Breakdown of Born-Oppenheimer Description Explains Neutron Compton Scattering Anomaly

摘要

Several neutron Compton scattering experiments reveal an apparent drop of the proton cross-section when the collision time Tq, is around 1 fs. Such small Tq corresponds to a large energy spread of the proton wave packet after collision, allowing it to access excited electronic levels. This non-adiabatic excitation of electrons leads to a distortion of the shape of the neutron scattering response function with some redistribution of intensity at energies higher than the nuclear recoil energy and a slight shift of the main neutron intensity peak to lower energies.