Kmeson

K meson, or kaon, is a meson that contains a strange quark or antiquark. It is a spin-0 pseudoscalar hadron. The lightest kaons form a family of four: K+, K-, K0, and anti-K0. Their quark contents are K+ = u s̄, K- = ū s, K0 = d s̄, and anti-K0 = s d̄. Charged kaons carry electric charge ±1, while neutral kaons are neutral. Kaons are produced in high-energy hadron collisions and in cosmic-ray interactions, and they decay weakly with lifetimes ranging from about 10^-8 to 10^-10 seconds.

In the neutral kaon system, K0 and anti-K0 can transform into each other via second-order weak interactions. The observable states are the mass eigenstates KS and KL, with lifetimes of about 0.089 nanoseconds and 50 nanoseconds, respectively. KS decays predominantly to two pions, while KL decays mainly to three pions or semileptonic final states.

The neutral kaon system was central to the discovery of CP violation in 1964, observed in KL decays to two pions. CP violation in kaons is described by parameters such as epsilon and epsilon prime and provides important tests of the Standard Model and constraints on the CKM matrix.

Kaons remain important probes of flavor physics, weak interactions, and fundamental symmetries, with ongoing studies of decay rates, semileptonic processes, and CPT invariance.