Mesonen

Mesonen, known in English as mesons, are a class of hadrons composed of a quark and an antiquark bound together by the strong interaction. In Dutch, the plural form is mesonen. Mesonen are bosons with integer spin and span a wide range of masses, from the light pions to heavy quarkonia. All mesonen are color singlets, and their properties are described by quantum chromodynamics and quark models. A meson’s quark content is written as q anti-q, where q can be any of the light or heavy quark flavors (up, down, strange, charm, bottom); the top quark does not form bound mesons because it decays too quickly.

Mesonen are classified by their quantum numbers and quark content. The lightest mesonen are the pions (π+, π0, π−) and the kaons (K+, K0 and their antiparticles). Pions play a central role in mediating the residual strong force between nucleons in early nuclear-force models. Heavier mesonen include charm-containing D mesons, bottom-containing B mesons, and quarkonia states such as J/ψ (charmonium) and Υ (bottomonium), which are bound pairs of a heavy quark and its antiquark. Mesonen can have various total angular momentum J and parity P, with common light states often having J^P = 0− or 1−.

Most mesonen are unstable and decay via strong, electromagnetic, or weak interactions, with lifetimes ranging from about 10^-23 seconds (for strong decays) to around 10^-10 seconds or longer (for weak decays). The study of mesonen, part of hadron spectroscopy, tests quantum chromodynamics and informs models of quark confinement. The concept and experimental verification of mesonen emerged in the mid-20th century, consistent with Yukawa’s theory of the nuclear force.