K meson

subatomic particle

Also known as: K-meson, kaon

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July 23, 2026

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A K meson, also known as a kaon, is a type of subatomic particle composed of a quark and an antiquark. Discovered in 1947, kaons are unstable and decay rapidly into other particles, with an average lifetime of about 10^-10 seconds. They have a mass roughly half that of a proton and are electrically neutral. The study of K-mesons has been crucial in understanding fundamental physics, including the weak force and the concept of parity violation. Their behavior has also provided evidence for the existence of new quarks, such as the charm quark.12

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meson
K particle
B meson
quantum mechanics - Decay of the kaon

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- annihilation
  K-mesons—which are classified within the hadron group of subatomic particles. Other annihilation reactions also occur. Nucleons (protons and neutrons), for example, annihilate antinucleons (antiprotons and antineutrons), and the energy is also carried away in the form of particles such as pi-mesons and K-mesons and their…
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  K-mesons—which are classified within the hadron group of subatomic particles. Other annihilation reactions also occur. Nucleons (protons and neutrons), for example, annihilate antinucleons (antiprotons and antineutrons), and the energy is also carried away in the form of particles such as pi-mesons and K-mesons and their…
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- antimatter
  …and negative pi-mesons, and the K-meson and the anti-K-meson, plus a long list of baryons and antibaryons. Most of these newly discovered particles have too short a lifetime to be able to combine with electrons. The exception is the positive muon, which, together with an electron, has been observed to…
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  …and negative pi-mesons, and the K-meson and the anti-K-meson, plus a long list of baryons and antibaryons. Most of these newly discovered particles have too short a lifetime to be able to combine with electrons. The exception is the positive muon, which, together with an electron, has been observed to…
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- quantum mechanics
  Decay of the kaon
  The kaon (also called the K⁰ meson), discovered in 1947, is produced in high-energy collisions between nuclei and other particles. It has zero electric charge, and its mass is about one-half the mass of the proton. It is unstable and, once formed, rapidly decays…
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  The kaon (also called the K⁰ meson), discovered in 1947, is produced in high-energy collisions between nuclei and other particles. It has zero electric charge, and its mass is about one-half the mass of the proton. It is unstable and, once formed, rapidly decays…
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- meson
  …the competing decay modes of K-mesons, which occur via the weak force, have led to a better understanding of parity (the property of an elementary particle or physical system that indicates whether its mirror image occurs in nature) and its nonconservation in the weak interaction. CP violation (the violation of…
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  …the competing decay modes of K-mesons, which occur via the weak force, have led to a better understanding of parity (the property of an elementary particle or physical system that indicates whether its mirror image occurs in nature) and its nonconservation in the weak interaction. CP violation (the violation of…
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- parity
  …decay of subatomic particles called K-mesons, the Chinese-born physicists Tsung-Dao Lee and Chen Ning Yang proposed in 1956 that parity is not always conserved. For subatomic particles three fundamental interactions are important: the electromagnetic, strong, and weak
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  …decay of subatomic particles called K-mesons, the Chinese-born physicists Tsung-Dao Lee and Chen Ning Yang proposed in 1956 that parity is not always conserved. For subatomic particles three fundamental interactions are important: the electromagnetic, strong, and weak
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- CP violation
  …in the decay of charged K-mesons into two or three pi-mesons prompted the Chinese-born American theoretical physicists Chen Ning Yang and Tsung-Dao Lee to examine the experimental foundation of parity conservation itself. In 1956 they showed that there was no evidence supporting parity invariance in so-called weak interactions. Experiments conducted…
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  …in the decay of charged K-mesons into two or three pi-mesons prompted the Chinese-born American theoretical physicists Chen Ning Yang and Tsung-Dao Lee to examine the experimental foundation of parity conservation itself. In 1956 they showed that there was no evidence supporting parity invariance in so-called weak interactions. Experiments conducted…
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- quark
  Quark flavours
  …−1/3e) occur as components of K mesons and various other extremely short-lived subatomic particles that were first observed in cosmic rays but that play no part in ordinary matter.
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  …−1/3e) occur as components of K mesons and various other extremely short-lived subatomic particles that were first observed in cosmic rays but that play no part in ordinary matter.
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Val Logsdon Fitch
…decay of subatomic particles called K mesons could violate the general conservation law for weak interactions known as CP symmetry. Those experiments in turn necessitated physicists’ abandonment of the long-held principle of time-reversal invariance. The work done by Fitch and Cronin implied that reversing the direction of time would not…
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…decay of subatomic particles called K mesons could violate the general conservation law for weak interactions known as CP symmetry. Those experiments in turn necessitated physicists’ abandonment of the long-held principle of time-reversal invariance. The work done by Fitch and Cronin implied that reversing the direction of time would not…
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Tsung-Dao Lee
…same particle (now called the K-meson). Because the law of parity conservation prohibits a single particle from having decay modes exhibiting opposite parity, the only possible conclusion was that, for weak interactions at least, parity is not conserved. They suggested experiments to test their hypothesis, and in 1956–57 Chien-Shiung Wu,…
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…same particle (now called the K-meson). Because the law of parity conservation prohibits a single particle from having decay modes exhibiting opposite parity, the only possible conclusion was that, for weak interactions at least, parity is not conserved. They suggested experiments to test their hypothesis, and in 1956–57 Chien-Shiung Wu,…
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Cecil Frank Powell
…of decay of kaons (K-mesons).
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…of decay of kaons (K-mesons).
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