Identify the dominant decay channels of the a_1(1640)

Identify the dominant decay channels of the a_1(1640) axial-vector resonance in order to determine an experimentally grounded lineshape for its contribution to the nucleon axial form factor.

Background

The dispersive reconstruction models the a_1(1640) resonance using a rho-pion decay channel because the available experimental information is limited. The assumed channel may not be reliable: the rho-prime-pion channel could be important, and the broad rho(1450) makes a realistic lineshape difficult to construct. Establishing the dominant decay channels would therefore reduce a central modeling uncertainty in the resonance contribution.

References

By contrast to the $a_1(1260)$, which is well-known from $\tau\to3\pi$ decays, the experimental information for the $a_1(1640)$ is scarce, and even its main decay channels remain unknown.

— The axial-vector nucleon form factor in the meson dominance picture: the role triangle singularities from a dispersive view  (2609.05109 - Arriola et al., 4 Sep 2026) in Section 5, subsection “Resonances below N \bar N”