Diffusion of High-Energy Negatively Charged Particles in the Field Atomic Strings of an Oriented Crystal

The work analyzes the dependence of the diffusion index of high-energy negatively charged particles on the energy of the transverse motion in oriented crystal. The crystal had an axial orientation relative to the direction of particle incidence. The analysis was carried out using the example of π− mesons with a momentum of 100 GeV/c that impinged on a silicon crystal, which corresponds to the conditions achievable on secondary beam of the the CERN SPS accelerator. The analysis showed that the dependence under consideration is not monotonic. It has a minimum in the energy region slightly exceeding the value of the potential energy of particles at the saddle point of the potential of crystal atomic strings. At higher values of the energy of transverse motion of particles E⊥, the diffusion index increases with increasing E⊥, since this increases the average absolute value of the velocity of particle motion in the plane orthogonal to the crystal axis, near which motion takes plase. The increase in the diffusion index at low values of E⊥ is associated with the manifestation of incoherent scattering of particles on thermal vibrations of crystal atoms. The analysis carried out in the work is of interest both for a deeper understanding of the process of high-energy negatively charged particle beams passage through oriented crystals, and for improving methods for charged particle beams steering with a help of straight and bent oriented crystals.