Two-pole structure of the b1 (1235) axial-vector meson

초록

We investigate the dynamical generation of the b1 meson in the πω interaction, using a coupled-channel formalism with the πω, ηρ, πφ, and KK̄∗ channels included. We compute the Feynman amplitudes for the 16 different kernel amplitudes, considering only the t and u channels. Solving the coupled integral equation, we obtain the transition amplitude for the πω interaction. We select the axial-vector and isovector channels from the partial-wave expansion and single out the two poles corresponding to the b1 mesons: (1306-i70) MeV and (1356-i65) MeV. They are located below the KK̄∗ threshold. The first pole lies below the ηρ threshold by about 10 MeV, whereas the second one emerges above it by about 40 MeV. We analyze the effects of the two poles and background contributions to the πω total cross section by using a toy model.

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