Physics Letters B
We outline basics of a new approach to transverse momentum dependence in hard processes. As an illustration, we consider hard exclusive transition process ɣ*ɣ -> π0 at the handbag level. Our starting point is coordinate representation for matrix elements of operators (in the simplest case, bilocal O(0, z)) describing a hadron with momentum p. Treated as functions of (pz) and z2, they are parametrized through virtuality distribution amplitudes (VDA) Φ(x, σ), with x being Fourier-conjugate to (pz) and σ Laplace-conjugate to z2. For intervals with z+ = 0, we introduce the transverse momentum distribution amplitude (TMDA) Ѱ(x, k┴), and write it in terms of (VDA) Φ(x, σ). The results of covariant calculations, written in terms of Φ(x, σ) are converted into expressions involving Ѱ(x, k┴) Starting with scalar toy models, we extend the analysis onto the case of spin-1/2 quarks and QCD. We propose simple models for soft VDAs/TMDAs, and use them for comparison of handbag results with experimental (BaBar and BELLE) data on the pion transition form factor. We also discuss how one can generate high-k┴ tails from primordial soft distributions.
Original Publication Citation
Radyushkin, A. V. (2014). Virtuality distributions in application to ɣɣ* → π0 transition form factor at handbag level. Physics Letters B, 735, 417-425. doi: 10.1016/j.physletb.2014.06.078
Radyushkin, Anatoly V., "Virtuality Distributions in Application to ɣɣ* → π0 Transition Form Factor at Handbag Level" (2014). Physics Faculty Publications. 54.