9 research outputs found
Direct calculation of the probability of pionium ionization in the target
We performed the first direct calculation of the probability of pionium
(pi+pi- atom) ionization in the target. The dependence of the probability of
pionium ionization in the target as a function of the pionium lifetime is
established. These calculations are of interest of the DIRAC experiment at
CERN, which aims to measure the pionium lifetime with high precision.Comment: 11 pages, 4 figures; submitted to "Physics of Atomic Nuclei"
("Yadernaya Fizika"
Contribution of -terms to the total interaction cross sections of relativistic elementary atoms with atoms of matter
It is shown that the corrections of order to the total cross
sections for interaction of elementary hydrogen-like atoms with target atoms,
reported in the previously published paper [S.Mrowczynski, Phys.Rev. D36, 1520
(1987)], do not include some terms of the same order of magnitude. That results
in a significant contribution of these corrections in particular cases. The
full -corrections have been derived and it is shown that they are
really small and could be omitted for most practical applications.Comment: 5 page
Coherent and incoherent atomic scattering: Formalism and application to pionium interacting with matter
The experimental determination of the lifetime of pionium provides a very
important test on chiral perturbation theory. This quantity is determined in
the DIRAC experiment at CERN. In the analysis of this experiment, the breakup
probabilities of of pionium in matter are needed to high accuracy as a
theoretical input. We study in detail the influence of the target electrons.
They contribute through screening and incoherent effects. We use Dirac-Hartree-
Fock-Slater wavefunctions in order to determine the corresponding form factors.
We find that the inner-shell electrons contribute less than the weakly bound
outer electrons. Furthermore, we establish a more rigorous estimate for the
magnitude of the contributions form the transverse current (magnetic terms thus
far neglected in the calculations).Comment: Journal of Physics B: Atomic, Molecular and Optical Physics;
(accepted; 22 pages, 6 figures, 26 references) Revised version: more detailed
description of DIRAC experiment; failure of simplest models for incoherent
scattering demonstrated by example
Density Matrix Kinetic Equation Describing a Passage of Fast Atomic Systems Through Matter
The quantum-mechanical consideration of a passage of fast dimesoatoms through
matter is given. A set of quantum-kinetic equations for the density matrix
elements describing their internal state evolution is derived. It is shown that
probabilistic description of internal dynamics of hydrogen-like atoms is
impossible even at sufficiently low energies because of the ``accidental''
degeneracy of their energy levels.Comment: 12 pages, LATEX, submitted to J. Phys.
First measurement of the atom lifetime
The goal of the DIRAC experiment at CERN (PS212) is to measure the
atom lifetime with 10% precision. Such a measurement would yield a
precision of 5% on the value of the -wave scattering lengths
combination . Based on part of the collected data we present a first
result on the lifetime, s, and
discuss the major systematic errors. This lifetime corresponds to
.Comment: 18 pages, 6 figure
Sca calculations of the proton induced alignment using relativistic hartree-fock wavefunctions
Proton-induced differentia] and total alignment is reviewed and some calculations presented. A density matrix formalism is employed as the theoretical framework and a more efficient expansion into state multipoles used. The collision T-matrix elements entering the expression for the alignment tensor are calculated in the semiclassical approximation to first order. A coordinate space formulation including classical hyperbolic trajectories for the projectile path is adopted here, to take proper account of deflection. Relativistic Hartree-Fock orbital wavefunctions for bound and continuum electronic states in the partial-wave expansion cover both screening and relativistic effects in the atom in a unifying scheme. The continuum orbitals are calculated iteratively until the frozen core VN-1 potential converges. © 1995 IOP Publication Ltd
SCA calculations of the inner shell ionization with Dirac-Fock electronic wave functions
The theory of inner shell ionization for arbitrary atomic shells is reviewed. Emphasis is on L- and M-shells in order to show how the proper screening formalism entering the electronic form factor affects the ionization probabilities. The radial wavefunctions in the form factor are computed as relativistic Hartree-Fock orbitals for both bound and continuum states. The continuum orbitals were evaluated in the V(N-1) potential with correct exchange. These results are then compared with the previous ones using screened hydrogen-like wavefunctions and also with the experimental data in some cases
Continuum wavefunction solver for GRASP
Relativistic VN-1 continuum orbitals are solved numerically within the framework of the GRASP code [K. Dyall et al., Comput. Phys. Commun. 55 (1989) 425]. Normalization is accomplished with a relativistic WKB method or curve fitting, depending on whether the core is an ion or is neutral. In the normalization, the phase shift (relative to hydrogen) is also calculated. The spacing of the radial grid at large distances is automatically determined to provide at least 10 grid points per half cycle of the wavefunction. Lagrange multipliers are automatically determined. © 1993