Special Aspects of the EPOS Experiments on Positron Emission from Superheavy Collision Systems

Abstract

The first observation of monoenergetic positrons emerging from collisions of very heavy nuclei (e.g. U+U, U+Cm etc) in experiments performed at GSI^1,2,), initiated substantial experimental and theoretical effort to understand the mechanisms that produce these positrons. Part of these conference proceedings reflects this endeavor to solve the “positron puzzle”. Two experimental results found by the EPOS collaboration³⁾ have been matter of extensive discussions in this context:

• a) the meaning of the projection windows on the kinematic heavy-ion correlation (“kinematic cuts”), which were set to achieve an optimal peak-to-background ratio of the positron lines above the spectrum of dynamical and nuclear positrons.

• b) The apparent “resonance-” or “threshold-” like dependence of the positron line production on the impact energy.