Opportunities of strong-field physics in middle-energy heavy-ion collisions

By colliding heavy ions at energies of O(1-10 GeV/nucleon), a super high-density state like that inside a neutron star may be created on Earth. Experiments are being planned worldwide to elucidate the properties of matter at such a high-density limit (e.g., FAIR, NICA, J-Parc-HI). In this talk, I would like to discuss the possibility that heavy-ion collisions at this energy scale (which I call "middle-energy" heavy-ion collisions) can be used not only to study the high-density limit but also provides a unique opportunity to study strong-field physics.

The basic idea is that the collided heavy ions form a gigantic ion with a large atomic number Z due to the Landau stopping picture valid at middle energies. A large Z produces a strong Coulomb electric field by compensating the smallness of the fine structure constant and thereby a strong field comparable to or larger than that of the critical electromagnetic field in QED may be created. If this idea is true, it is very interesting, since it is believed that it is impossible to create such an extremely strong field within the current experimental technology (e.g., intense laser).

In this talk, I present a quantitative estimation of electromagnetic field strength and spacetime volume in middle-energy heavy-ion collisions based on a hadron transport model (JAM) and show that a strong electromagnetic field above the critical field strength is indeed realized with a sufficiently large spacetime volume.