Introduction to HECRs Phenomenology, Observations, and Open Questions - Lecture 1

Explore the fundamental aspects of High-Energy Cosmic Rays (HECRs) in this comprehensive lecture delivered by Rafael Alves-Batista from IAP, France, as part of the CLAF/ICTP-SAIFR Latin-American Astroparticle Physics School. Delve into the phenomenology of these ultra-high-energy particles that bombard Earth from outer space, examining their observed characteristics and the sophisticated detection methods used to study them. Learn about the current state of HECR observations, including energy spectra, arrival directions, and composition measurements from major observatories worldwide. Investigate the key open questions that continue to challenge researchers in the field, such as the origins of these particles, their acceleration mechanisms, and the astrophysical sources capable of producing such extreme energies. Gain insights into the theoretical frameworks used to understand HECR propagation through intergalactic space and the interactions that modify their properties during their journey to Earth. This foundational lecture provides essential background knowledge for understanding one of the most energetic phenomena in the universe and sets the stage for advanced studies in astroparticle physics.