edoc: No conditions. Results ordered -Date Deposited. 2024-10-08T15:45:57ZEPrintshttps://edoc.unibas.ch/images/uni-logo.jpghttps://edoc.unibas.ch/2012-09-14T06:45:42Z2017-09-20T12:41:23Zhttps://edoc.unibas.ch/id/eprint/19656This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/196562012-09-14T06:45:42ZCoulomb distortion of relativistic electrons in the nuclear electrostatic fieldContinuum states of the Dirac equation are calculated numerically for the electrostatic field generated by the charge distribution of an atomic nucleus. The behavior of the wave functions of an incoming electron with given asymptotic momentum in the nuclear region is discussed in detail and the results are compared to different approximations used in the data analysis for quasielastic electron scattering off medium and highly charged nuclei. It is found that most of the approximations provide an accurate description of the electron wave functions in the range of electron energies above 100 MeV typically used in experiments for quasielastic electron scattering off nuclei only near the center of the nucleus. It is therefore necessary that the properties of exact wave functions are investigated in detail in order to obtain reliable results in the data analysis of quasielastic (e, e'p) knockout reactions or inclusive quasielastic (e, e') scattering. Detailed arguments are given that the effective momentum approximation with a fitted potential parameter is a viable method for a simplified treatment of Coulomb corrections for certain kinematical regions used in experiments. Numerical calculations performed within the framework of the single-particle shell model for nucleons lead to the conclusion that our results are incompatible with calculations performed about a decade ago, where exact electron wave functions were used in order to calculate Coulomb corrections in distorted-wave Born approximation. A discussion of the exact solutions of the Dirac equation for free electrons in a Coulomb field generated by a point-like charge and some details relevant for the numerical calculations are given in the appendix. Andreas AsteCyrill von ArxDirk Trautmann2012-09-14T06:45:41Z2017-02-09T09:47:38Zhttps://edoc.unibas.ch/id/eprint/19655This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/196552012-09-14T06:45:41ZMulti-photon exchange processes in ultraperipheral relativistic heavy-ion collisionsThe very strong electromagnetic fields present in ultraperipheral relativistic heavy-ion collisions lead to important higher-order effects of the electromagnetic interaction. These multi-photon exchange processes are studied using perturbation theory and the sudden or Glauber approximation. In many important cases, the multi-photon amplitudes factorize into independent single-photon amplitudes. These amplitudes have a common impact parameter vector, which induces correlations between the amplitudes. Impact-parameter dependent equivalent-photon spectra for simultaneous excitation are calculated, as well as, impact-parameter dependent γγ-luminosities. Excitations, like the multi-phonon giant dipole resonances, vector meson production and multiple e+e−-pair production can be treated analytically in a bosonic model, analogous to the emission of soft photons in QED. Gerhard BaurKai HenckenAndreas AsteDirk TrautmannSpencer Klein2012-09-14T06:44:49Z2017-02-09T07:22:31Zhttps://edoc.unibas.ch/id/eprint/19578This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/195782012-09-14T06:44:49ZElectron positron pair production in the external electromagnetic field of colliding relativistic heavy ionsThe results concerning the production in peripheral highly relativistic heavy-ion collisions presented in a recent paper by Baltz et al. are rederived in a very straightforward manner. It is shown that the solution of the Dirac equation directly leads to the multiplicity, i.e. to the total number of electron–positron pairs produced by the electromagnetic field of the ions, whereas the calculation of the single pair production probability is much more involved. A critical observation concerns the unsolved problem of seemingly absent Coulomb corrections (Bethe–Maximon corrections) in pair production cross sections. It is shown that neither the inclusion of the vacuum–vacuum amplitude nor the correct interpretation of the solution of the Dirac equation concerning the pair multiplicity is able the explain (from a fundamental point of view) the absence of Coulomb corrections. Therefore the contradiction has to be accounted to the treatment of the high energy limit. Andreas AsteGerhard BaurKai HenckenDirk TrautmannGünter Scharf2012-03-22T13:49:06Z2017-02-09T07:10:57Zhttps://edoc.unibas.ch/id/eprint/9325This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/93252012-03-22T13:49:06ZElectromagnetic pair production with captureCalculations of the electron-positron pair production by a single photon in the Coulomb field of a nucleus with simultaneous capture of the electron into the K shell are presented. Numerical results are given for some nuclear charges up to 92 and energies from threshold to 15 MeV. Using the equivalent-photon method of Weizsäcker and Williams, reliable estimates of the cross sections for the production of e+e- (K orbit) pairs by very-high-energy fully stripped heavy ions can be made for arbitrary nuclear charges. Andreas AsteKai HenckenDirk TrautmannGerhard Baur