Autoionizing states and their relevance in electron-ion recombination

Atomic physics plays an important role in determining the evolution stages in a wide range of laboratory and cosmic plasmas. Therefore, the main contribution to our ability to model, infer and control plasma sources is the knowledge of underlying atomic processes. Of particular importance are reliable low temperature dielectronic recombination (DR) rate coefficients. This thesis provides systematically calculated DR rate coefficients of lithium-like beryllium and sodium ions via ∆n = 0 doubly excited resonant states. The calculations are based on complex-scaled relativistic many-body perturbation theory in an all-order formulation within the single- and double-excitation coupled-cluster scheme, including radiative corrections. Comparison of DR resonance parameters (energy levels, autoionization widths, radiative transition probabilities and strengths) between our theoretical predictions and the heavy-ion storage rings experiments (CRYRING-Stockholm and TSRHeidelberg) shows good agreement. The intruder state problem is a principal obstacle for general application of the coupled-cluster formalism on doubly excited states. Thus, we have developed a technique designed to avoid the intruder state problem. It is based on a convenient partitioning of the Hilbert space and reformulation of the conventional set of pairequations. The general aspects of this development are discussed, and the effectiveness of its numerical implementation (within the non-relativistic framework) is selectively illustrated on autoionizing doubly excited states of helium.

Studies of Heavy Baryons in DELPHI and Radiation Monitoring in DØ

Between the years 1992 and 1995 about 3.5 million hadronic Z decays were collected by the DELPHI detector at CERN. This data has been used to measure the production and lifetime of the beauty strange baryon Ξb, in the inclusive decay channel Ξb →Ξ-ℓ- X. The Ξ- baryon was reconstructed through the decay Ξ- → Λ π-, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Ξb selection. A search for the Ξb baryon was also performed using an alternative method of reconstructing the Ξ- baryon. A measurement of the production of the charmed strange baryon Ξc in the decay channel Ξc → Ξ-π+ using the same data is also presented. The radiation monitoring system of the Silicon Microstrip Tracker in the DØ detector is studied and used to estimate the radiation dose received by the Silicon detector during normal running conditions of the TeVatron accelerator.