Aspects of supercritical heavy ion collisions

In collisions of very heavy ions 'supercritically' strong electric fields can be created transiently. In the presence of a supercritical field the neutral vacuum state of QED becomes unstable and decays into a charged vacuum, signalled by the spontaneous emission of positrons. Consequently the emission of positrons is strongly enhanced in high-Z collisions. Clear experimental signals for spontaneous positron creation are still missing and could only be expected from collisions with a prolonged time scale. We discuss possible scenarios for this to happen and indirect methods to perform a spectroscopy of superheavy quasimolecules