Anomalous ionization loss of high-energy e+e− pairs in thin targets

The problem of ionization loss of a high-energy electron-positron pair in a system of two plates - thick upstream, in which the pair is created, and thin downstream - is considered. It is shown that the process of transition radiation formation after the pair emission from the upstream plate significantly influences upon its ionization loss in the downstream plate. The consideration is made without the use of approximation of parallel electron and positron velocities which is widely applied for calculation of pair ionization loss. It is demonstrated that such approach reveals new peculiar features of asymptotical behavior of ionization loss in this process at large distance between the plates.