 2.4
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)
RA, Berezinsky, Grigorieva (2007)

12. Diffusive shock acceleration tipically shows
Maximum energy distribution
Diffusive shock acceleration tipically shows
 2.1  2.3
The maximum acceleration energy is fixed by the geometry of the source and its magnetic field
If the sources are distributed over Emax: (β ≈ 1.5)
the overall UHECR generation rate has a steepening at some energy Ec (minimal Emax O(1018 eV))
E < Ec
E > Ec
Kachelriess and Semikoz (2005)
RA, Berezinsky, Blasi, Grigorieva, Gazizov (2006)

13. Steepening in the flux at The DIP survives also with IMF
The IMF effect on the UHE proton spectrum
Steepening in the flux at
E1018 eV 2nd Knee
no IMF
The DIP survives also with IMF
=2.7
B0=1 nG, lc=1 Mpc
The beginning of 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 cut-off is due to a suppression in the maximal contributing distance its position depends on the IMF.
The low energy behavior (E<1018 eV) depends on the diffusive regime.
RA & Berezinsky (2005)
Lemoine (2005)
Combination of the UHECR low energy
tail with the HE tail of galactic CR
(transition Galactic-ExtraGalactic see later)
Magnetic Horizon – Low Energy Steepening
The diffusive flux presents a steeping due to proton energy losses and at lower energies an exponential suppression due to the magnetic horizon.

14. Galactic and ExtraGalactic I
dip scenario
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): E2K  1018 eV.
with IMF
without IMF
 =2.7
=2.7
RA & Berezinsky (2005)

15. Allard, Parizot, Olinto (2005-2007)
Galactic and ExtraGalactic II
The transition is placed at Etr  31018 eV
The composition is dominated by galactic nuclei at E<Etr ,
by extra-galactic nuclei at E>Etr and by extra-galactic protons
at the highest energies
mix comp scenario
Allard, Parizot, Olinto ( )
High (Emax>1018 eV) maximum energy of galactic CR
Difficult to detect (nuclei before and after the transition)

16. Galactic and ExtraGalactic III
ankle scenario
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  2.1 
Problems in the Galactic component
Galactic acceleration: Maximum acceleration energy required is very high Emax 1019 eV
Composition: How the gap between Iron knee EFe 1017eV and the ankle (1019 eV) is filled

17. Conclusions 1. Observation of the dip
Spectrum in the range eV could represent a
signature of the proton interaction with CMB (as the GZK
feature).
2. Where is the transition Galactic-ExtraGalactic CRs?
Precise determination of the mass composition in the energy
range eV.
ExtraGalactic CR (protons) at E ≥ eV (dip scenario)
discovery of proton interaction with CMB
confirmation of conservative models for Galactic CR
challenge for the acceleration of UHECR (steep injection γ > 2.4)
Galactic CR (nuclei) at E ≥ eV (ankle and mixed composition scenario)
challenge for the acceleration of CR in the Galaxy (high Emax)