Air shower (physics)

Air shower formation in the atmosphere. First proton collides with a particle in the air creating pions, protons and neutrons.

After the primary cosmic particle has collided with the air molecule, the main part of the first interactions are pions. Also kaons and baryons may be created. Pions and kaons are not stable, thus they may decay into other particles.

The neutral pions ${\displaystyle \pi ^{0}}$ decay into photons ${\displaystyle \gamma }$ in a process ${\displaystyle \pi ^{0}\rightarrow \gamma +\gamma }$. The photons produced form an electromagnetic cascade by creating more photons, protons, antiprotons, electrons and positrons.[2]

The charged pions ${\displaystyle \pi ^{\pm }}$ preferentially decay into muons and neutrinos in the processes ${\displaystyle \pi ^{+}\rightarrow \mu ^{+}+\nu }$ and ${\displaystyle \pi ^{-}\rightarrow \mu ^{-}+\nu }$. This is how the muons and neutrinos are produced in the air shower.[2]

The same holds true for kaons which can produce muons in the process ${\displaystyle K^{+/-}\rightarrow \mu ^{+/-}+\nu }$. In addition, kaons can produce also pions via the decay mode ${\displaystyle K^{+/-}\rightarrow \pi ^{+/-}+\pi ^{0}}$.[2]

The 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. In addition, the secondary particles produce a widespread flash of light in forward direction due to the Cherenkov effect, as well as fluorescence light that is emitted isotropically from the excitation of nitrogen molecules. The particle cascade and the light produced in the atmosphere can be detected with surface detector arrays and optical telescopes. Surface detectors typically use Cherenkov detectors or Scintillation counters to detect the charged secondary particles at ground level. The telescopes used to measure the fluorescence and Cherenkov light use large mirrors to focus the light on PMT clusters. 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.

The longitudinal profile of the number of charged particles can be parameterized by the Gaisser–Hillas function.

• Cosmic-ray observatory

• Extensive Air Showers.
• Buckland Park Air Shower Detector
• Haverah Park Detection System
• HiRes Detector System
• Pierre Auger Observatory
• HiSPARC (High School Project on Astrophysics Research with Cosmics)
• AIRES (AIRshower Extended Simulations) : Large and well documented Fortran package for simulating cosmic ray showers by Sergio Sciutto at the Department of Physics of the Universidad Nacional de La Plata, Argentina
• CORSIKA, CORSIKA: Another code for simulating cosmic ray air showers by Dieter Heck of the Forschungszentrum Karlsruhe, Germany
• COSMUS : Interactive animated 3d models of several different cosmic ray air showers, and instructions on how to make your own using AIRES simulations. From the COSMUS group at the University of Chicago.
• Milagro Animations : Movies and instructions for how to make them, showing how air showers interact with the Milagro detector. By Miguel Morales.
• CASSIM Animations : Animations of different cosmic ray air showers by Hajo Dreschler of New York University.
• SPASE2 Experiment : South-Pole Air Shower Experiment (SPASE).
• GAMMA Experiment : High mountain Air Shower Experiment.