Kaon in the context of Strangeness (particle physics)

Air showers are extensive cascades of subatomic particles and ionized nuclei, produced in the atmosphere when a primary cosmic ray enters the atmosphere. Particles of cosmic radiation can be protons, nuclei, electrons, photons, or (rarely) positrons. Upon entering the atmosphere, they interact with molecules and initiate a particle cascade that lasts for several generations, until the energy of the primary particle is fully converted. 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. Primary photons and electrons, on the other hand, produce mainly electromagnetic showers. 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 unwittingly 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.

The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons (K), strange D mesons (D
_s), sigma baryons (Σ), and other strange particles.

According to the IUPAP, the symbol s is the official name, while "strange" is to be considered only as a mnemonic. The name sideways has also been used because the s quark (but also the other three remaining quarks) has an I₃ value of 0 while the u ("up") and d ("down") quarks have values of +⁠1/2⁠ and −⁠1/2⁠ respectively.

In high-energy physics, a pseudoscalar meson is a meson with total spin 0 and odd parity (usually notated as J = 0 ).Pseudoscalar mesons are commonly seen in proton–proton scattering and proton–antiproton annihilation, and include the pion (π), kaon (K), eta (η), and eta prime (η′) particles, whose masses are known with great precision.

Among all of the mesons known to exist, in some sense, the pseudoscalars are the most well studied and understood.

In particle physics, a rho meson is a short-lived hadronic particle that is an isospin triplet whose three states are denoted as ρ
, ρ
and ρ
. Along with pions and omega mesons, the rho meson carries the nuclear force within the atomic nucleus. After the octet consisting of the pions, kaons, and eta meson, the rho mesons are the lightest strongly interacting particle, with a mass of about 775 MeV for all three states.

The rho mesons have a very short lifetime and their decay width is about 145 MeV; because that is large compared with the mass, the resonance width measurably deviates from a Breit–Wigner form. The principal decay route of the rho mesons is to a pair of pions with a branching rate of 99.9% (however, all neutral pions is forbidden).