Extending the application of the LCSR method to low momenta using QCD renormalization-group summation. Theory and phenomenology
| Autor: | Mikhailov, S. V., Pimikov, A. V., Stefanis, N. G. |
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| Rok vydání: | 2021 |
| Předmět: | |
| Zdroj: | Phys. Rev. D 103, 096003 (2021) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevD.103.096003 |
| Popis: | We show that using renormalization-group summation to generate the QCD radiative corrections to the $\pi-\gamma$ transition form factor, calculated with lightcone sum rules (LCSR), renders the strong coupling free of Landau singularities while preserving the QCD form-factor asymptotics. This enables a reliable applicability of the LCSR method to momenta well below 1 GeV$^2$. This way, one can use the new preliminary BESIII data with unprecedented accuracy below 1.5 GeV$^2$ to fine tune the prefactor of the twist-six contribution. Using a combined fit to all available data below 3.1 GeV$^2$, we are able to determine all nonperturbative scale parameters and a few Gegenbauer coefficients entering the calculation of the form factor. Employing these ingredients, we determine a pion distribution amplitude with conformal coefficients $(b_2,b_4)$ that agree at the $1\sigma$ level with the data for $Q^2 \leqslant 3.1$ GeV$^2$ and fulfill at the same time the lattice constraints on $b_2$ at N$^3$LO together with the constraints from QCD sum rules with nonlocal condensates.The form-factor prediction calculated herewith reproduces the data below 1 GeV$^2$ significantly better than analogous predictions based on a fixed-order power-series expansion in the strong coupling constant. Comment: 15 pages, 3 figures, 1 table, [v3] reformatted in two-column style, 15 pages; references added, typos corrected, [v4] minor corrections |
| Databáze: | arXiv |
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