Pseudovector meson

In high energy physics, a pseudovector meson or axial vector meson is a meson with total spin 1 and even parity (+) (usually noted as J^ P = 1^+ ). Compare to a vector meson, which has a total spin 1 and odd parity (that is, J^ P = 1^− ). The known pseudovector mesons fall into two different classes, all have even spatial parity ( P = "+" ), but they differ in another kind of parity called charge parity (C) which can be either even (+) or odd (−). The two types of pseudovector meson are: those with odd charge parity J^ PC = 1^+− those with even charge parity J^ PC = 1^++ The 1^+− group has no intrinsic spin excitation ( S = 0 ), but do gain spin from angular momentum ( L = 1 ) of the orbits of the two constituent quarks around their mutual center. The second group (1^++) have both intrinsic spin S = 1 , and L = 1 , with L and S coupling to J = 1 . Pseudovector, or axial vector, mesons in the 1^+− category are most readily be seen in proton‐antiproton annihilation and pion‐nucleon scattering. The mesons in the 1^++ category are normally seen in proton-proton and pion-nucleon scattering. The difference between the two groups gives them slightly different masses, from the spin‐orbit coupling rule. Theoretically, the h and b mesons are in the 1^+− group, and should have heavier masses, according to the spin-orbit mass splitting. However, the measured masses of the mesons do not appear to follow the rule, as evidenced by the f and a mesons being heavier. There are considerable uncertainties in experimental measurement of pseudovector mesons; more experimental data will be needed to confirm and accurately determine the discrepancy between theory and measurement. The 1^++ multiplet of light mesons may show similar behavior to that of other vector mesons, in that the mixing of light quarks with strange quarks appears to be small for this quantum number. The 1^+− multiplet, on the other hand, may be affected by other factors that generally reduce meson masses. Again, further experimentation is required in order to solidify the observations.

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Scalar meson

In high energy physics, a scalar meson is a meson with total spin 0 and even parity (usually noted as JP=0+). Compare to pseudoscalar meson. The first known scalar mesons have been observed since the late 1950s, with observations of numerous light states and heavier states proliferating since the 1980s. Scalar mesons are most often observed in proton-antiproton annihilation, radiative decays of vector mesons, and meson-meson scattering.

Vector meson

In high energy physics, a vector meson is a meson with total spin 1 and odd parity (usually noted as JP = 1−). Vector mesons have been seen in experiments since the 1960s, and are well known for their spectroscopic pattern of masses. The vector mesons contrast with the pseudovector mesons, which also have a total spin 1 but instead have even parity. The vector and pseudovector mesons are also dissimilar in that the spectroscopy of vector mesons tends to show nearly pure states of constituent quark flavors, whereas pseudovector mesons and scalar mesons tend to be expressed as composites of mixed states.

Pseudovector meson

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