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Ultra-peripheral Collisions at RHIC: An Experimental Overview

Ultra-peripheral collisions (UPCs) of ions allow us to study photonuclear and two-photon interactions at energies above those available at fixed target accelerators. For heavy ions, the couplings are large enough so that multi-photon interactions are possible, and higher order corrections are expected to be significant. In this writeup, I present some recent UPC results from the Relativistic Heavy Ion Collider (RHIC), and discuss some future prospects. I also draw parallels between UPC data and that expected at an electron-ion collider (EIC), and show how UPCs are a useful lead-in to EIC physics. This writeup is based on a talk at "Initial State 2014," (IS2014), with a focus on the newest results. One important result is that comparison of the RHIC (and LHC) results on coherent $ρ^0$ photoproduction show evidence for nuclear suppression, compared to a calculating based on $γp$ cross-sections.