Study of e+?(hye pair creation by 20150-GeV photons incident on a germanium crystal in alignment conditions

Abstract
We report on absolute measurements of the orientation dependence of the e+-e pair production by 20150-GeV photons aligned or nearly aligned with the 〈110〉 axial direction of a thin Ge crystal. The observed effects are very large, and are well described by theoretical predictions based on the existence of strong macroscopic fields in aligned crystals.