High-efficiency deflection of high-energy negative particles through axial channeling in a bent crystal

Deflection due to axial channeling in a silicon crystal bent along the < 111 > axis was observed for 150 GeV/c negative particles, mainly pi(-) mesons, at one of the secondary beams of the CERN SPS. The whole beam was deflected to one side with the efficiency of about 90% and with the peak position at the bend crystal angle alpha = 43 mu rad. The deflection occurs mainly due to doughnut scattering of above-barrier particles by the atomic strings of the crystal. However, due to a high probability of particle recapture into bound states with the atomic strings their contribution to the deflection should be about 15% for Our case according to simulation results.