An update on the High Energy End of the Cosmic Ray spectra

M. Ave

E−2.7

Charged particles with a Non Thermal Spectrum

Goal: the mechanism that produce these particles.

Different quest than looking for experimental signatures that confirms/rejects a given theory, but with the same goal.

E− 3

E−3. 3

Second knee

E− 3

Sources are hidden by the magnetic fields

Spectral Features: knee, ankle, second knee?

Chemical composition and its dependence with energy

Anisotropies at different energies.

• X-Ray, Gamma Ray observations

• Neutrino Astronomy

Direct

Indirect

Photon background spectrum

Lots of Particles 1000 / m2 /sec

High energy 108 – 1010 eV

Particles very rare 1/m2/year - 1/km2/century

Extremely High Energy1016 – 1021 eV

Secondary particles make it to the ground

Particles less plentiful 1/m2/sec - 1/m2/year

Very High Energy1010 – 1015 eV

Secondary particles do not make it to the ground

ACE 1m2

TRACER 4m2

Auger 3000km2

How do we measure this radiation?

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The high energy tail of the Cosmic Ray spectrum (E> 1019 eV)

Extragalactic origin

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Topological defects, new interactions, massive particles decay, violation of Lorentz invariance….

γ=2.7

J. Cronin

Pion photoproduction

p + γ2.7 K → N + π

for Ep > 5 10 19 eV

Interaction length ≈ 6 Mpc

Energy loss ≈ 20 %/interaction

nearby sources (<50 Mpc)

Caveats (I): the particle horizon/ GZK effect

There is no containment volume (the galaxy), so the observed spectra should be the source spectra.

But, the spectral index is far from the Non-Linear Shock Acceleration predictions.

Cosmological evolution and GZK cutoff change the slope of the spectra

The higher the energy the closer the source.

1019 eV 1020 eV

Caveats (II): the spectral shape

ϒ≈4

M 21

Caveats (III) Do we expect anisotropies? First requirement.

1019 eV

1020 eV

Simulations of Large scale Structure Formation to study the build up of magnetic fields through magnetohydrodynamical amplification from a seed at high redshift.

Dolag et al, JCAP 0501:009,2005

Cosmic Rays will propagate mostly through voids, so we should be in the balistic regime.

However, other calculations seem to be in disagreement: deflections can be as large as 100.

Sigl et al, Nucl. Phys. Proc. Suppl. 136: 224-233,2004

The departure from isotropy depends on:The density of CR sources.The distribution of sources in the sky.The statistics of the experiment.

Sources distributed anisotropically?

AGN (z < 0.02)

IRAS galaxies (z < 0.02)

Sources distributed isotropically?

Auger N+S 2014

Source density 10-5 Mpc-3

Auger N+S 2030

Source density 10-3 Mpc-3 Note: we need a redshift cutoff, if

not the universe is very isotropic

Caveats (III) Do we expect anisotropies? Second requirement.

We expect anisotropy at some level

Particle horizons decrease with energy, above 1019.7 eV below 100 Mpc:

The number of observable sources decreases. The distribution of matter below 100 Mpc is anisotropic (filaments, clusters..., the cosmic web).

If the sources resemble/follow the distribution of matter, anisotropy is expected at some level, even if we have less than one event per source.

Somewhere in this energy range a transition from Galactic to Extagalactic origin is predicted. But where?

Caveats (IV): What do we know about the chemical composition?

The Detector: Pierre Auger Observatory

Fluorescence Detector

• E + longitudinal development

• Time ≈ direction

• ≈ 10% duty cycle

300-400 nm light from de-excitation of atmospheric nitrogen

(fluorescence light) ≈ 4 γ’s / m /electron

1019 eV 1010 e

Surface Detector

• Shower size ≈ E

• Time ≈ direction

• 100% duty cycle

Cross-calibration, improved resolution, control of systematic errors

14

The Observatory

Surface Array 1600 detector stations 1.5 km spacing 3000 km2

Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per

enclosure 24 Telescopes total

Tank with antenna pointing to one of the communication towers.

Three tanks aligned in the middle of the Pampa

Ttank + Rtank / c ≈ TFD R ta

nk

Ttank

TFD

Energy calibration: model independent

Sta

tistic

al e

rror

sS

ystim

atic

err

ors

Checking the Energy Scale: SD+Shower universality

Model independent parameterization of Ground signals

Constant Number of events for equal exposure bins

Only possible if we know the average X

max as a function of energy!!

DG

S(1000,Θ=38)= 38.9 ± 1.4 (stat) ±2.0 (sys)

At a reference energy of 1019 eV

SD+Shower Universality

Hybrid

S(1000,Θ=38)= 50.0 ± 3 (stat) ±11 (sys)

They do differ by 30%

Cross checks with Hybrid Events

Eevent

=f x EFD

Θ X

max

S(1000)

Observables

f=1 FD scalef=1.3 SD scale

f=1.3

SEM

can be predicted from

the observables and substracted out to the measured S(1000) .

Collateral benefit: learn about hadronic models at these energies?

A preliminary study indicates 40% more muons than model prediction. But it could be a factor of two.

Knee

LHCf and Totem will help in this issue

Finally the UHECR spectrum There is a clear flux suppression above 1019.6 eV

Chemical Composition: uncertainty in Hadronic model predictions

Transition

Inherent degeneracy between hadronic models and Chemical composition. The data in the fluctuations (not model dependent) combined with N

μ measurents will help.

What about our arrival directions?

28 highest energy events

Equatorial coordinates

Moreover there is a correlation with nearby matter distribution...

Correlations with AGNs in VC catalagueAngular scale: 3 degreesAGN distance cut: 75 MpcEnergy threshold: 57 EeVSignificance after a prescription: 1.7 x 10-3

Raw significance of the statistical test used: 10-5

Millenium Simulation

But, what does it mean this result in the flow chart of identifying the mechanisms that produces the highest energy particles in nature?:

The UHECR sky is anisotropicCorrelation with the distribution of nearby matter.Identification of the sources.Identification of the mechanism that accelerate these particles.

The mentioned results mixed these 3 items.

We almost double the data since the last report to the community. These statistics will help to know where we are.

Conclusions

Charge particle astronomy?

Cosmic Ray Experiments as a particle physics Lab?