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In particle physics, a pion (/ ˈ p aɪ. ɒ n /, PIE-on) or pi meson, denoted with the Greek letter pi (π), is any of three subatomic particles: π 0, π +, and π −. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the ...
The intrinsic parity of the pion is P = −1 (since the pion is a bound state of a quark and an antiquark, which have opposite parities, with zero angular momentum), and parity is a multiplicative quantum number. Therefore, assuming the parent particle has zero spin, the two-pion and the three-pion final states have different parities (P = +1 ...
Mesons named with the letter "f" are scalar mesons (as opposed to a pseudo-scalar meson), and mesons named with the letter "a" are axial-vector mesons (as opposed to an ordinary vector meson) a.k.a. an isoscalar vector meson, while the letters "b" and "h" refer to axial-vector mesons with positive parity, negative C-parity, and quantum numbers I G of 1 + and 0 − respectively.
For example, a positive pion (π +) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion (π −), is made of one up antiquark and one down quark. Because mesons are composed of quarks, they participate in both the weak interaction and strong interaction.
A quark (/ k w ɔːr k, k w ɑːr k /) is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. [1] All commonly observable matter is composed of up quarks, down quarks and electrons.
Despite the pseudoscalar mesons' masses being known to high precision, and being the most well studied and understood mesons, the decay properties of the pseudoscalar mesons, particularly of eta (η) and eta-prime (η ′), are somewhat contradictory to their mass hierarchy: While the η ′ meson is much more massive than the η meson, the η meson is thought to contain a larger component of ...
These rules are described by quantum chromodynamics (QCD), the theory of quark–gluon interactions. Unlike the photon in electromagnetism, which is neutral, the gluon carries a color charge. Quarks and gluons are the only fundamental particles that carry non-vanishing color charge, and hence they participate in strong interactions only with ...
Subsequently, the decays into a proton and another negative pion. In general this is the signature of the decay of a Ξ {\displaystyle \Xi } . Although the negative Ω {\displaystyle \Omega } (sss) baryon has a similar final state decay topology, it can be clearly distinguished from the Ξ {\displaystyle \Xi } because its decay products are ...