806 research outputs found
Axial-vector transition form factors and
We study the transition form factors (TFFs) of axial-vector mesons in the
context of currently available experimental data, including new constraints
from that imply stringent limits on the
high-energy behavior and, for the first time, allow us to provide an
unambiguous determination of the couplings corresponding to the two
antisymmetric TFFs. We discuss how these constraints can be implemented in a
vector-meson-dominance picture, and, in combination with contributions from the
light-cone expansion, construct TFFs as input for the evaluation of
axial-vector contributions to hadronic light-by-light scattering in the
anomalous magnetic moment of the muon.Comment: 28 pages, 4 figures; journal versio
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On the transition form factors of the axial-vector resonance and its decay into
Estimating the contribution from axial-vector intermediate states to hadronic
light-by-light scattering requires input on their transition form factors
(TFFs). Due to the Landau-Yang theorem, any experiment sensitive to these TFFs
needs to involve at least one virtual photon, which complicates their
measurement. Phenomenologically, the situation is best for the
resonance, for which information is available from ,
, , , and .
We provide a comprehensive analysis of the TFFs in the framework of
vector meson dominance, including short-distance constraints, to determine to
which extent the three independent TFFs can be constrained from the available
experimental input, a prerequisite for improved calculations of the
axial-vector contribution to hadronic light-by-light scattering. In particular,
we focus on the process , evidence for which has been reported
recently by SND for the first time, and discuss the impact that future improved
measurements will have on the determination of the TFFs.Comment: 60 pages, 14 figures; v2: Appendix D on alternative
mechanism added, references updated, version published in JHE
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