Air shower (physics)

Particles of cosmic radiation can be protons, nuclei, electrons, photons, or (rarely) positrons.If the primary particle is a hadron, mostly light mesons like pions and kaons are produced in the first interactions, which then fuel a hadronic shower component that produces shower particles mostly through pion decay.Depending on the energy of the primary particle, the detectable size of the shower can reach several kilometers in diameter.The air shower phenomenon was unknowingly discovered by Bruno Rossi in 1933 in a laboratory experiment.In 1937 Pierre Auger, unaware of Rossi's earlier report, detected the same phenomenon and investigated it in some detail.He concluded that cosmic-ray particles are of extremely high energies and interact with nuclei high up in the atmosphere, initiating a cascade of secondary interactions that produce extensive showers of subatomic particles.[1][2] The most important experiments detecting extensive air showers today are HAWC, LHAASO, the Telescope Array Project and the Pierre Auger Observatory.In 1933, shortly after the discovery of cosmic radiation by Victor Hess, Bruno Rossi[3] conducted an experiment in the Institute of Physics in Florence, using shielded Geiger counters to confirm the penetrating character of the cosmic radiation.He also noted that the coincidence rate drops significantly for cosmic rays that are detected at a zenith angle below[4] In a publication in 1939, Pierre Auger, together with three colleagues, suggested that secondary particles are created by cosmic rays in the atmosphere, and conducted experiments using shielded scintillators and Wilson chambers on the Jungfraujoch at an altitude of[5] They found that the rate of coincidences reduces with increasing distance of the detectors, but does not vanish, even at high altitudes.Thus confirming that cosmic rays produce air showers of secondary particles in the atmosphere.Based on the idea of quantum theory, theoretical work on air showers was carried between 1935 and 1940 out by many well-known physicists of the time (including Bhabha, Oppenheimer, Landau, Rossi and others), assuming that in the vicinity of nuclear fields high-energy gamma rays will undergo pair-production of electrons and positrons, and electrons and positrons will produce gamma rays by radiation.[6] [7] [8] [9] Work on extensive air showers continued mainly after the war, as many key figures were involved in the Manhattan project.In the 1950s, the lateral and angular structure of electromagnetic particles in air showers were calculated by Japanese scientists Koichi Kamata and Jun Nishimura.The Volcano Ranch experiment, which was built in 1959 and operated by John Linsley, was the first surface detector array of sufficient size to detect ultrahigh-energy cosmic rays.With a footprint of several kilometers, the shower size at the ground was twice as large as any event recorded before, approximately producingFurthermore, it was confirmed that the lateral distribution of the particles detected at the ground matched Kenneth Greisen's approximation[13] of the structure functions derived by Kamata and Nishimura.He suggested to directly observe Cherenkov radiation of the shower particles, and fluorescence light produced by excited nitrogen molecules in the atmosphere.In 1995,[15][circular reference] the latter reported the detection of an ultrahigh-energy cosmic ray with an energy beyond the theoretically expected spectral cutoff.[16] The air shower of the cosmic ray was detected by the Fly's Eye fluorescence detector system and was estimated to contain approximately 240 billion particles at its maximum., decay by the electroweak interaction into pairs of oppositely spinning photons, which fuel the electromagnetic component of the shower.For the sake of simplicity, photons, electrons, and positrons are often treated as equivalent particles in the shower.The energy deposit as a function of the surpassed atmospheric matter, as it can for example be seen by fluorescence detector telescopes, is known as the longitudinal profile of the shower.The image shows the ideal longitudinal profile of showers using different primary energies, as a function of the surpassed atmospheric depthThe original particle arrives with high energy and hence a velocity near the speed of light, so the products of the collisions tend also to move generally in the same direction as the primary, while to some extent spreading sidewise.The particle cascade and the light produced in the atmosphere can be detected with surface detector arrays and optical telescopes.Finally, air showers emit radio waves due to the deflection of electrons and positrons by the geomagnetic field.As advantage over the optical techniques, radio detection is possible around the clock and not only during dark and clear nights.Thus, several modern experiments, e.g., TAIGA, LOFAR, or the Pierre Auger Observatory use radio antennas in addition to particle detectors and optical techniques.