Observation of proton reflection on bent silicon crystals at the CERN SPS

Abstract

We report the observation of the so-called volume reflection effect with 400 GeV/c protons interacting with bent silicon crystals in the H8 beam line performed by the H8RDD22 Collaboration at the CERN SPS. The volume reflection is an effect of the same nature of the particle channeling among the crystalline planes of a bent crystal. The reflection occurs at the tangency point of a particle trajectory with the bent crystalline planes where the transverse component of the particle momentum is reversed. The measurements were realized with a high spatial resolution detector mainly based on silicon microstrips showing the effect on particle trajectories of bent silicon crystals in several configurations. The proton beam was deviated in a direction opposite to that of channeling by 12-14 murad, which is 1.3 times the critical angle, with an efficiency greater than 97% in a range of the proton-to-crystal incident angle as wide as the bending angle of crystallographic planes. This evidence opens new perspectives for manipulation of high-energy beams, e.g., for collimation and extraction in the new-generation of hadron colliders or as a method for high-energy experiments in the region close to the circulating beam.