First observation of the deflection of a 33 TeV Pb ion beam in a bent silicon crystal

For the first time, the deflection of an ultra-relativistic, fully stripped Pb⁸²⁺ ion beam in a bent silicon crystal has been observed. The ions were provided by the CERN-SPS in the H4 beam at a momentum of 400 GeV/c per unit of charge. A 60 mm long silicon crystal, bent over 50 mm to give a 4 mrad deflection angle, was used in this experiment. The measured Pb ion deflection efficiency is comparable to the one obtained with protons at an equivalent ratio of momentum per charge, and is found to be about 15% for a beam with a divergence of 35 microradians (FWHM). The interaction rate observed in a background counter is found to drop when the crystal is well aligned with the beam. This corroborates further the channeling model, which predicts that channeled ions are steered away from regions of high electron densities as well as the nuclei in the crystal