An update on the High Energy End of the Cosmic Ray spectra M. Ave

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. Second knee 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 / m 2 /sec High energy 10 8 – eV Particles very rare 1/m 2 /year - 1/km 2 /century Extremely High Energy – eV Secondary particles make it to the ground Particles less plentiful 1/m 2 /sec - 1/m 2 /year Very High Energy – eV Secondary particles do not make it to the ground ACE 1m 2 TRACER 4m 2 Auger 3000km 2 How do we measure this radiation? Decrease in the information richness

The high energy tail of the Cosmic Ray spectrum (E> eV) Extragalactic origin Astrophysical candidates Exotic scenarios Topological defects, new interactions, massive particles decay, violation of Lorentz invariance…. γ=2.7

J. Cronin Pion photoproduction p + γ 2.7 K → N + π for E p > 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 eV10 20 eV Caveats (II): the spectral shape

Caveats (III) Do we expect anisotropies? First requirement eV 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 Sigl et al, Nucl. Phys. Proc. Suppl. 136: ,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 Mpc -3 Auger N+S 2030 Source density 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 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 nm light from de-excitation of atmospheric nitrogen (fluorescence light) ≈ 4 γ’s / m /electron eV 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 km 2 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

T tank + R tank / c ≈ T FD R tank T tank T FD

Energy calibration: model independent Statistical errors Systimatic errors

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 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 E event =f x E FD Θ X max S(1000) Observables f=1 FD scale f=1.3 SD scale f=1.3 S EM 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 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 catalague Angular scale: 3 degrees AGN distance cut: 75 Mpc Energy threshold: 57 EeV Significance after a prescription: 1.7 x Raw significance of the statistical test used: 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 anisotropic Correlation 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 ?