Illuminating Nuclear Structure with Photons in Ultraperipheral Heavy-Ion Collisions

All nuclear matter consists of tiny particles called quarks and gluons. In particular, gluons become increasingly dominant constituents of nuclear matter when being probed at higher energies or smaller Bjorken-x values. This has led to the intriguing question of the ultimate fate of nuclear gluonic structures at extreme density. Photons have been used to probe the nuclear structure for many decades. Ultraperipheral collisions (UPCs) are collisions of relativistic heavy ions at impact parameters larger than the sum of their nuclear radius. The intense electromagnetic fields generated by the relativistic heavy ions can be treated as a flux of linearly polarized quasi-real photons. In UPCs, the coherent heavy-flavor vector meson production via photon-nuclear interactions, fueled by the intense photon flux between the ions, is particularly interesting, since its cross-section is directly sensitive to the nuclear gluon density. In this talk, we will review the recent progress in understanding the gluonic structure of the nucleus through UPC photoproduction and discuss the relevant physics implications, and future opportunities.