Observation of Positron Creation in Superheavy Ion-Atom Collision Systems

Abstract

We report the first observation of positron creation in high-energy $^{208}\mathrm{Pb}$ + $^{208}\mathrm{Pb}$ collisions and establish that a dominant fraction of the positron yield is from nonnuclear origins. The excess positron intensity observed over nuclear emission and its projectile energy dependence is consistent with recent predictions for pair-creation processes in the strong time-varying electric fields produced by the combined nuclear charges of the quasimolecular system formed in the collision.