Dobivanje amplitude pionske raspodjele iz mjerenja CLEO i E791

Using QCD perturbation theory in NLO and light-cone QCD sum rules, we extract from the CLEO experimental results the data on the Fγ ∗γπ (Q2) transition form factor constraints, on the Gegenbauer coefficients a2 and a4, as well as on the inverse moment (x −1)π of the pion distribution amplitude. We show that both the asymptotic and the Chernyak–Zhitnitsky pion distribution amplitudes are excluded at the 3σ- and 4σ-level, respectively, while the data confirm the end-point suppressed shape of the pion DA that we previously obtained with QCD sum rules and nonlocal condensates. These findings are also supported by the data of the Fermilab E791 experiment on diffractive di-jet production.Primjenom teorije smetnje QCD u blizu-vodećem redu i zbrojnih pravila QCD, iz podataka mjerenja CLEO o prijelaznom faktoru oblika za Fγ ∗γπ (Q2) , izvodimo ograničenja na Gegenbauerove koeficijente a2 i a4, kao i na inverzni moment amplitude pionske raspodjele (x −1)π. Pokazujemo da su asimptotska i Chernyak– Zhitnitskyjeva amplituda pionske raspodjele isključene na razini 3σ odn. 4σ, dok podaci potvrđuju potisnuti oblik kraja pionske distribucijske amplitude izvedene zbrojnim pravilima QCD i nelokalnim kondenzatima. Naše zaključke podržavaju također mjerenja difraktivne tvorbe dvojnih mlazova E791 u Fermilabu

Resummation Approach in QCD Analytic Perturbation Theory

We discuss the resummation approach in QCD Analytic Perturbation Theory (APT). We start with a simple example of asymptotic power series for a zero-dimensional analog of the scalar $g\,\phi^4$ model. Then we give a short historic preamble of APT and show that renormgroup improvement of the QCD perturbation theory dictates to use the Fractional APT (FAPT). After that we discuss the (F)APT resummation of nonpower series and provide the one-, two-, and three-loop resummation recipes. We show the results of applications of these recipes to the estimation of the Adler function $D(Q^2)$ in the $N_f=4$ region of $Q^2$ and of the Higgs-boson-decay width $\Gamma_{H\to b\bar{b}}(m_H^2)$ for $M_H=100-180$ GeV$^2$.Comment: 8 pages, 2 Figures, 3 Tables. Talk presented by the first author at the International HADRON STRUCTURE'11 Conference, Tatranska Strba (Slovakia), June 27--July 1, 2011 and also at the International Conference "NEW TRENDS IN HIGH-ENERGY PHYSICS (experiment, phenomenology, theory)", Alushta, Crimea, Ukraine, September 3--10, 201

Dobivanje amplitude pionske raspodjele iz mjerenja CLEO i E791

Using QCD perturbation theory in NLO and light-cone QCD sum rules, we extract from the CLEO experimental results the data on the Fγ ∗γπ (Q2) transition form factor constraints, on the Gegenbauer coefficients a2 and a4, as well as on the inverse moment (x −1)π of the pion distribution amplitude. We show that both the asymptotic and the Chernyak–Zhitnitsky pion distribution amplitudes are excluded at the 3σ- and 4σ-level, respectively, while the data confirm the end-point suppressed shape of the pion DA that we previously obtained with QCD sum rules and nonlocal condensates. These findings are also supported by the data of the Fermilab E791 experiment on diffractive di-jet production.Primjenom teorije smetnje QCD u blizu-vodećem redu i zbrojnih pravila QCD, iz podataka mjerenja CLEO o prijelaznom faktoru oblika za Fγ ∗γπ (Q2) , izvodimo ograničenja na Gegenbauerove koeficijente a2 i a4, kao i na inverzni moment amplitude pionske raspodjele (x −1)π. Pokazujemo da su asimptotska i Chernyak– Zhitnitskyjeva amplituda pionske raspodjele isključene na razini 3σ odn. 4σ, dok podaci potvrđuju potisnuti oblik kraja pionske distribucijske amplitude izvedene zbrojnim pravilima QCD i nelokalnim kondenzatima. Naše zaključke podržavaju također mjerenja difraktivne tvorbe dvojnih mlazova E791 u Fermilabu

Unbiased analysis of CLEO data at NLO and pion distribution amplitude

We discuss different QCD approaches to calculate the form factor F^{\gamma^*\gamma\pi}(Q^2) of the \gamma^*\gamma\to\pi^{0} 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^{\gamma^*\gamma\pi}(Q^{2}) by Schmedding and Yakovlev. Special attention is paid to the sensitivity of the results to the (strong radiative) \alpha_s-corrections and to the value of the twist-four coupling \delta^2. We present a full analysis of the CLEO data at the NLO level of LCSRs, focusing particular attention to the extraction of the relevant parameters to determine the pion distribution amplitude, i.e., the Gegenbauer coefficients a_2 and a_4. 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 non-locality parameter \lambda^2_q = / =0.4 GeV^2, which specifies the average virtuality of the vacuum quarks.Comment: 25 pages, 5 figures, 4 tables; format and margins corrected to fit page size; small changes in the text and correction of misprint