TFF – Meson transition form factors

Project leaders


We will perform the world's best determination of the pseudoscalar meson transition form factors in the low- and intermediate momentum transfer range. Measurements in the space-like region at BESIII will be complemented by time-like measurements via Dalitz decays at MAMI.

At large momentum transfer, TFFs encode the quark-antiquark wavefunctions (distribution amplitudes) of mesons, and represent fundamental structure information arising from the strong interaction, in analogy with atomic wavefunctions for electromagnetic bound systems. Furthermore, the experimental program for the pseudoscalar meson TFFs will be complemented within the RU by lattice QCD calculations at physical pion mass values.

Furthermore, we will perform the world's best measurements of the photon-photon fusion cross-sections in two- and multi-meson states and provide their interpretation. The experimental program at BESIII will be complemented by dispersive analyses of the photon-photon fusion cross sections, in order to perform a partial-wave analysis of these processes. This will allow for an extraction of pion generalized polarizabilities as well as the first precision extraction of axial-vector meson TFF. The dispersive analyses will provide crucial input to improve on the data-driven evaluation of the HLbL evaluation of the muon \((g-2)\).