Ultra-peripheral heavy-ion collisions (UPC) provide unique opportunities to
study processes under strong electromagnetic fields. Highly-charged moving ions
carry strong electromagnetic fields that act as fields of photons. The exchange
of photons could induce photonuclear and two-photon interactions as well as
excite the ions into giant dipole resonances (GDRs) or even higher excitation.
The GDRs typically decay by emitting photons and even a single neutron, while
high-excited resonances usually decay by emitting two or more photons and/or
neutrons. On the other hand, the electromagnetic fields of heavy ions are very
strong, so one of the two colliding ions is enforced by the other's
electromagnetic field. As a result, the two colliding ions are pushed into
opposite directions by the electromagnetic forces, and thus the neutrons
emitted from different ions could present a back-to-back correlation. Using a
Monte-Carlo simulation implementing the electromagnetic fields as well as the
neutron emission from previous measurements or model calculations, we
qualitatively demonstrate that the above electromagnetic effect is large enough
to be observed in UPC, which would provide a clear means to study the strong
electromagnetic fields and its effects.Comment: 4 pages, 3 figure