k-meson

(particle physics) Collective name for four pseudo-scalar mesons, having masses of about 495 MeV (megaelectronvolts) and decaying via weak interactions: K⁺, K^-, K0S, and K0L; they consist of two isotopic spin doublets, the (K⁺, K⁰) doublet and its antiparticle doublet (K^-, &Kmacr;⁰), having hypercharge or strangeness of +1 and -1 respectively, where K⁰ and &Kmacr;⁰ are certain combinations of K_L⁰ and K_S⁰ states. Also known as kaon. Collective name for any meson resonance belonging to an isotopic doublet with hypercharge +1 or -1, denoted K_JP(m) or &Kmacr;_JP(m) respectively, where m is the mass in megaelectronvolts, and J and P are the spin and parity.

The noun has one meaning:

Meaning #1: an unstable meson produced as the result of a high-energy particle collision
  Synonyms: kaon, kappa-meson, K particle