Pair production by 5–150 GeV photons in the strong crystalline fields of germanium, tungsten and iridium

Abstract

Experimental results for pair production by 20–150 GeV photons in a Ge crystal cooled to 100 K are presented. The results include total and differential enhancements for incidence of the photons along the (1 1 0) plane with angles 0–4.5 mrad to the 〈1 1 0〉 axis. For the first time, a comparison can be made with theoretical results which for incidence along the plane predict pronounced structural changes of a resonance type in the pair production yield as a function of angle to the axis. These changes originate from the coherent interaction with the strong field of the atomic strings in the crystal. Furthermore, results for pair production by 5–55 GeV photons in W and Ir crystals at temperatures between 100 and 300 K are presented. These results are for total enhancements with photons incident along the strongest axes in these materials, i.e. the 〈1 1 1〉 axis in W and the 〈1 1 0〉 axis in Ir. A clear disagreement with theoretical curves calls for improved calculations.