Measurements and theories of the King–Perkins–Chudakov effect

We discuss the available experimental results, based on cosmic rays as well as laboratory measurements, for the King–Perkins–Chudakov (KPC) effect where pairs – when detected close to the creation vertex – suffer a reduced energy loss due to the internal screening of the charges constituting the pair. It is shown that the overall best description of data is obtained from the original theoretical expression by Chudakov based on classical electrodynamics, or the semi-classical extension by Burkhardt. The expression used in some textbooks, based on the theory of Berestetskii and Geshkenbain, provides a somewhat poorer description of data, but – contrary to those of Chudakov and Burkhardt – is applicable in the limit of large distances to the creation vertex.