B. G. Shaikhatdenov

Analytic and “frozen” coupling constants in QCD up to NNLO from DIS data

Deep inelastic scattering data on the F2 structure function provided by the BCDMS, SLAC, and NMC Collaborations are analyzed in the nonsinglet approximation with the analytic and “frozen” modifications of the strong-coupling constant featuring no unphysical singularity (the Landau pole). Improvement of agreement between theory and experiment, with respect to the case of the standard perturbative definition of αs considered recently, is observed and the higher-twist terms are shown to reduce at the next-to-next-to-leading order accuracy thus confirming earlier studies.

Q2 evolution of parton distributions at small values of x: Effective scale for combined H1 and ZEUS data on the structure function F2

An expression for the structure function F2 in the form of Bessel functions at small values of the Bjorken variable x is used. This expression was derived for a flat initial condition in the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations. The argument of the strong coupling constant was chosen in such a way as to annihilate the singular part of the anomalous dimensions in the next-to-leading-order of perturbation theory. This choice, together with the frozen and analytic versions of the strong coupling constant, is used to analyze combined data of the H1 and ZEUS Collaborations obtained recently for the structure function F2.

Strong coupling constant from QCD analysis of the fixed-target DIS data

Deep inelastic scattering data on F2 structure function obtained in fixed-target experiments were analyzed in the valence quark approximation with a next-to-next-to-leading-order accuracy. The strong coupling constant is found to be αs (MZ2) = 0.1157 ± 0.0022 (total experimental error), which is seen to be well compatible with the average world value. This study is meant to at least partially explain differences in the predictions for observables at the LHC found recently, caused by usage of various sets of parton distribution functions obtained by different groups.

QED correction to the radiative tail from the elastic peak in deep inelastic scattering

We calculate DIS cross section under kinematical requirements when a final hadron state is a single proton. The process in the lowest order is known as radiative tail from elastic peak. We take into account correction, coming from emission of virtual and soft real photons, to the amplitude of this process as well as the one, induced by emission of additional hard photon and a hard pair. Resulting contributions of these channels are presented in the leading and, partly, next-to-leading logarithmic approximations. Some general expressions for the photon contributions are given. Numerical results are presented for kinematical conditions of the current experiments on DIS.

Gottfried Sum Rule in QCD Nonsinglet Analysis of DIS Fixed-Target Data

Deep-inelastic-scattering data from fixed-target experiments on the structure function F2 were analyzed in the valence-quark approximation at the next-to-next-to-leading-order accuracy level in the strong-coupling constant. In this analysis, parton distributions were parametrized by employing information from the Gottfried sum rule. The strong-coupling constant was found to be αs(M2Z) = 0.1180 ± 0.0020 (total expt. error), which is in perfect agreement with the world-averaged value from an updated Particle Data Group (PDG) report, αPDGs (M2Z) = 0.1181 ± 0.0011. Also, the value of 〈x〉u−d = 0.187 ± 0.021 found for the second moment of the difference in the u- and d-quark distributions complies very well with the most recent lattice result 〈x〉LATTICEu−d = 0.208 ± 0.024.

Single-spin asymmetry in deeply virtual Compton scattering: Fragmentation region of polarized lepton

For the kinematical region when a hard photon is emitted predominantly close to the direction of motion of a longitudinally polarized initial electron and relatively small momentum transfer to a proton we calculate the azimuthal asymmetry of photon emission. It arises from the interference of the Bethe-Heitler amplitude and those which are described by a heavy photon impact factor. Azimuthal asymmetry does not decrease in the limit of infinite cms energy. Lowest order expression for the impact factor of a heavy photon is presented.