Astroparticle Physics

6.1 Charged Component of Primary Cosmic Rays 83small (< 10 −4 ). Furthermore, the observed zenith-angledistribution of energetic events and the position of primaryvertices of the cascade development in the atmosphere areinconsistent with the assumption that primary neutrinos areresponsible for these events. Because of their low interactionprobability one would expect that the primary vertices forneutrinos would be distributed uniformly in the atmosphere.In contrast, one observes that the first interaction takes placepredominantly in the 100 mbar layer which is characteristicof hadron or photon interactions. One way out would be toassume that after all protons are responsible for the eventswith energies exceeding 6 × 10 19 eV. This would supportthe idea that the sources of the highest-energy cosmic-rayevents are relatively close. A candidate source is M87, anelliptic giant galaxy in the Virgo cluster at a distance ofneutrino origin15 Mpc. From the center of M87 a jet of 1500 pc length is M87, a sourceejected that could be the source of energetic particles. M87 of cosmic rays?coincides with Virgo A (3C274), one of the strongest radiosources in the constellation Virgin.A close look at the experimental situation (see Fig.6.5) shows that the two major experiments measuring inthe ≤ EeV range do not agree in absolute intensity andalso not in the shape of the spectrum for energies in excessof ≈ 5 × 10 19 eV. Even though the HiRes experimentfinds events beyond 10 20 eV, the HiRes spectrum is not indisagreement with the expectation based on the GZK cutoff,quite in contrast to the AGASA findings. One mightargue that possibly the energy assignment for the showersfrom HiRes is superior over that from AGASA sinceHiRes records the complete longitudinal development of theshower, while AGASA only samples the shower informationin one atmospheric layer, i.e., at ground level.It is to be expected that the Auger experiment will clarifythe question concerning the GZK cutoff. In this context it isinteresting to note that the Auger-south array has recordedan event with ≈ 10 20 eV already during the constructionphase [4]. The full Auger-south detector will be completedin spring 2006.Considering the enormous rigidity of these high-energyparticles and the weakness of the intergalactic magnetic fieldone would not expect substantial deflections of these particlesover distances of 50 Mpc. This would imply that one canconsider to do astronomy with these extremely high-energycosmic rays. Since there is no correlation of the arrival di-rections of these high-energy cosmic-ray events with knownHiRes vs. AGASAAuger experimentexotic particles?