High-Energy Processes in Crystals: Radiation, Pair Creation, Photon Splitting and Pion Creation
In the three years since we suggested that an aligned crystal could significantly enhance the electron-positron pair-creation rate,1 considerable progress has been made in understanding the special role a crystal plays in quantum electrodynamics (QED) at GeV energies. Theoretical work by several groups have shown that both radiation and pair creation are most simply described by viewing the crystal as a source of large and effectively homogeneous electric fields.2,3,4,5 This “uniform-field approximation” gives qualitatively reasonable results when the crystal axis is in nearly perfect alignment with a beam of incident particles (electrons, positrons, or photons). The success of the uniform-field approximation is a consequence of the large mass enhancement of electrons and positrons with GeV energies. The motion of these leptons in the plane transverse to the aligned crystal axis can be accurately described by a nonrelativistic Schrödinger equation for a particle with a relativistically enhanced mass,6 and the large mass allows us to describe particle trajectories classically. The general agreement between theory and experimental data on high-energy radiation and “crystal-enhanced” pair creation is quite satisfactory. A review of the experimental results, and the appropriate references are given in the paper by A. Belkacem et al. in this volume.
KeywordsMomentum Transfer Incident Photon Crystal Axis Incident Photon Energy Pair Creation
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