COSMIC RAYS, SUBATOMIC PARTICLES AND MORE...
COSMIC RAYS
Cosmic rays are high-energy radiation, mainly originating outside the Solar System and even from distant galaxies. Upon impact with the Earth's atmosphere, cosmic rays can produce showers of secondary particles that sometimes reach the surface, like muons.
Of primary cosmic rays, originated outside of Earth's atmosphere, about 99% are the nuclei of well-known atoms, and about 1% are solitary electrons. Of the nuclei, about 90% are simple protons (i.e., hydrogen nuclei); 9% are alpha particles, identical to helium nuclei; and 1% are the nuclei of heavier elements, called HZE ions. A very small fraction are stable particles of antimatter, such as positrons or antiprotons.
PIONS
A pion consists of a quark and an antiquark and is, therefore, a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions π+ and π− decaying with a mean lifetime of 26.033 nanoseconds, and the neutral pion π0 decaying with a much shorter lifetime of 8.4×10−17 seconds. Charged pions most often decay into muons and muon neutrinos, while neutral pions generally decay into gamma rays.
The exchange of virtual pions, along with other mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but are commonly produced in high energy accelerators in collisions between hadrons. All types of pions are also produced in natural processes when high energy cosmic rays interact with matter in the Earth's atmosphere. Recently, the detection of characteristic gamma rays has shown that pions are produced copiously after supernovas, in conjunction with the production of high energy protons that are detected on Earth as cosmic rays.
MUONS
The muon is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton. As such, the muon is not believed to be composed of any simpler particles.
The muon is an unstable subatomic particle with a mean lifetime of 2.2 μs, much longer than many other subatomic particles. Muon decay is slow (by subatomic standards) because the decay is mediated by the weak interaction exclusively (rather than the more powerful strong interaction or electromagnetic interaction), and because the mass difference between the muon and the set of its decay products is small.
Muons appear on Earth as the result of the decay of secondary cosmic rays, which is supposed to happen at around 15 km above the surface. If muons were to travel at the speed of light 3.000.000 m/s (which they do not), they would only travel 600 m, not reaching the surface. However, since they travel at speeds closer to the speed of light
Muon decay almost always produces at least three particles, which must include an electron of the same charge as the muon and two neutrinos of different types.