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.

The known pseudovector, or axial vector, mesons fall into two different classes; those with J^PC = 1⁺⁻, and those with J^PC = 1⁺⁺. The first group have no spin excitation, but do have L = 1. The latter group have both S = 1 and L = 1, with L and S coupling to J = 1. The difference between the two groups gives them slightly different masses from the spin-orbit coupling rule. The h and b mesons are in the first group, and should have heavier masses according to the spin-orbit mass splitting; in practice, however, they do not appear to follow this rule in nature, as evidenced by the f and a mesons being heavier. There are considerable experimental uncertainties in pseudovector meson masses which will require additional experimental data to clarify.

The 1⁺⁺ multiplet of light mesons may show similar behavior to that of the 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 cause generally reduced meson masses. Further experimentation is required in order to clarify the observed situation.

Pseudovector, or axial vector, mesons in the 1⁺⁻ channel may most readily be seen in proton-antiproton annihilation and pion-nucleon scattering. The mesons in the 1⁺⁺ channel are normally seen in proton-proton and pion-nucleon scattering.

Examples

• 1⁺⁻ candidates: h₁(1170), b₁(1235), h₁(1380)
• 1⁺⁺ candidates: f₁(1285), a₁(1260), f₁(1420)
• strange candidates: K₁(1270), K₁(1400)
• heavy candidates: h_c, χ_c1

See also

• List of mesons