arXiv subjects

Alexander P. Bakulev

Publications and source records attributed to Alexander P. Bakulev.

24 records · Page 2Linked to original sources

arXiv2004

Pion distribution amplitude -- from theory to data (CELLO, CLEO, E-791, JLab F(pi))

In my talk I discuss the theoretical and experimental status of the pion distribution amplitude (DA). I show that the QCD sum rule method with nonlocal condensates (NLC) for the pion DA gives us admissible sets (bunches) of DAs for each value of QCD-vacuum nonlocality parameter λ_q. Comparing these bunches with the new CLEO constraints, obtained in the NLO light-cone sum-rule analysis of γ^*γ\toπ-transition form factor, allows us to fix the value of QCD vacuum nonlocality λ_q^2\simeq0.4 GeV^2. Then I show that the corresponding bunch of pion DAs agrees well with the E791 data on diffractive dijet production and with the JLab F(pi) data on the pion electromagnetic form factor. The latter comparison is made in the framework of analytic perturbation theory with non-power NLO for the pion form factor, where scale-setting ambiguities are strongly reduced already at the NLO level.

hep-ph↗

arXiv2004

Accessing the pion distribution amplitude through the CLEO and E791 data

Using QCD perturbation theory in NLO and light-cone QCD sum rules, we extract from the CLEO experimental data on the F^{γ^*γπ}(Q^{2} transition form factor constraints on the Gegenbauer coefficients a_2 and a_4, as well as on the inverse moment _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 confirms the end-point suppressed shape of the pion DA 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 dijet production.

hep-ph↗

arXiv2003

Mapping out the quark structure of hadrons in QCD

In the context of QCD sum rules with non-local condensates we present a pion distribution amplitude, which is double-humped with its end-points x\to(0,1) strongly suppressed, and show that it matches the CLEO experimental data on the pion-photon transition at the 1σlevel accuracy, being also in compliance with the CELLO data. We also include some comments on the nucleon distribution amplitude and the nucleon evolution equation.

hep-ph↗

arXiv2003

What is this thing called pion distribution amplitude? From theory to data

We discuss the status of the pion distribution amplitude (DA) from analyzing the CLEO experimental data in the context of QCD sum-rule techniques and QCD perturbation theory at the NLO accuracy. The constraints extracted this way for the Gegenbauer coefficients a_2 and a_4 exclude Φ_{CZ} at the 4σlevel, while Φ_{asy} is outside the 3σerror ellipse. These data provide strong support for the type of endpoint-suppressed, double-humped pion DA we derived via QCD sum rules with nonlocal condensates and favor a value of the vacuum quark virtuality λ_q^2 \simeq 0.4 GeV^2. This pion DA is in agreement with the E791 data, though these experimental results should be viewed carefully and further confirmation is necessary for a more accurate judging of pion DAs from them.

hep-ph↗

arXiv2003

CLEO and E791 data: A smoking gun for the pion distribution amplitude?

The CLEO experimental data on the $πγ$ transition are analyzed to next-to-leading order accuracy in QCD perturbation theory using light-cone QCD sum rules. By processing these data along the lines proposed by Schmedding and Yakovlev, and recently revised by us, we obtain new constraints for the Gegenbauer coefficients $a_{2}$ and $a_{4}$, as well as for the inverse moment $x^{-1}$ of the pion distribution amplitude (DA). The former determine the pion DA at low momentum scale, the latter is crucial in calculating pion form factors. From the results of our analysis we conclude that the data confirm the end-point suppressed shape of the pion DA we previously obtained with QCD sum rules and nonlocal condensates, while the exclusion of both the asymptotic and the Chernyak--Zhitnitsky DAs is reinforced at the $3σ$- and $4σ$-level, respectively. The reliability of the main results of our updated CLEO data analysis is demonstrated. Our pion DA is checked against the di-jets data from the E791 experiment, providing credible evidence for our results far more broadly.

hep-ph↗

arXiv2000

Parton Skewed Distributions in the Pion and Quark-Hadron Duality

Applying arguments based on the operator product expansion for a three-point correlator and relying on quark-hadron duality, we derive an expression for the skewed (non-forward) parton distribution in the pion in the case of a zero-skewedness parameter, {\cal F}^{ψ|π}_{ζ=0}(X;t). We expect that our result is relevant for moderately large momentum transfers 1 < t < 10 GeV^2. In addition, we construct a purely phenomenological factorized model for the same quantity in close analogy to Radyushkin's model, originally proposed for skewed distributions of quarks in the nucleon. Though the quark-hadron duality approach supports theoretically the factorized model, the two models exhibit a different behavior in the parton momentum fraction X at any fixed t. The relevant process to distinguish between the two options seems to be the WACS off the pion that measures (to leading t/s-order) the inverse moment of the skewed distribution. Even after the inclusion of the first order kinematic t/s-corrections, the predictions for the cross section \frac{d σ}{d t}(s,t) at c.m.s. scattering angles \vartheta=30^{\circ} and 90^{\circ} differ by factors 3.5--3.9 and 2.9--7.5, respectively, so that a discrimination appears possible.

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