  Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the
energy frontier for photon-mediated interactions. UPC photons can be used for
many purposes, including probing low-$x$ gluons via photoproduction of dijets
and vector mesons, probes of beyond-standard-model processes, such as those
enabled by light-by-light scattering, and studies of two-photon production of
the Higgs.
