This paper is intended to be pedagogic. The first part is devoted to a brief exposition of the physics associated with the development of extensive air showers. This is seen as being relevant to any student beginning studies in this field. The latter part of the paper deals with methods of detection of extensive air showers, in a general way, and with results on the energy spectrum, arrival direction and mass distribution of cosmic rays of energy above 10 18 eV. Finally, proposals for explaining the anomalous existence of the very highest energy cosmic rays are briefly discussed and forthcoming methods of detection through the Pierre Auger Observatory and the Extreme Universe Space Observatory (EUSO) are described shortly.

Extensive Air Showers and Ultra High Energy Cosmic Rays

The discovery of extensive air showers by Rossi, Schmeiser, Bothe, Kohlhorster and Auger at the end of the 1930s, facilitated by the coincidence technique of Bothe and Rossi, led to fundamental contributions in the field of cosmic ray physics and laid the foundation for high-energy particle physics. Soon after World War II a cosmic ray group at MIT in the USA pioneered detailed investigations of air shower phenomena and their experimental skill laid the foundation for many of the methods and much of the instrumentation used today. Soon interests focussed on the highest energies requiring much larger detectors to be operated. The first detection of air fluorescence light by Japanese and US groups in the early 1970s marked an important experimental breakthrough towards this end as it allowed huge volumes of atmosphere to be monitored by optical telescopes. Radio observations of air showers, pioneered in the 1960s, are presently experiencing a renaissance and may revolutionise the field again. In the last 7 decades the research has seen many ups but also a few downs. However, the example of the Cygnus X-3 story demonstrated that even non-confirmable observations can have a huge impact by boosting new instrumentation to make discoveries and shape an entire scientific community.

https://link.springer.com/content/pdf/10.1140%2Fepjh%2Fe2012-30013-x.pdf

Extensive Air Showers and Ultra High-Energy Cosmic Rays: A Historical Review

The status of the field of ultrahigh energy cosmic-ray physics is summarized, from the point of view of the latest results of the High-Resolution Fly's Eye (HiRes) Experiment. HiRes results are presented, and compared with those of the Akeno Giant Air Shower Array (AGASA), plus the Telescope Array and Pierre Auger experiments. The HiRes measurement of the cosmic-ray spectrum and the observation of the GZK cutoff are presented. HiRes results on composition, searches for anisotropy, measurement of the proton-air total cross-section and shapes of shower profiles are presented.

/pdf/highest-energy-cosmic-rays-and-results-from-the-hires-3ee52svicb.pdf

Highest energy cosmic-rays and results from the HiRes experiment

/pdf/from-ultra-rays-to-astroparticles-5u1etuzad8.pdf

From Ultra Rays to Astroparticles

The experiments on the search for the end of the cosmic-ray energy spectrum with the particle detector array technique and the optical (Cerenkov and/or fluorescence) technique are summarized. In the highest observed energy region, the suppression of the flux above about 6×1019 eV, which corresponds to the so-called 'Greisen–Zatsepin–Kuz'min (GZK) cutoff energy', is confirmed by the new results from the High-Resolution Fly's Eye (HiRes) and the Pierre Auger Observatory (Auger). Summarizing the spectra observed from 1014 to 1020 eV with world wide experiments, there is still room for further investigations on the energy scale and the flux of primary cosmic rays. In order to establish the energy scale, it is necessary not only to understand the optical technique further, but also to determine the primary species in the highest energy region. Also, it is important to make more detailed measurements on the energy spectrum in the 1017–1018 eV region. To observe the super-GZK events and the anticipated recovery of the spectrum above the GZK cutoff, the search for the end of cosmic-ray energy spectrum will be continued even after a century since the discovery of cosmic rays in 1912.

https://iopscience.iop.org/article/10.1088/1367-2630/11/6/065012/pdf

Search for the end of the energy spectrum of primary cosmic rays

The Cornell University Cosmic Ray Group is pursuing an experimental attack on the problem of detecting and analyzing ultra-high-energy air showers by the optical emission m the atmosphere. A technique has been developed to record pulses of light from a sequence of adjacent positions in the night sky, by imaging a sector of the sky onto a mosaic of photomultiplier tubes nested in the focal surface of a large Fresnel lens. Sixteen such lens units are then necessary to view a full 2π steradians. It is shown that, in the wavelength region 3 400 to 4 500 A, Cerenkov radiation dominates the first 23° from the point of appearance of the shower, while nitrogen fluorescence allows tracking of the shower beyond 23°.

P. B. Landecker

Papers

An imaging system for EAS optical emission