arXiv subjects
Publications and source records attributed to E. A. Kuraev.
QED processes at electron-positron colliders are considerd. We present differential cross-sections for large-angle Bhabha scattering, annihilation into muons and photons. Radiative corrections in the first order are taken into account exactly. Leading logarithmic contributions are calculated in all orders by means of the structure-function method. An accuracy of the calculation can be estimated about 0.2%.
Processes of electron-positron annihilation into charged pions and kaons are considered. Radiative corrections are taken into account exactly in the first order and within the leading logarithmic approximation in higher orders. A combined approach for accounting exact calculations and electron structure functions is used. An accuracy of the calculation can be estimated about 0.2%.
The lowest order QED radiative corrections to the cross-section of the recharged process of transition of two charged pions to two neutral ones and to the pionium life time are calculated in frames of scalar QED. It is argued that the ultraviolet cut--off of the loop momentum is to be chosen of order of $ρ$ meson mass. This fact permits to perform the calculation in frames of Effective Chiral Lagrangian theory with vector-meson dominance. The Coulomb factor corresponding to interaction in the initial state, shown, is to be removed to avoid the double counting. Resulting value of the radiative correction to the pionium life time is -0.25%.
Analytical formulae for small-angle Bhabha scattering cross-section at LEP1 are given for the case of wide-narrow angular acceptance. Inclusive and calorimeter event selections are considered. Numerical results are presented.
The result of lowest-order perturbation theory calculations of the photon and positron spectra in radiative pion(e2) decay are generalized to all orders of perturbation theory using the structure-function method. An additional source of radiative corrections to the ratio of the positron and muon channels of pion decay, due to emission of virtual and real photons and pairs, is considered. It depends on details of the detection of the final particles and is large enough to be taken into account in theoretical estimates with a level of accuracy of 0.1%.
We construct the evolution equations for the twist-3 chiral-odd spin independent fracture functions in QCD. The Gribov-Lipatov reciprocity relation is fulfilled at the one-loop level for the quasi-partonic two-particle cut vertices only. It is found that the rang of the anomalous dimensions matrix is infinite for any given moment of the three-parton fracture function as distinguished from the case of DIS-distributions where the rang of the matrix was finite and increases with the number of the moment. In the multicolour limit $N_c \to \infty$ the evolution equation for the quark-gluon-quark correlation function decouples from another equation in the system and becomes homogeneous provided we discard the quark mass effects. This fact provides an opportunity to find its analytic solution explicitly in nonlocal form similarly to the DIS.
A closed expression for the differential cross section of the large-angle Bhabha $e^+ e^-$ scattering which explicitly takes into account the leading and next-to-leading contributions due to the emission of two hard photons is presented. Both collinear and semi-collinear kinematical regions are considered. The results are illustrated by numerical calculations.
We present the calculation of the elastic and inelastic high--energy small--angle electron--positron scattering with a {\it per mille} accuracy. PACS numbers 12.15.Lk, 12.20.--m, 12.20.Ds, 13.40.--f
We consider small--angle electron--positron scattering in Quantum Electrodynamics. Leading logarithmic contributions to the cross--section are explicitly calculated to three loop. Next--to--leading terms are exactly computed to two loop. All the radiative corrections due to photons as well as pair production are taken into account. The impact of newly evaluated next-to-leading and higher order leading corrections is discussed and numerical results are explicitly given. The results obtained are generally valid for high and low energy $e^+e^-$ colliders. At LEP and SLC these results can be used to reduce the uncertainty on the cross--section below the per mille level. PACS numbers 12.15.Lk, 12.20.--m, 12.20.Ds, 13.40.--f
The elastic and inelastic high--energy small--angle electron--positron scattering is considered. All radiative corrections to the cross--section with the relative accuracy $δσ/ σ= 0.1 \% $ are explicitly taken into account. According to the generalized eikonal representation for the elastic amplitude, in higher orders only diagrams with one exchanged photon may be considered. Single photon emission with radiative corrections and next--to--leading two--photon and pair production diagrams are evaluated, together with leading three--loop corrections. All contributions have been calculated analytically. We integrate the calculated distributions over typical for LEP~1 experiments intervals of angles and energies. To the leading approximation, the results are shown to be described in terms of kernels of electron structure functions. Some numerical results are presented. PACS numbers 12.15.Lk, 12.20.--m, 12.20.Ds, 13.40.--f
Radiative corrections due to the production of virtual as well as real soft and hard pairs in small-angle Bhabha scattering are calculated analytically. Both the collinear and the semi-collinear kinematical regions of hard pair production are considered. The calculation, within the leading and next-to-leading logarithmic approximation, provides an accuracy of O(0.1%). Numerical results show that the effects of pair production have to be taken into account for a luminosity determination accurate to O(0.1%) at LEP.
The dominant contribution to the $π^0 \to 4γ$ branching ratio, coming from purely electromagnetic photon-splitting graph, is calculated. The result $Br(π^0 \to 4γ) \simeq (2.6 \pm 0.1) \cdot 10^{-11}$ is about three orders of magnitude below the present experimental limit.
The manifestations of the $ω\to 3π$ contact term and its unitary partners are investigated in the framework of the chiral effective lagrangian theory with vector mesons. We conclude that nowadays the existence and magnitude of the contact term can be extracted neither from theory, nor experiment. The theoretical uncertainty is caused by the one-loop corrections. Some speculations about them lead to the generalized KSRF relation $\frac{f_π^2g^2_{ρππ}}{m_ρ^2}=\frac{m_K}{2\sqrt{2} πf_π}$.
The decay modes $ρ^0 \to 2π^+ 2π^-$ and $ρ^0 \to 2π^0 π^+ π^-$ are considered in the framework of the low energy effective chiral Lagrangian. The obtained values of the decay widths $Γ(ρ^0\to 2 π^+ 2 π^-)=$ $(16 \pm 1){\rm keV}$ and $Γ(ρ^0\to 2 π^0 π^+ π^-)= (6.0 \pm 0.2)$keV do not contradict the existing upper limits and seem to be big enough for the corresponding processes to be observed in future high luminosity experiments.
We discuss special type of polarization asymmetry (``handedness") in the process $e^+e^-\to 4π$, when one of initial particles is longitudinally polarized. The asymmetry is proportional to the degree of polarization and to the width to mass ratio of rho-meson. It can reach 4-5\% in some kinematical region. Both channels $2 π^+ 2 π^-$ and $2 π^0 π^+ π^-$ are considered in the framework of the effective chiral lagrangian with vector mesons, in the energy range $\sim 1$ GeV. The corresponding total cross sections are also calculated.