On the theoretical side, the milestones for the second funding period are:
- Study of dispersive analyses of the γ*γ → ππ and γ*γ*→ ππ processes in support of the experimental program at BESIII, and an exploratory study of their extensions to π0η, ηη, K+K- and K0K̅0 final states
- Implementation of the 2π channel into the dispersive theory for the HLbL contribution to aμ.
- Study of doubly virtual meson TFFs and application to the P → e+e- decay
- Application of light-by-light sum rules to charmonium states
For the BESIII γγ program, the milestones for the second funding period are:
- High statistics single-tag measurements at BESIII of the pseudoscalar meson transition FFs. For η and η' this will correspond with an order of magnitude increase in statistics over existing measurements.
- Measurement of the spacelike γ*γ → π+π- process at BESIII
- Measurement of the spacelike γ*γ → π0π0, π0η processes at BESIII
- Exploratory study of the spacelike double-off-shell TFF γ*γ → π0 at BESIII
- Hardware Project: Design study of a new Zero Degree Tagging Detector (ZDD) for BESIII
The experimental program at BESIII will be complemented by experiments at MAMI using the Crystal Ball, of which the milestones in the second funding period are:
- Measurement of the timelike η' TFF in the decay η' → e+e-γ with Crystal Ball/TAPS
- Exploratory study of the timelike TFF measurements in the decays π0 → e+e-γ at Crystal Ball/TAPS