Coherent Coulomb Excitation of Relativistic Nuclei in Aligned Crystal Targets

We study coherent Coulomb excitation of ultrarelativistic nuclei passing through an aligned crystal target. We develop multiple-scattering description of this process, which consistently incorporates both the specific resonant properties of particle-crystal interactions and the shadowing effect typical of the diffractive scattering. We emphasize that the effect of quantum mechanical diffraction makes the physics of ultrarelativistic nuclear excitations cardinally different from the physics of nonrelativistic atomic excitations experimentally studied so far. It is found that, at small transverse momenta q_⊥, the shadowing effect drastically changes the dependence of coherent amplitudes on crystal thickness L from the widely discussed growth ∝L, typical of the Born approximation, to the inverse-thickness attenuation law. At relatively large q_⊥, no attenuation effect is found, but the coherency condition is shown to pose stringent constraint on the increase in the transition rate with growing L.