Ultra-Peripheral Collisions with STAR at RHIC

Abstract

The strong electromagnetic fields of heavy nuclei can produce a wide variety of two-photon and photonuclear reactions at relativistic ion colliders. We present recent results from the STAR collaboration on these `ultra-peripheral' interactions, focusing on vector meson production and interferometry, and on $e^+e^-$ pair production. The vector meson interferometry occurs because of the symmetric initial state: nucleus 1 can emit a photon which scatters from nucleus 2, emerging as a vector meson, or vice-versa. The two processes are indistinguishable, and so interfere, even though the production points are separated enough that the produced mesons decay before their wave functions can overlap, so the system can be used for interesting tests of quantum mechanics.