Towards an improved understanding of $a_1$ and $a_2$ transition form factors

10 Jun 2026, 12:00
20m
Scuola Normale Superiore, Aula Dini, Palazzo del Castelletto (Pisa)

Scuola Normale Superiore, Aula Dini, Palazzo del Castelletto

Pisa

Via del Castelletto, 11, 56126 Pisa PI

Speaker

Hannah Schäfer (Bern University)

Description

The isovector axial-vector and tensor meson states $a_1$ and $a_2$ have garnered interest in the last years since they appear as intermediate states in the hadronic light-by-light (HLbL) scattering contribution to $(g-2)_\mu$. Their dynamical behaviour, including their transition form factors, is poorly understood to this day, which also affects the uncertainty budget of the HLbL contribution.
In order to improve the situation, we construct the $a_1$ and $a_2$ as resonances in the $\rho \pi$ system, which allows us to express the relevant amplitudes in terms of known form factors. However, imaginary parts and singularities in this system need to be understood. With this, we aim to obtain a phenomenologically well motivated parameterisation of the transition form factors.

Are you an early career researcher? Yes, a Postdoc

Authors

Dr Bastian Kubis (Universität Bonn) Eirini Lymperiadou (PSI Villigen) Hannah Schäfer (Bern University) Dr Pablo Sánchez-Puertas (Universidad de Granada)

Presentation materials