Metastable States of Si^- Observed in a Cryogenic Storage Ring

This thesis deals with the analysis of data from the Si^- measurements performed in 2015 at the Cryogenic Storage Ring (CSR) located at the Max Planck Institute for Nuclear Physics. The Si^- ion has four metastable fine-structure levels which decay to the ground state with certain radiative lifetimes. So far, none of these lifetimes have been determined experimentally. In the CSR experiments, the ion beam was sampled by two lasers at regular intervals and the photodetachment products were detected. To understand the physical processes behind the observed count rates, a model is constructed. The model equations are then solved to demonstrate that the count rates can be described by a sum of several exponential decay functions corresponding to the different radiative decays. For the analysis, a fit function is first applied to the measured data in order to derive values for the radiative lifetimes. The model itself is then used to try and verify the radiative lifetimes available from two theoretical calculations. It is found that at least one metastable state is very long-lived and at least two have short, but distinct, lifetimes. This contradicts one set of theoretical lifetimes; the results regarding the other ones remain inconclusive