Virtuality Distributions in application to gamma gamma* to pi^0 Transition Form Factor at Handbag Level

Journal Article · Tue Jul 01 00:00:00 EDT 2014 · Physics Letters. Section B

DOI:https://doi.org/10.1016/j.physletb.2014.06.078· OSTI ID:1136734

Radyushkin, Anatoly V. ^[1]

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1. ODU, JLAB

We outline basics of a new approach to transverse momentum dependence in hard processes. As an illustration, we consider hard exclusive transition process gamma*gamma -> to pi^0 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 z^2, they are parametrized through a virtuality distribution amplitude (VDA) Phi (x, sigma), with x being Fourier-conjugate to (pz) and sigma Laplace-conjugate to z^2. For intervals with z^+=0, we introduce transverse momentum distribution amplitude (TMDA) Psi (x, k_\perp), and write it in terms of VDA Phi (x, \sigma). The results of covariant calculations, written in terms of Phi (x sigma) are converted into expressions involving Psi (x, k_\perp. 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_\perp tails from primordial soft distributions.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1136734
• Report Number(s): JLAB-THY-14-1873; DOE/OR/23177-3048; arXiv:1404.7032; FG02-97ER41028
• Journal Information: Physics Letters. Section B, Vol. 735; ISSN 0370-2693
• Publisher: Elsevier
• Country of Publication: United States
• Language: English