Light-front approach to axial-vector quarkonium γ * γ * form factors

In this work, we perform a detailed study of transition form factors for axial- vector meson production via the two-photon fusion process γ * γ * → 1 ++ , with space-like virtual photons in the initial state and a P -wave axial-vector quarkonium in the final state. In this analysis, we employ the formalism of light-front quarkonium wave functions obtained from a solution of the Schrödinger equation for a selection of interquark potentials for QQ interaction. We found the helicity structure and covariant decomposition of the matrix elements that can be generically applied for any qq axial-vector meson γ * γ * → 1 ++ transition, while our numerical results are given for the phenomenologically relevant charmonium χ c 1 state. We present the helicity form factors as functions of both photon virtualities. We also obtain, that QF LT ( Q 2 , 0) /F TT ( Q 2 , 0) = const .