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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.
The latter are called scalar mesons or pseudoscalar mesons, depending on their parity (see below). There is another quantity of quantized angular momentum , called the orbital angular momentum (quantum number L ), that is the angular momentum due to quarks orbiting each other, and also comes in increments of 1 ħ .
Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles. [1] They are the fundamental objects of quantum field theory. Many families and sub-families of elementary particles exist. Elementary particles are classified according to their spin.
A strange particle is an elementary particle with a strangeness quantum number different from zero. Strange particles are members of a large family of elementary particles carrying the quantum number of strangeness , including several cases where the quantum number is hidden in a strange/anti-strange pair, for example in the ϕ meson .
The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons (K), strange D mesons (D s), Sigma baryons (Σ), and other strange particles.
It was thought that the initial states should also have different parities, and hence be two distinct particles. However, with increasingly precise measurements, no difference was found between the masses and lifetimes of each, respectively, indicating that they are the same particle. This was known as the τ–θ puzzle.
Like all particle states, exotic mesons are specified by the quantum numbers which label representations of the Poincaré symmetry, q.e., by the mass (enclosed in parentheses), and by J PC, where J is the angular momentum, P is the intrinsic parity, and C is the charge conjugation parity; One also often specifies the isospin I of the meson.
A multi-quark state of 4 or more quarks (tetraquark, pentaquark, etc.) is also proposed as well as a molecule-like state of multiple mesons. [5] [6] While each of these three types of states have had some success of explaining the newly discovered particle, a complete explanation has not been found.