Double lepton pair production with electron capture in relativistic heavy--ion collisions

We present a theoretical study of a double lepton pair production in ultra--relativistic collision between two bare ions. Special emphasis is placed to processes in which creation of (at least one) $e^+ e^-$ pair is accompanied by the capture of an electron into a bound ionic state. To evaluate the probability and cross section of these processes we employ two approaches based on (i) the first--order perturbation theory and multipole expansion of Dirac wavefunctions, and (ii) the equivalent photon approximation. With the help of such approaches, detailed calculations are made for the creation of two bound--free $e^+ e^-$ pairs as well as of bound--free $e^+ e^-$ and free--free $\mu^+ \mu^-$ pairs in collisions of bare lead ions Pb$^{82+}$. The results of the calculations indicate that observation of the double lepton processes may become feasible at the LHC facility.Comment: 12 pages, 1 figur

Negative-continuum dielectronic recombination into excited states of highly-charged ions

The recombination of a free electron into a bound state of bare, heavy nucleus under simultaneous production of bound-electron--free-positron pair is studied within the framework of relativistic first--order perturbation theory. This process, denoted as "negative-continuum dielectronic recombination" leads to a formation of not only the ground but also the singly- and doubly-excited states of the residual helium-like ion. The contributions from such an excited--state capture to the total as well as angle-differential cross-sections are studied in detail. Calculations are performed for the recombination of (initially) bare uranium U$^{92+}$ ions and for a wide range of collision energies. From these calculations, we find almost 75 % enhancement of the total recombination probability if the excited ionic states are taken into account.Comment: 8 pages, 4 figures, accepted to PR

Target effects in negative-continuum assisted dielectronic recombination

The process of recombination of a quasi-free electron into a bound state of an initially bare nucleus with the simultaneous creation of a bound-electron--free-positron pair is investigated. This process is called the negative-continuum assisted dielectronic recombination (NCDR). In a typical experimental setup, the initial electron is not free but bound in a light atomic target. In the present work, we study the effects of the atomic target on the single and double-differential cross sections of the positron production in the NCDR process. The calculations are performed within the relativistic framework based on QED theory, with accounting for the electron-electron interaction to first order in perturbation theory. We demonstrate how the momentum distribution of the target electrons removes the non-physical singularity of the differential cross section which occurs for the initially free and monochromatic electrons

Solution of two-center time-dependent Dirac equation in spherical coordinates: Application of the multipole expansion of the electron-nuclei interaction

A non-perturbative approach to the solution of the time-dependent, two-center Dirac equation is presented with a special emphasis on the proper treatment of the potential of the nuclei. In order to account for the full multipole expansion of this potential, we express eigenfunctions of the two-center Hamiltonian in terms of well-known solutions of the "monopole" problem that employs solely the spherically-symmetric part of the interaction. When combined with the coupled-channel method, such a wavefunction-expansion technique allows for an accurate description of the electron dynamics in the field of moving ions for a wide range of internuclear distances. To illustrate the applicability of the proposed approach, the probabilities of the K- as well as L- shell ionization of hydrogen-like ions in the course of nuclear alpha-decay and slow ion-ion collisions have been calculated

Inter-electronic interaction effects on the polarization of recombination photons

A theoretical investigation of the radiative capture of an electron into a bound state of heavy, hydrogen-like ion is presented. Special attention is paid to the question of how the linear polarization of the emitted radiation is affected by the inter-electronic interaction effects. An analysis of these effects is performed within both, the screening-potential approximation and the perturbation theory that treats rigorously the electron correlations to the first order in the parameter 1/Z. By making use of these two approaches, detailed calculations are performed for relativistic collisions of hydrogen-like europium Eu^{62+}, bismuth Bi^{82+} and uranium U^{91+} ions with free electron and low-Z atomic targets. Results of the calculations indicate that the two-electron effects may significantly influence the polarization properties of the recombination x-rays; the effect which can be observed by the present-day polarization detectors

QED calculation of the 2p3/2-2p1/2 transition energy in five-electron ion of argon

We perform ab initio QED calculation of the (1s)^2(2s)^22p_{3/2} - (1s)^2(2s)^22p_{1/2} transition energy in the five-electron ion of argon. The calculation is carried out by perturbation theory starting with an effective screening potential approximation. Four different types of the screening potentials are considered. The rigorous QED calculations of the two lowest-order QED and electron-correlation effects are combined with approximate evaluations of the third- and higher-order electron-correlation contributions. The theoretical value for the wavelength obtained amounts to 441.261(70) (nm, air) and perfectly agrees with the experimental one, 441.2559(1) (nm, air).Comment: 10 pages, 3 figures, 1 tabl

Quantum electrodynamics of heavy ions and atoms

The present status of quantum electrodynamics (QED) theory of heavy few-electron ions is reviewed. The theoretical results are compared with available experimental data. A special attention is focused on tests of QED at strong fields and on determination of the fundamental constants. A recent progress on calculations of the QED corrections to the parity nonconserving 6s-7s transition amplitude in neutral Cs is also discussed.Comment: Talk at ICAP 2006, Innsbruck, Austri

Young-type interference in projectile-electron loss in energetic ion-molecule collisions

Under certain conditions an electron bound in a fast projectile-ion, colliding with a molecule, interacts mainly with the nuclei and inner shell electrons of atoms forming the molecule. Due to their compact localization in space and distinct separation from each other these molecular centers play in such collisions a role similar to that of optical slits in light scattering leading to pronounced interference in the spectra of the electron emitted from the projectile.Comment: 4 pages, 3 figure