I. C. Maris

Active Galactic Nuclei: Sources for ultra high energy cosmic rays?

The origin of ultra high energy cosmic rays promises to lead us to a deeper understanding of the structure of matter. This is possible through the study of particle collisions at center-of-mass energies in interactions far larger than anything possible with the Large Hadron Collider, albeit at the substantial cost of no control over the sources and interaction sites. For the extreme energies we have to identify and understand the sources first, before trying to use them as physics laboratories. Here we describe the current stage of this exploration. The most promising contenders as sources are radio galaxies and gamma ray bursts. The sky distribution of observed events yields a hint favoring radio galaxies. Key in this quest are the intergalactic and galactic magnetic fields, whose strength and structure are not yet fully understood. Current data and statistics do not yet allow a final judgement. We outline how we may progress in the near future.

Layered water Cherenkov detector for the study of ultra high energy cosmic rays

We present a new design for the water Cherenkov detectors that are in use in various cosmic ray observatories. This novel design can provide a signicant improvement in the independent measurement of the muonic and electromagnetic component of extensive air showers. From such multi-component data an event by event classication of the primary cosmic ray mass becomes possible. According to popular hadronic interaction models, such as EPOS-LHC or QGSJetII-04, the discriminating power between iron and hydrogen primaries reaches Fisher values of 2 or above for energies in excess of 10 19 eV with a detector array layout similar to that of the Pierre Auger Observatory.

A likelihood method to cross-calibrate air-shower detectors

Abstract We present a detailed statistical treatment of the energy calibration of hybrid air-shower detectors, which combine a surface detector array and a fluorescence detector, to obtain an unbiased estimate of the calibration curve. The special features of calibration data from air showers prevent unbiased results, if a standard least-squares fit is applied to the problem. We develop a general maximum-likelihood approach, based on the detailed statistical model, to solve the problem. Our approach was developed for the Pierre Auger Observatory, but the applied principles are general and can be transferred to other air-shower experiments, even to the cross-calibration of other observables. Since our general likelihood function is expensive to compute, we derive two approximations with significantly smaller computational cost. In the recent years both have been used to calibrate data of the Pierre Auger Observatory. We demonstrate that these approximations introduce negligible bias when they are applied to simulated toy experiments, which mimic realistic experimental conditions.

Measurement of the energy spectrum of cosmic rays at the highest energies using data from Pierre Auger Observatory

We report a measurement of the flux of cosmic rays with unprecedented precision and statistics using data from the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one station of the surface detector we derive a spectrum for energies above 1 EeV. We also report on the energy spectra obtained with the surface detector array. The spectral features are presented in detail and the impact of systematic uncertainties on these features are addressed.