2002/12/31 by A. P. Bakulev, С. В. Михайлов, S. V. Mikhailov +1 · 5 citations
Physics and Astronomy · #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ph
paper · pdf · doi:10.1103/physrevd.67.074012
published as Phys.Rev. D67 (2003) 074012 · 25 pages, 5 figures, 4 tables; format and margins corrected to fit page size; small changes in the text and correction of misprints
arxiv created 2003/01/16 · openalex publication_date 2003/04/15 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We discuss different QCD approaches to calculate the form factor F^\ensuremathγ*\ensuremathγ\ensuremathπ(Q2) of the \ensuremathγ*\stackrel\ensuremath→\ensuremathγ\ensuremathπ0 transition giving preference to the light-cone QCD sum rules (LCSR) approach as being the most adequate. In this context we revise the previous analysis of the CLEO experimental data on F^\ensuremathγ*\ensuremathγ\ensuremathπ(Q2) by Schmedding and Yakovlev. Special attention is paid to the sensitivity of the results to the (strong radiative) \ensuremathαs corrections and to the value of the twist-four coupling \ensuremathδ2. We present a full analysis of the CLEO data at the NLO level of LCSRs, focusing particular attention on the extraction of the relevant parameters to determine the pion distribution amplitude, i.e., the Gegenbauer coefficients a2,a4. Our analysis confirms our previous results and also the main findings of Schmedding and Yakovlev: both the asymptotic as well as the Chernyak-Zhitnitsky pion distribution amplitudes are completely excluded by the CLEO data. A novelty of our approach is to use the CLEO data as a means of determining the value of the QCD vacuum nonlocality parameter \ensuremathλq2=〈qD2q〉/〈qq〉=0.4GeV2, which specifies the average virtuality of the vacuum quarks.