Laser-Assisted Positron-Impact Ionization of Hydrogen Atoms
S. Taj, B. Manaut, E. Hrour, M. El Idrissi
Université Sultan Moulay Slimane, Faculté Polydisciplinaire, Equipe de Recherche en Physique Théorique et Matériaux (ERPTM), P.O. Box 523, Béni Mellal, 23000, Morocco
Received: May 2, 2018; revised version February 22, 2019; in final form March 14, 2019
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The theory of triple differential cross-sections, developed previously within the framework of nonrelativistic Schrödinger formalism, is extended to the relativistic treatment by using the Dirac-Volkov formalism. At high energies, the colliding particles lose their Coulomb character and the channel of the symmetric coplanar geometry is opened. In the first Born approximation, we have studied theoretically the laser-assisted relativistic ionization of hydrogen atoms by positron impact in this geometry. Triple differential cross-sections are calculated by using two approaches: (i) RPWSG to describe relativistic plane wave in the symmetric geometry, (ii) DVPWSG (Dirac-Volkov plane wave in the symmetric geometry) in which we take full account of the relativistic dressing effects, has been proposed to study the influence of laser field on the colliding particles. To check the consistency of our model, we have used, for comparison, the nonrelativistic approach: nonrelativistic plane wave in the symmetric geometry. Numerical results for the variation of relativistic triple differential cross-sections and their dependences on laser field parameters (intensity, frequency) and incident positron energy are also presented. As for the laser modifications, by summing over a very large number of exchanged photons, the laser-assisted triple differential cross-sections usually tends to approach the laser-free triple differential cross-sections, obeying the famous Kroll-Watson sum rule for positron projectile. In the absence, of any experimental data at high energies for this particular ionization process, we are not in a position to compare the present results with the experimental findings.

topics: positron impact, ionization hydrogen atom, laser assisted, QED calculations, relativistic scattering theory