APEX: An experiment to study correlated positron-electron production in heavy ion collisions

he production of positrons in heavy ion collisions has been of great interest during the past decade. The unexpected discovery of correlated sharp positron-electron peaks in the energy distributions has motivated further research. In two independent experiments, several peaks have been studied, but their origin still remains unclear. The limitations of these first studies prompted a new experiment (APEX) to be designed. It has been assembled at Argonne National Laboratory, where beams of very heavy ions at Coulomb barrier energies are available from the ATLAS accelerator.;This dissertation reports on the design and instrumentation of the APEX spectrometer, and illustrates its performance with the first data. A solenoid magnetic field is used for transporting leptons away from the target and focusing them on arrays of Si detectors. The 511 keV...