The Ultra-High Energy Cosmic Rays

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The Ultra-High Energy Cosmic Rays

• Introduction
• Data
• Acceleration and propagation
• Numerical Simulations
• (Results)
• Conclusions
• Isola Claudia
• Ecole Polytechnique / IAP- Paris

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Introduction

• 12 orders of magnitude on the energy and 30
  orders on the spectrum
• Two cut-off at the knee and at the ankle
  (galactic to extragalactic component)
• At around 109 eV solar origin
• Between 109 eV and 1015 eV Galactic origin (SNR)
• Between 1015 eV and 1018 eV probably Galactic
  origin but yet unclear
• Above 1019 eV unknown origin but very probably
  extra-galactic

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The showers
They reveal their existence only by indirect
effects Charged hadronic particles, electrons
and muons are recorded on the ground 1010-1011
particles on the ground 99 electrons (red) and
gamma (green) in the MeV energy range 1 muons
(blue) in the GeV energy range
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Detectiontwo techniques

• Direct observation of CR primaries is only
  possible from space
• Such detectors are limited in size - The highest
  energies require big surfaces

They are detected on the ground
Water Cherenkov or scintillation detectors AGASA
Fluorescence detector HiRes
The energy of the primary from the particle
density at 600m from the shower core the mass of
the primary from ?e/??
The energy of the primary from the quantity of
light produced the mass of primary from the
column depth Xmax
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Data

• Questions their origin, their nature and where
  does the spectrum ends?
• Three quantities arrival direction, mass of the
  primary particle, energy of the primary particle
• The angular distribution, the chemical
  composition, the spectrum

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The angular distribution

• Energy in the range (1-4) x1019 eV

• Energy in the range (4-10) x1019 eV
• Energy 1020 eV
• Doublets
• Triplet

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The chemical composition

• Flys eye data
• Theoretical prediction for the iron
• Theoretical prediction for protons
• Simple two component model
• Transition from heavy to light component
• Transition from galactic to extragalactic origin

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The spectrum
AGASA and HIres are not consistent at the highest
energies Does a GZK cut-off exist?
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The Pierre Auger Project

• A combination of a ground array and one or more
  fluorescence detectors
• Effective aperture about 200 times as large as
  the AGASA array
• 1700 particle detectors covering about 3000 Km2
• 50-100 events per year above 1020 eV
• It is planned to construct one site in each
  hemisphere (Argentina and Utah)

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How can they achieve these energies?
Top-Down
Bottom-Up

• Decay from a supermassive paticle X
• Topological defects or metastable particles from
  inflation
• Final products ?,?,?

• Statistical acceleration in a magnetized plasma
• Fermi mechanism
• Power law spectrum
• Supernovae, Hot spot of radio galaxies, Actif
  galactic nuclei

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The GZK cut-offPhysics beyond the Standard Model?

• The nucleons interact with the background photons
• Threshold energy for a photo-pion reaction
• Energy loss
• Mean free path

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The cross section for the photo-pion reaction
Attenuation lenght
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Few objets as possible sources
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• In general we cannot achieve the maximal value
  Emax because of the energy losses at the source
  from synchrotron radiation and photo-pion reaction

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The angular distribution Two possibilities

• Many Sources
• A few sources but a strong magnetic field
• This could explain the absence of correlation
  between the arrival direction and powerful
  astrophysical objects
• The isotropy at large scale as a diffusion
  effect
• The clusters at small scales as a magnetic
  lensing effects

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The numerical simulation

• The purpose is to test theoretical models by
  using a numerical code
• The code simulates the propagation of charged
  particle in an extragalactic magnetic field by
  taking into account the energy losses
• The results are strongly affected by the magnetic
  field

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The effect of magnetic fields

• Deflection
• Time delay
• Diffusion
• They affect the angular distribution, the
  clusters, the spectrum and the chemical
  composition

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The code

• We assume a random turbulent magnetic field
• We use nB-11/3 -gtKolmogorov turbulence
• L characterize the coherence length of the
  magnetic field
• 5000 trajectories are computed for each magnetic
  field realization
• 20 realizations in total
• Each trajectory is followed for a maximal time of
  10 Gyr

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Centaurus A (I)One single source at 3.4 Mpc
B0.3?G
B0.3?G
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Centaurus A (II)
B0.3?G
B1?G
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The Local SuperCluster

• Distribution of sources
• We take a discrete distribution of sources
  centered at 20 Mpc from Earth and distributed on
  a sheet of thickness 3 Mpc and radius 20 Mpc,
  with the source density following the profile of
  the shee
• The auto-correlation function

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Auto-correlation function (I)
100 sources and B0.05 µG
100 sources and B0.3 µG
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Auto-correlation function (II)
5 sources and B0.3 µG
10 sources and B0.3 µG
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The spectrum
10 sources and B0.3 µG E-2 injection spectrum
Sources in a sphere of 40 Mpc around the Local
Supergalactic center
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Centaurus A (again)
Agasa exposure function
Auger exposure function
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Heavy nuclei
The maximal acceleration energy depends linearly
on the charge Ze
The deflection is also proportional to the charge
Ze
Heavy nuclei are attenuated basically by two
processes photodisintegration on the diffuse
photon backgrounds and creation of e pairs
n(?) is the photon density of the ambient
radiation We include the contributions from three
different components infra-red, CMB and
Universal Radio Background
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The energy loss time
Helium
Silicon Carbon
Iron
At energies above 1020 eV the heaviest nuclei
start to disintegrate more quickly The
multi-nucleon emission becomes more important
compared to one or two nucleon emission
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Chemical composition
B10-12G
B2x10-8G
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The observed spectra
All particle spectrum observed at distances
d1.5, 2.3,3.2,4.8,7.1,10.5,15.5,33.9,50 Mpc
(dotted line)
B2x10-8G
B10-12G
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Applications
Anchordoqui et al. Iron nuclei accelerated in two
nearby starbust galaxies. Hard injection
spectrum.
Ahn et al. UHECR originate from M87, deflected in
a powerful galactic magnetic field. The two
highest energy events He nuclei.
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Conclusions

• Many questions are still open on the Ultra High
  Energy Cosmic Rays
• Their origin (source and acceleration mechanism),
  their nature and the end of the spectrum
• We used a numerical code to simulate some
  possible scenarios and we were able to ruled out
  some of the scenarios proposed
• We plan to implement our code and combine it with
  the new statistics coming from Auger
• The very next future years will be crucial to
  solve this mistery