**A. Extragalactic Cosmic Rays:**


## **B. Galactic Cosmic Rays:**


This book contains works on both theoretical principles as well as results from experimental researches crucial for understanding the origin of cosmic rays.

The editors believe that this book will be interesting to both theorists and scientists working in modern experiments.

Interdisciplinarity is a strong theme of this book. We believe that cosmic rays are not sepa‐ rated from other scientific fields but form one of the crucial bases of modern astrophysics especially because the theoretical researches on the origin of cosmic rays are leading to a number of puzzling observations that indicate a much more complex astrophysical scenario, which we are far from understanding.

**Zbigniew Szadkowski**

Faculty of Physics and Applied Informatics Department of High-Energy Astrophysics University of Łódź, Poland

**Section 1**

**Extragalactic Cosmic Rays**

**Extragalactic Cosmic Rays**

**Chapter 1**

**Provisional chapter**

**Introductory Chapter: Ultrahigh-Energy Cosmic Rays**

In 1938, Pierre Auger recorded coincidences by particle detectors separated by large distances at ground level. The source was ultrahigh energy cosmic rays (UHECRs) generating in the atmosphere extensive air showers (EAS). The energy of UHECRs reached up to 1015 eV [1, 2]. In this time energy of particles produced in laboratories was at the level of 107 eV. In 1962, Linsley at Volcano Ranch recorded an air shower from a cosmic ray with giant energy higher than 1020 eV [3]. In 1965, Penzias and Wilson discovered the cosmic microwave background (CMB) radiation. This discovery overshadowed Linsley's experiment, the fantastically huge cosmic ray energy did not receive any attention that it deserved. Just after CMB discovery, **G**reisen, **Z**atsepin, and **K**uzmin (GZK) [4, 5] predicted that photo-pion production by the CMB photons reduces the path length for protons of UHECRs. In the rest frame of proton, the CMB is a beam of very energetic photons. The GZK threshold is the cosmic ray energy at which a Lorentz-boosted CMB photon has energy equal to the pion rest energy. The Planck distribution of CMB photons causes pion photo-production energy loss for protons with energies above approximately 7 × 1019 eV. The effect predicts that the spectrum from distributed homogeneous sources in the universe is suppressed above the GZK

threshold at least one order of magnitude compared to the flux without the GZK effect.

particles that are produced in sources throughout the universe.

without a significant improvement in the observations.

If one assumes that the sources accelerate nuclei to a maximum energy above the energy threshold for photo-disintegration on CMB photons, the light elements could then be fragments of heavier nuclei that disintegrated during propagation. Candidate air shower primary particles all suffer severe propagation losses that should produce an effective cut-off at ≤10<sup>20</sup> eV in experiments so far, assuming only that high-energy cosmic rays are normal

At the moment, the UHECRs remain a puzzle. Reliable conclusions from measurements of the energy spectrum, composition, and anisotropy and the proposed models cannot be obtained

**Introductory Chapter: Ultrahigh-Energy Cosmic Rays**

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.79535

Zbigniew Szadkowski

**1. Introduction**

Additional information is available at the end of the chapter

Zbigniew SzadkowskiAdditional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79535

#### **Introductory Chapter: Ultrahigh-Energy Cosmic Rays Introductory Chapter: Ultrahigh-Energy Cosmic Rays**

DOI: 10.5772/intechopen.79535
